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We studied the effect of chemically active fluorine-containing additives AlF.sub.3, BaF.sub.2, and ZnF.sub.2 on the character of evaporation of some low-volatile elements from a refractory matrix in the crater of a DC arc electrode in the analysis of zirconium by atomic emission spectrometry. The additives cause the formation of volatile fluorides of low-volatile elements and their fractional evaporation with respect to the base element evaporation. Impurity fluorides rapidly and completely evaporate during the first 30 s of arcing, and only after that the intensive evaporation of the base begins. Such fractionation increases significantly the intensity of the spectral lines of impurities, decreases the background intensity, and, consequently, improves the limits of determination of low-volatile elements in zirconium oxide. Zinc fluoride is the most effective of the studied additives. Using zinc fluoride, we lowered the limits of determination of low-volatile elements by two orders of magnitude compared to the limits of determination in zirconium oxide without additives and improved the reproducibility of the results of determinations., Author(s): N. I. Zolotareva [sup.1] , S. S. Grazhulene [sup.1] Author Affiliations: (1) grid.425037.7, 0000 0004 0638 3022, Institute of Microelectronics Technology and High-Purity Materials, Russian Academy of Sciences, , [...]

The Margaree pluton extends for >40 km along the axis of the Ganderian Aspy terrane of northern Cape Breton Island, Nova Scotia. The pluton consists mainly of coarse-grained megacrystic syenogranite, intruded by small bodies of medium-grained equigranular syenogranite and microgranite porphyry, all locally displaying rapakivi texture. The three rock types have similar U-Pb (zircon) ages of 363 [+ or -] 1.6, 364.8 [+ or -] 1.6, and 365.5 [+ or -] 3.3 Ma, respectively, consistent with field and penological evidence that they are coeval and comagmatic. The rare earth elements display parallel trends characterized by enrichment in the light rare earth elements, flat heavy rare earth elements, moderate negative Eu anomalies, and, in some cases, positive Ce anomalies. The megacrystic and rapakivi textures are attributed to thermal perturbation in the magma chamber caused by the mixing of mafic and felsic magma, even though direct evidence of the mafic magma is mainly lacking at the current level of exposure. Magma evolution was controlled by fractionation of quartz, K-feldspar, and Na-rich plagioclase in molar proportions of 0.75:0.12:0.13. The chemical and isotopic (Sm-Nd) signature of the Margaree pluton is consistent with the melting of preexisting continental crust that was enriched in heat-producing elements, likely assisted by intrusion of mantle-derived mafic magma during Late Devonian regional extension. The proposed model involving magma mixing at shallow crustal levels in a cryptic silicic-mafic magma chamber during post-Acadian extension is consistent with models for other, better exposed occurrences of rapakivi granite in the northern Appalachian orogen. Key words: rapakivi, megacrysts, U-Pb zircon, Devonian, crystal fractionation, PER diagrams. Le pluton de Margaree s'etale sur plus de 40 km le long de l'axe du terrane ganderien d'Aspy du nord de l'île du Cap-Breton (Nouvelle-Ecosse). Le pluton est principalement constitue de syenogranite megacristique à grains grossiers, recoupe par de petits corps de syenogranite equigranulaire à grains moyens et de porphyre microgranitique, qui presentent tous une texture rapakivi. Les trois types de roche donnent des âges U-Pb sur zircons semblables de 363 [+ or -] 1,6, 364,8 [+ or -]1,6 et 365,5 [+ or -] 3,3 Ma, respectivement, ce qui concorde avec des observations petrologiques et de terrain indiquant qu'ils sont contemporains et comagmatiques. Les terres rares presentent des spectres paralleles caracterises par un enrichissement des terres rares legeres, des tronçons des terres rares lourdes plats, des anomalies negatives moderees d'Eu et, dans certains cas, des anomalies de Ce positives. Les textures megacristique et rapakivi sont attribuees à une perturbation thermique dans la chambre magmatique causee par le melange de magmas mafique et felsique, bien que des preuves directes de la presence d'un magma mafique soient generalement absentes au niveau d'exposition actuel. L'evolution du magma etait controlee par la cristallisation fractionnee du quartz, du feldspath potassique et du plagioclase riche en Na dans des proportions molaires de 0,75:0,12:0,13. Les signatures chimique et isotopique (Sm-Nd) du pluton de Margaree concordent avec la fusion de croûte continentale preexistante qui etait enrichie en elements thermogenes, vraisemblablement aidee par l'intrusion de magma mafique derive du manteau durant l'extension regionale au Devonien tardif. Le modele propose qui comprend le melange de magmas à des niveaux crustaux peu profonds dans une chambre magmatique siliceuse-mafique cryptique durant l'extension post-acadienne concorde avec les modeles proposes pour d'autres cas mieux exposes de granite rapakivi dans le nord de l'orogene des Appalaches. [Traduit par la Redaction] Mots-cles: rapakivi, megacristaux, U-Pb sur zircons, Devonien, cristallisation fractionnee, diagramme de Pearce., Introduction Rapakivi granite sensu stricto is characterized by the presence of plagioclase-mantled K-feldspar, independent of K-feldspar morphology or origin (Ramo and Haapala 1995). The debate over the formation of rapakivi [...]

The Machangqing Cu-Mo (Au) deposit is located in the central part of the Jinshajiang - Red River belt in the Sanjiang orogen, which lies across the Qiangtang terrane and western Yangtze craton, southwestern China. Zircon U-Pb dating constrains that the granite porphyry and porphyritic granite emplacements occurred at 35.92 [+ or -] 0.31 Ma and 34.92 [+ or -] 0.31 Ma, respectively. The Re-Os model ages of molybdenite are 34.94 [+ or -] 0.38 Ma. The new ages presented here, along with previously published data in the region, define a short duration of potassic magmatism and mineralization from 37 Ma to 34 Ma in the Jinshajiang - Red River belt. Zircon [Ce.sup.4+]/[Ce.sup.3+] values of the porphyritic granite and granite porphyry vary from 50.32 to 1579.20 (averaging 481.01) and 33.18 to 1511.80 (averaging 452.98), respectively, and the log(f[o.sub.2]) values vary from -6.66 to -23.86 and -9.88 to -25.18, respectively, which plot within the range of the fayalite-magnetite-quartz buffer curve to the magnetite-hematite buffer curve, indicating an oxidized magma source, which may have facilitated the Cu-Au enrichment. Zircons from granitoids show [epsilon]Hf(t) values ranging from -0.75 to +2.33 and crustal model ages between 0.9 and 1.1 Ga. The features of Lu-Hf isotopes and wide range of Mg#, Cr, and Ni contents imply that the magmas of the Machangqing granitoids were probably derived from partial melting of juvenile lower crust and mixed with some mantle melts. Combined with the features of the Machangqing granitoids, the following evolution process are concluded. During the Cenozoic, the India-Asia continental collision triggered upwelling of hot asthenosphere and underplating of the thickened juvenile lower crust, which caused the formation of mafic and felsic magmas. Those magmas ascended, mixed, crystallized, and formed Machangqing ore-bearing granitoids in an intracontinental extension setting. Key words: LA-ICP-MS zircon U-Pb dating, molybdenite Re-Os dating, oxidation magma, Machangqing Cu-Mo (Au) deposit, Jinshajiang - Red River belt, eastern Tibetan plateau. Le gisement de Cu-Mo (Au) de Machangqing est situe dans la partie centrale de la ceinture de failles de Jinshajiang - riviere Rouge de l'orogene de Sanjiang, qui enjambe le terrane de Qiangtang et le craton du Yangtze (sud-ouest de la Chine). La mineralisation à Cu-Mo (Au) est genetiquement associee à des stocks de granitoïdes comprenant un granite porphyrique et un porphyre granitique. La datation U-Pb sur zircons par LA-ICP-MS permet d'etablir que le porphyre granitique et le granite porphyrique ont ete mis en place à 35,92 [+ or -] 0,31 Ma et 34,92 [+ or -] 0,31 Ma, respectivement. L'âge modele Re-Os sur la molybdenite est de 34,94 [+ or -] 0,38 Ma, ce qui indiquerait un episode de magmatisme et de mineralisation paleogene à Machangqing. Les nouveaux âges presentes ici, combines à des âges dejà publies pour la region definissent un court intervalle de magmatisme potassique et de mineralisation de 37 Ma à 34 Ma dans la ceinture de Jinshajiang - riviere Rouge. Les valeurs de [Ce.sup.4+]/[Ce.sup.3+] des zircons du granite porphyrique et du porphyre granitique vont de 50,32 à 1579,20 (moyenne de 481,01) et de 33,18 à 1511,80 (moyenne de 452,98), respectivement, et les valeurs de log(f[o.sub.2]) vont de -6,66 à -23,86 et de -9,88 à -25,18, respectivement, du champ tampon redox fayalite-magnetite-quartz au champ tampon redox magnetite-hematite, indiquant une source de magma oxydee qui pourrait avoir facilite l'enrichissement en Cu-Au. Les zircons des granitoïdes presentent des valeurs de [epsilon]Hf(t) allant de -0,75 à +2,33 et des âges modeles crustaux entre 0,9 Ga et 1,1 Ga. Les caracteristiques des isotopes de Lu-Hf et les grandes fourchettes definies par les valeurs de Mg#, Cr et Ni indiqueraient que les magmas des granitoïdes de Machangqing sont probablement derives de la fusion partielle d'une croûte inferieure juvenile, melanges avec des produits de fusion du manteau. Ces donnees, combinees à l'histoire geologique, la geochimie et les donnees isotopiques à l'echelle regionale, permettent de conclure au processus d'evolution suivant: durant le Cenozoïque, la collision continentale de l'Inde et de l'Asie a declenche la remontee d'asthenosphere chaude et son plaquage sous la croûte inferieure juvenile epaissie, ce qui a entraîne la formation de magmas mafiques et felsiques. Ces magmas ont remonte, se sont melanges, ont cristallise et ont forme les granitoïdes mineralises de Machangqing dans un milieu d'extension intracontinentale dans l'est du plateau tibetain. [Traduit par la Redaction] Mots-cles: datation U-Pb sur zircons par LA-ICP-MS, datation par Re-Os sur molybdenite, magma oxydant, gisement de Cu-Mo (Au) de Machangqing, ceinture de Jinshajiang - riviere Rouge, est du plateau tibetain., Introduction Porphyry Cu-(Mo-Au) deposits are among the most important types of economic deposits that account for a significant proportion of global Cu production (e.g., Cooke et al. 2005; Sillitoe 2010). [...]

The Xiarihamu Cu--Ni sulfide deposit is the second-largest Cu--Ni deposit in China, located in the Eastern Kunlun orogenic belt. However, despite previous study, the formation and evolution of this deposit remains a key unknown in the tectonic evolution of the Eastern Kunlun Orogenic Belt. Moreover, the petrogenesis of the ore-bearing rocks and the nature of ore genesis are the subjects of ongoing debate. Here, we present detailed field observations, petrology, zircon U--Pb geochronology, and Re--Os isotopic analyses to constrain the timing and genesis of the Xiarihamu Cu--Ni sulfide deposit. Sulfides from the massive ores yielded a Re--Os isotopic isochron age of 408 [+ or -] 11 Ma. Four samples from the ore-bearing Xiarihamu mafic-ultramafic intrusions yielded zircon U--Pb ages of 423.1 [+ or -] 2 Ma, 422.9 [+ or -] 3.1 Ma, 422.7 [+ or -] 2.3 Ma, and 422.6 [+ or -] 2.7 Ma, respectively, indicating that the ore formed during the Silurian. The calculated initial [.sup.187]Os/[.sup.188]Os ratio and [gamma]Os values ranged from 0.5109 to 0.8499 and from 311 to 584, respectively, indicating that crustal contamination played an extremely important role in triggering sulfide saturation. In combination with previous research, drill core observations and Re--Os data provide robust evidence for multiple pulses of magma replenishment throughout the process of ore genesis. Based on this evidence, the large-scale magmatic Cu--Ni mineralization in Xiarihamu likely occurred in a post-collisional setting related to tectonic slab breakoff. Key words: Xiarihamu Cu--Ni deposit, geochronology, Re--Os isotope, crustal contamination, Eastern Kunlun Orogenic belt. Le gisement sulfure de Cu--Ni de Xiarihamu, dans la ceinture orogenique du Kunlun oriental, est le deuxieme gisement de Cu--Ni en importance en Chine. Malgre certaines etudes anterieures, la formation et l'evolution de ce gisement dans le contexte de l'evolution tectonique de cette ceinture orogenique demeurent d'importantes inconnues. La petrogenese des roches mineralisees et la nature de la genese du minerai font en outre toujours l'objet de debats. Nous presentons des observations de terrain detaillees, ainsi que des donnees d'analyses petrologiques, de geochronologie U--Pb sur zircons et d'isotopes de Re--Os pour mieux definir l'age et la genese du gisement sulfure de Cu--Ni de Xiarihamu. Des sulfures provenant de minerais massifs ont donne un age d'isochrone pour les isotopes de Re--Os de 408 [+ or -] 11 Ma. Quatre echantillons d'intrusions mafiques--ultramafiques mineralisees de Xiarihamu ont donne des ages U--Pb sur zircons de 423,1 [+ or -] 2 Ma, 422,9 [+ or -] 3,1 Ma, 422,7 [+ or -] 2,3 Ma et 422,6 [+ or -] 2,7 Ma, respectivement, indiquant que le minerai s'est forme au Silurien. Les valeurs calculees du rapport [.sup.187]Os/[.sup.188]Os initial et de [gamma]Os vont de 0,5109 a 0,8499 et de 311 a 584, respectivement, indiquant que la contamination crustale a joue un role extremement important dans le declenchement de la saturation en sulfure. Combinees aux resultats de travaux anterieurs, des observations de carottes et des donnees de Re--Os fournissent des preuves robustes de plusieurs episodes d'apport de magma tout au long du processus de genese du minerai. A la lumiere de ces preuves, la mineralisation magmatique en Cu--Ni a grande echelle a Xiarihamu s'est vraisemblablement produite dans un milieu post-collision associe a la rupture d'une plaque tectonique subductee. [Traduit par la Redaction] Mots-cles : gisement de Cu--Ni de Xiarihamu, geochronologie, isotopes de Re--Os, contamination crustale, ceinture orogenique du Kunlun oriental., Introduction The Eastern Kunlun Orogenic Belt (EKOB) is an important metallogenic belt located in the western portion of the Central China Orogenic Belt. Large numbers of skarn, porphyry, and orogenic [...]

U-Pb geochronology was applied to a combination of magmatic and hydrothermal minerals to help constrain the timing of emplacement of three units in the Mount Douglas Granite (MDG) and reveal their association with a complex mineralized hydrothermal system containing endogranitic Sn-W-Mo-Zn-Bi-U-bearing greisen/sheeted veins within the pluton. Magmatic monazite and zircon U-Pb ages obtained by LA-ICP-MS overlap at 368 Ma, recording a Late Devonian crystallization age for the MDG. Although discrimination, outside analytical error, of sequential pulses of magmatism is beyond the resolution of LA-ICP-MS U-Pb geochronology, geochemical variations of monazite accompanied by previous whole-rock geochemical analyses support a progressive fractional crystallization process starting from a parental magma (Dmd1), leading to the generation of Dmd2, and finally Dmd3 as the most fractionated unit. Hydrothermal uraninite, cassiterite, and monazite, collected from endogranitic greisen/sheeted veins, reveal evidence for syn-magmatic-related mineralization and a longer-lived post-magmatic hydrothermal system. The first stage is recorded by concordant uraninite dates at 367 [+ or -]3 Ma and by an inverse isochron lower intercept of 362[+ or -]8Mafor cassiterite. In contrast, hydrothermal monazite crystallized over a wider range of ages from 368 to 344 Ma, demonstrating post-magmatic hydrothermal activity within the MDG. These magmatic and hydrothermal ages combined with the geochemical signature of the MDG are similar to those documented for the nearby Mount Pleasant Sn-W-Mo-Bi-In granite-related deposit, which suggests that the two mineralizing systems occur at different levels of the same magmatic system. Key words: laser ablation ICP-MS U-Pb geochronology, monazite, zircon, uraninite, cassiterite, Sn-W-Mo-Zn-Bi-U-bearing Mount Douglas Granite, New Brunswick. La geochronologie U-Pb a ete appliquee a une combinaison de mineraux magmatiques et hydrothermaux pour tenter d'etablir le moment de la mise en place de trois unites du granite du mont Douglas (GMD) et de determiner leur association a un systeme hydrothermal mineralise complexe contenant des greisen/filons en nappes endogranitiques a Sn-W-Mo-Zn-Bi-U dans le pluton. Les ages U-Pb sur monazite et zircon granitiques obtenus par LA-ICP-MS se chevauchent a 368 Ma, temoignant d'une cristallisation d'age devonien tardif pour le GMD. Bien que la discrimination, en dehors de l'erreur analytique, d'episodes sequentiels de magmatisme depasse la capacite de resolution de la geochronologie U-Pb par LA-ICP-MS, les variations geochimiques de la monazite combinees a des analyses geochimiques sur roche totale anterieures appuient l'interpretation d'un processus de cristallisation fractionnee graduel debutant par un magma parental (Dmd1), menant a la production de Dmd2 et, finalement, de Dmd3, l'unite la plus fractionnee. De l'uraninite, de la cassiterite et de la monazite hydrothermales, prelevees de greisen/filons en nappes endogranitiques, fournissent des preuves d'une mineralisation d'affinite synmagmatique et d'un systeme hydrothermal postmagmatique plus perenne. La premiere etape se reflete dans des ages sur uraninite concordants de 367 [+ or -] 3 Ma et dans le point d'intersection inferieur d'un isochrone inverse a 362 [+ or -]8 Ma pour la cassiterite. En comparaison, la cristallisation de la monazite hydrothermale definit une plus grande fourchette d'ages allant de 368 a 344 Ma, ce qui demontre une activite hydrothermale postmagmatique a l'interieur du GMD. Ces ages magmatiques et hydrothermaux, combines a la signature geochimique du GMD, sont semblables a ceux qui sont documentes pour le gisement de Sn-W-Mo-Bi-In associe a du granite de Mount Pleasant, situe a proximite, donnant a penser que les deux systemes mineralisateurs se situent a differents niveaux d'un meme systeme magmatique. [Traduit par la Redaction] Mots-cles: geochronologie U-Pb par ICP-MS avec ablation au laser, monazite, zircon, uraninite, cassiterite, granite a Sn-W-Mo-Zn-Bi-U du mont Douglas, Nouveau-Brunswick., Introduction Three units of the highly evolved Mount Douglas Granite (MDG) that were previously mapped in detail by McLeod (1990; Figs. 1 and 2) are a cogenetic group derived from [...]

Subduction zone processes are challenging to study because of the rarity of good exposures and the complexity of rock relationships within accretionary prisms. We report the results of field mapping and petrographic, geochemical, and geochronological analyses of the McHugh Complex accretionary prism melange in south-central Alaska that was recently exposed due to retreat of the Nelchina Glacier. Our new mapping and analyses of the melange, as well as adjacent Talkeetna arc intrusives, suggests that the previously mapped trace of the Border Ranges fault should shift northward in this location. Detailed petrographic analysis places this melange exposure with the Potter Creek assemblage of the McHugh Complex. Blocks of pillow lavas within the melange have both mid-ocean ridge basalt and intra-plate geochemical affinities, attesting to the complex relations of subduction-zone inputs in an alternating erosive--accretionary margin. A new zircon U-Pb age and geochemical analyses of a set of felsic dikes that cross-cut the accretionary sequence provide constraints on the regional tectonic evolution, including near-trench plutonism associated with the migration of a subducting spreading ridge along the southern Alaska margin during the Paleocene--Eocene. The McHugh section and cross-cutting dikes in this location are pervasively hydrothermally altered, which we attribute to elevated temperatures related to ridge subduction. Late-stage motion along the Border Ranges fault system, which is also recorded in the area, may also have contributed to the widespread alteration. Our data indicate that the Talkeetna volcanic arc and associated accretionary prism sediments were in their current configuration by 55 Ma. Key words: McHugh Complex, melange, Chugach terrane, southern Alaska, Talkeetna arc. Les processus associes aux zones de subduction sont difficiles a etudier en raison de la rarete de bons affleurements et de la complexite des relations entre les roches au sein de prismes d'accretion. Nous faisons etat des resultats de travaux de cartographie de terrain et d'analyses petrographiques, geochimiques et geochronologiques du melange de prisme d'accretion du complexe de McHugh, dans le centre-sud de l'Alaska, recemment expose par le retrait du glacier Nelchina. La nouvelle cartographie et les nouvelles analyses du melange, ainsi que des roches intrusives attenantes de l'arc de Talkeetna, donnent a penser que la trace cartographiee anterieurement de la faille des Border Ranges devrait se deplacer vers le nord en cet endroit. L'analyse petrographique detaillee place cette exposition du melange avec l'assemblage de Potter Creek du complexe de McHugh. Des blocs de lave a coussins dans le melange ont des affinites geochimiques avec du basalte de dorsale medio-oceanique et intraplaque, ce qui temoigne des relations complexes des apports de zone de subduction dans une marge alternant entre l'erosion et l'accretion. Un nouvel age U-Pb sur zircons et des analyses geochimiques d'un ensemble de dykes felsiques recoupant la sequence d'accretion permettent de preciser l'evolution tectonique regionale, dont du plutonisme proximal a une fosse associe a la migration d'une dorsale d'expansion en subduction le long de la marge sud de l'Alaska au Paleocene--Eocene. La coupe de McHugh et les dykes discordants dans cette localite temoignent d'une alteration hydrothermale penetrante que nous attribuons a des temperatures elevees associees a la subduction d'une dorsale. Un deplacement tardif le long du systeme de la faille des Border Ranges, qui est egalement preserve dans la region, pourrait aussi avoir contribue a l'alteration repandue. Nos donnees indiquent que la configuration actuelle de l'arc volcanique de Talkeetna et des sediments de prisme d'accretion associes etait deja etablie a 55 Ma. [Traduit par la Redaction] Mots-cles: complexe de McHugh, melange, terrane de Chugach, sud de l'Alaska, arc de Talkeetna., Introduction Arc--forearc relationships are difficult to study but are key to understanding processes that contribute to continental growth. Active margins are offshore and underwater, potentially buried by sediment. Ancient accretionary [...]

The geochemistry and Sr-Nd isotope, zircon U-Pb, and zircon Hf isotope compositions are reported for monzogranites and granodiorites from the Hazhu area in the northern Beishan orogen, northwestern China. Zircon U-Pb dating yielded ages of 270.1 [+ or -] 1.1 and 277.4 [+ or -] 1.2 Ma for the monzogranites and 263.6 [+ or -] 1.2 and 262.2 [+ or -] 1.1 Ma for the granodiorites. These monzogranites and granodiorites are metaluminous to weakly peraluminous I-type and belong to mid-K calc-alkaline and high-K calc-alkaline series. They exhibit high [Mg.sup.#] values and moderate degrees of differentiation (D.I. = 70.7-88.1). They are enriched in large-ion lithophile elements and light rare earth elements and depleted in high field strength elements. They show high [([.sup.87]Sr/[.sup.86]Sr).sub.i] ratios of 0.6995-0.7070 and high [[epsilon].sub.Nd](t) values of 4.37-5.70 with Nd model ages ([T.sub.DM]) of 522-789 Ma, suggesting a juvenile crustal origin. Furthermore, their [[epsilon].sub.Hf](t) values are all positive, and Hf isotopic crustal model ages ([T.sup.C.sub.DM] = 394-1097 Ma) also indicate a juvenile crustal origin. According to the data obtained in this study and other regional geological data acquired recently, the Hazhu granitoids were derived from common sources of melting from the Neoproterozoic to late Paleozoic juvenile crusts. The younger intrusions (granodiorites) are more basic, likely as a result of more juvenile lower crust being melted along with asthenospheric upwelling, which led to the addition of more basic components. These granitoids formed in a post-collisional setting. The tectonic regime transformed from an arc-related compressional setting to post-collisional extension, likely as a result of lithospheric extension and thinning in response to oceanic lithospheric delamination. These granitoids in the northern Beishan orogen were probably emplaced in a post-collisional extensional setting and suggest vertical continental crustal growth in the southern Central Asian Orogenic Belt. Key words: northern Beishan orogen, Early--Middle Permian, tectonic setting, zircon U-Pb dating, Sr-Nd isotopes, zircon Hf isotopes. Nous faisons etat de donnees geochimiques et des compositions d'isotopes de Sr-Nd, et de U-Pb et Hf dans les zircons pour des monzogranites et granodiorites de la region de Hazhu, dans l'orogene de Beishan septentrional (nord-ouest de la Chine). La datation U-Pb sur zircons donne des ages de 270,1 [+ or -] 1,1 Ma et 277,4 [+ or -] 1,2 Ma pour les monzogranites et 263,6 [+ or -] 1,2 Ma et 262,2 [+ or -] 1,1 Ma pour les granodiorites. Ces monzogranites et granodiorites sont metalumineux a legerement hyperalumineux de type I et font partie de la serie calcoalcaline a teneurs moyennes a elevees en K. Ils presentent des valeurs de [Mg.sup.#] elevees et des degres de differenciation intermediaires (ID = 70,7-88,1). Ils sont enrichis en elements lithophiles a grand rayon ionique et en terres rares legeres et appauvris en elements a forte liaison atomique. Ils presentent des rapports [([.sup.87]Sr/[.sup.86]Sr).sub.i] eleves de 0,6995-0,7070, ainsi que des valeurs de [[epsilon].sub.Nd](t) elevees de 4,37-5,70 avec des ages modeles Nd ([T.sub.DM]) de 522-789 Ma, ce qui indiquerait une origine dans la croute juvenile. Leurs valeurs de [[epsilon].sub.Hf](t) sont en outre toutes positives et les ages modeles de la croute bases sur les isotopes de Hf ([T.sup.C.sub.DM] = 394-1097 Ma) indiquent egalement une origine dans la croute juvenile. Au vu des donnees obtenues dans la presente etude et d'autres donnees geologiques regionales recentes, les granitoides de Hazhu proviennent de sources communes de fusion de croutes juveniles d'age neoproterozoique a paleozoique tardif. Les intrusions plus jeunes (granodiorites) sont plus basiques, probablement en raison de la fusion d'une croute plus juvenile accompagnee d'une remontee asthenospherique, qui a mene a l'ajout de composants plus basiques. Ces granitoides se sont formes dans un milieu post-collision. Le regime tectonique est passe d'un milieu de compression associe a un arc a un milieu d'extension post-collision, probablement en raison de l'extension et de l'amincissement lithospheriques decoulant de la delamination de la lithosphere oceanique. Ces granitoides dans le nord de l'orogene de Beishan se sont probablement mis en place dans un milieu d'extension post-collision et temoigneraient de la croissance verticale de la croute dans le sud de la ceinture orogenique d'Asie centrale. [Traduit par la Redaction] Mots-cles: nord de l'orogene de Beishan, Permien precoce a intermediaire, milieu tectonique, datation U-Pb sur zircons, isotopes de Sr-Nd, isotopes de Hf dans les zircons., Introduction The Central Asian Orogenic Belt (CAOB), located among the Eastern Europe, Siberia, Tarim, and North China plates (Fig. 1a), and which evolved from the late Mesoproterozoic (Kroner et al. [...]

Controversies exist regarding the mechanismofformationofbasins locatedonthe continental marginof South China as well as when they formed. It was ascertained based on clastic petrology, geochemical analysis, and zircon U--Pb dating that the sedimentary provenances in the eastern Guangdong Basin are mainly felsic igneous rocks from the late Early Jurassic to the Middle Jurassic. The late Early Jurassic Qiaoyuan Formation mainly shows major age peaks atapproximately 238 Ma, 259 Ma, and 1858 Ma, and the Middle Jurassic Tangxia Formation shows major age peaks at approximately 169 Ma and 172 Ma. From the late Early Jurassic to the Middle Jurassic in the eastern Guangdong Basin, the source region changes from southwestern South China and southern South China to the eastern Nanling Range. It was determined by comparing the detrital zircon ages of the Qiaoyuan Formation and the Tangxia Formation with thoseofthe late Paleozoictoearly Mesozoic basins, and analyzing both the geochemical data and sedimentation, that the eastern Guangdong Basin changed from the basin-arc foreland basin of the late Early Jurassic to the back-arc extension basin of the Middle Jurassic. The changes in early Mesozoic detrital zircon age peaks indicate that the tectonic regime of the eastern Guangdong Basin ended the transformation from the Tethyan tectonic domain to the paleo-Pacific tectonic domain in the early Middle Jurassic (approximately 172 Ma). Key words: eastern Guangdong Basin, late Early Jurassic to Middle Jurassic, provenances, tectonic regime transformation, zircon U--Pb dating. Des controverses persistent quant au mecanisme de formation de bassins situes sur la marge continentale de la Chine meridionale, ainsi qu'au moment de leur formation. Il a ete etabli, sur la base de la petrologie, l'analyse geochimique et la datation U--Pb sur zircons de depots clastiques que les sources de sediments dans le bassin de Guangdong oriental sont principalement des roches ignees felsiques d'age jurassique precoce tardif a jurassique moyen. La Formation de Qiaoyuan du Jurassique precoce tardif produit principalement de grands pics d'ages vers 238 Ma, 259 Ma et 1858 Ma, et la Formation de Tangxia du Jurassique moyen donne de grands pics d'ages vers 169 Ma et 172 Ma. Du Jurassique precoce tardif au Jurassique moyen dans le bassin de Guangdong oriental, la region source passe du sud-ouest et du sud de la Chine meridionale a la chaine de Nanling orientale. Il est determine, en comparant les ages de zircons detritiques des Formations de Qiaoyuan et de Tangxia a ceux des bassins d'age paleozoique tardif a mesozoique precoce et en analysant les donnees geochimiques et la sedimentation, que le bassin de Guangdong oriental est passe d'un bassin d'avant-pays d'un systeme arc-bassin au Jurassique precoce tardif a un bassin d'extension d'arriere-arc au Jurassique moyen. L'evolution des pics d'ages de zircons detritiques du Mesozoique precoce indique queleregime tectonique danslebassindeGuangdong orientalacloslatransformationdudomaine tectonique tethysien en un domaine tectonique paleopacifique au Jurassique moyen precoce (vers 172 Ma). [Traduit par la Redaction] Mots-cles : bassin de Guangdong oriental, Jurassique precoce tardif--Jurassique moyen, provenances, transformation du regime tectonique, datation U--Pb sur zircons., Introduction The main geotectonic outline of South China and even eastern China is controlled by the Indosinian and Yanshan movements (Wang and Zhou 2006; He et al. 2007; Z.H. Li [...]

Paleogene sediments of the Huntingdon Formation, a correlative to the Chuckanut Formation of neighbouring Washington State, USA, are exposed in the Greater Vancouver area, British Columbia, Canada. Palynology and plant macrofossils suggest the Kanaka Creek section is Paleocene rather than Eocene in age. Detrital zircon dating is less decisive, yet indicates the Kanaka rocks are no older than Maastrichtian. Analyses of plant macro- and micro-fossils suggest an early to middle Paleocene age for the Kanaka fossil flora. Paleocene indicators include macrofossils such as Platanus bella, Archeampelos, Hamamelites inequalis, and Ditaxocladus, and pollen taxa such as Paraalnipollenites, Triporopollenites mullensis, and Duplopollis. Paleogene taxa such as Woodwardia maxonii, Macclintockia, and Glyptostrobus dominate the flora. Fungal spores including the Late Cretaceous Pesavisparva and the Paleogene Pesavis tagluensis are notable age indicators. Physiognomy of 41 angiosperm leaf morphotypes from Kanaka Creek yields mean annual temperatures in the microthermal to lower mesothermal range (11.2 [+ or -] 4.3 to 14.6 [+ or -] 2.7 [degrees]C from leaf margin analysis; 14.8 [+ or -] 2.1 [degrees]C from Climate Leaf Analysis Multivariate Program), with mild winters (cold month mean temperature 3.9 [+ or -] 3.4 [degrees]C). Paleoclimate was cooler than the upper Paleocene and Eocene members of the Chuckanut Formation. Mean annual precipitation is estimated at ~140 cm with large uncertainties. The Kanaka paleoflora is reconstructed as a mixed conifer-broadleaf forest, sharing common taxa with other western North American Paleocene floras and growing in a temperate moist climate. Kanaka Creek is a rare coastal Paleocene plant locality that provides new insights into coastal vegetation and climate prior to the Paleocene-Eocene Thermal Maximum. Key words: Paleocene, paleobotany, palynology, paleoclimate, Huntingdon Formation, Kanaka Creek. Résumé : Des sédiments paléogènes de la Formation d'Huntingdon, une formation corrélative de la Formation de Chuckanut de l'État voisin de Washington (États-Unis), sont exposés dans la région de Vancouver (Colombie-Britannique, Canada). La palynologie et les macrofossiles de plantes donnent à penser que la coupe de Kanaka Creek est d'âge paléocène plutôt qu'éocène. Si la datation de zircons détritiques est moins concluante, elle indique toutefois que l'âge des roches de Kanaka n'est pas plus vieux que le Maastrichtien. Des analyses de macro- et microfossiles de plantes indiqueraient un âge paléocène précoce à moyen pour la flore fossile de Kanaka. Parmi les indicateurs paléocènes figurent des macrofossiles tels que Platanus bella, Archeampelos, Hamamelites inequalis et Ditaxocladus et des taxons de pollen tels que Paraalnipollenites, Triporopollenites mullensis et Duplopollis. Des taxons paléogènes comme Woodwardia maxonii, Macclintockia et Glyptostrobus sont dominants dans la flore. Des spores fongiques comprenant Pesavis parva d'âge crétacé tardif et Pesavis tagluensis d'âge paléogène sont des indicateurs d'âge notables. L'analyse physionomique de 41 morphotypes de feuilles d'angiosperme de Kanaka Creek produit des températures annuelles moyennes dans une fourchette allant de microthermique à mésothermique inférieure (de 11,2 [+ ou -] 4,3 [degré]C à 14,6 [+ ou -] 2,7 [degré]C obtenues de l'analyse de bordures de feuille, LMA; 14,8 [+ ou -] 2,1 [degré]C obtenue de CLAMP), avec des hivers doux (température moyenne des mois froids : 3,9 [+ or -] 3,4 [degré]C). Le paléoclimat était plus frais que ce qu'enregistrent les membres paléocène supérieur et éocène de la Formation de Chuckanut. Les précipitations annuelles moyennes sont estimées à ~140 cm, avec d'importantes incertitudes. La reconstitution de la paléoflore de Kanaka donne une forêt mixte à conifères-caducifoliés ayant des taxons en commun avec d'autres flores paléocènes de l'ouest de l'Amérique du Nord et croissant dans un climat tempéré humide. Kanaka Creek est une rare localité de plantes paléocènes côtières qui fournit de nouveaux renseignements sur la végétation et le climat côtiers avant le maximum thermique du passage Paléocène/Éocène. [Traduit par la Rédaction] Mots-clés : Paléocène, paléobotanique, palynologie, paléoclimat, Formation d'Huntingdon, Kanaka Creek., Introduction The main objectives of this paper are to assess the age assignment and paleoclimate of the Kanaka Creek paleoflora, southwestern British Columbia, Canada, using plant macrofossils as well as [...]

Late Mesozoic granitic rocks are widely distributed in the Sulu orogenic belt, but the source, tectonic affinity, and associated geodynamic setting that produced the respective magmas remain controversial. To provide insights into these issues, we present field-based petrological, whole-rock major and trace element and Sr-Nd isotope geochemical, zircon U-Pb dating, and Lu-Hf isotope studies on two types of granite porphyry dykes that are newly recognized from the central Sulu belt. U-Pb dating of magmatic zircons from both types yields consistent ages that vary between 124 [+ or -] 2 and 118 [+ or -] 2 Ma, constraining the timing of intrusion as Early Cretaceous. The granitic rocks have high-K calc-alkaline peraluminous compositions with low Mg# values and are characterized by fractionated rare earth element patterns with strong depletion in high field strength elements. Compared with type I of the granite porphyry dykes, type II exhibits higher Si[O.sub.2] but slightly lower [Na.sub.2]O and [K.sub.2]O abundances, contains higher Rb/Sr and [.sup.87]Sr/[.sup.86]Sr ratios, and shows more pronounced negative Eu, Sr, and Ba anomalies. Both types I and II have high initial [.sup.87]Sr/[.sup.86]Sr ratios of 0.709-0.711 and negative [[epsilon].sub.Nd](t) values of-19.8 to -18.4. The magmatic zircons possess negative [[epsilon].sub.Hf](t) values of-29.1 to -20.8, with mostly Neoarchean Hf model ages of 3001-2478 Ma. These features, together with the presence of Neoproterozoic inherited zircons, indicate that the two types of granite porphyries successively crystallized from a joint granite magma that derived from partial melting of the continental crust of the Yangtze Craton. Therefore, an interrelationship between the granite porphyry dykes and massive magmatic granitoids from adjacent regions in the Sulu belt may be documented, recording evidence of a joint ancient crustal reworking and recycling in a fossilized continental subduction zone during the Early Cretaceous. Key words: collisional orogen, paleo-Pacific plate subduction, granite porphyry, U-Pb zircon geochronology, Sulu orogenic belt. Des roches granitiques d'age mesozoique tardif sont largement repandues dans la ceinture orogenique de Sulu, mais la source, l'affinite tectonique et le contexte geodynamique associe qui ont produit leurs magmas respectifs demeurent controverses. Afin de jeter un nouvel eclairage sur ces questions, nous presentons les resultats d'analyses geochimiques des elements majeurs et en traces sur roche totale et des isotopes de Sr-Nd et de Lu-Hf, et de la datation U-Pb sur zircons pour deux types de dykes de granite porphyrique nouvellement decouverts dans la partie centrale de la ceinture de Sulu. La datation U-Pb sur zircons magmatiques des deux types de granite donne des ages coherents allant de 124 [+ or -] 2 a 118 [+ or -] 2 Ma, ce qui fixe le moment de leur intrusion au Cretace precoce. Les roches granitiques ont des compositions hyperalumineuses calco-alcalines riches en K avec de faibles Mg#, et elles sont caracterisees par des spectres de terres rares fractionnes montrant un appauvrissement marque des elements a forte liaison atomique. Comparativement au premier type de dykes de granite porphyrique, le deuxieme type presente de plus fortes teneurs en Si[O.sub.2], mais des concentrations de [Na.sub.2]O et [K.sub.2]O legerement plus faibles, des rapports Rb/Sr et [.sup.87]Sr/[.sup.86]Sr plus eleves et des anomalies negatives plus prononcees de Eu, Sr et Ba. Les deux types presentent des rapports initiaux de [.sup.87]Sr/[.sup.86]Sr eleves de 0,709-0,711 et des valeurs negatives de [[epsilon].sub.Nd](t) allant de -19,8 a -18,4. Les zircons magmatiques ont des [[epsilon].sub.Hf](t) negatifs de -29,1 a -20,8, et des ages modeles Hf principalement neoarcheens de 3001 Ma - 2478 Ma. Ces caracteristiques, combinees a la presence de zircons neoproterozoiques herites, indiquent que les deux types de porphyre granitique ont cristallise successivement d'un meme magma granitique derive de la fusion partielle de la croute continentale du craton du Yangzi. Une interrelation entre les dykes de granite porphyrique et des granitoides magmatiques massifs de regions attenantes dans la ceinture de Sulu pourrait ainsi etre documentee, qui temoigne de leur remaniement crustal et de leur recyclage communs dans une zone de subduction continentale fossilisee durant le Cretace precoce. [Traduit par la Redaction] Mots-cles: orogene de collision, subduction de la plaque paleo-Pacifique, porphyre granitique, geochronologie U-Pb sur zircons, ceinture orogenique de Sulu., Introduction Migration of granitic magmas from their source regions in the deep orogenic crust to sites of accumulation and emplacement at shallower crustal levels is an important process for mass [...]

Our paper reports the detrital zircon record from Late Devonian to late Carboniferous foreland basin deposits in the Rheno-Hercynian (RH) Variscides of Germany. Together with a review of petrography and detrital mineral ages from the literature, the data permit to reconstruct accretion and exhumation along the RH active margin. From Frasnian to latest Carboniferous, the main source (now eroded) was a north-Armorican microcontinent (Franconia) with magmatic rocks representing late Neoproterozoic arc or back-arc, Cambro-Ordovician rift and Silurian--Early Devonian subduction of the Rheic ocean and (or) RH rifting. At ca. 380 Ma, detrital magmatic zircons combined with high- to medium-pressure mica and detrital glaucophane suggest the existence of a paired metamorphic belt at the RH tectonic front. From the Visean onwards, zircons reveal younging of granitoid debris from ca. 380-360 Ma in Late Devonian sediments to ca. 320-300 Ma in the Westphalian C-D and Stephanian. Greywackes of the Namurian A record a change from dominant magmatic clasts toward meta-arenites associated with Baltoscandian zircons, which document accretion to and exhumation from the base of the orogenic wedge. Their source must be sought in metamorphosed Devonian sandstones of the type presently encountered in parts of the active margin crystallines (Mid-German Crystalline High), but in eroded higher units. Basal accretion implies heating of the lower plate beyond the brittle--ductile boundary and supports the model of a high-temperature regime before and during Variscan collision. Palinspastic restoration of the estimated volume of recycled material yields >100 km of distal shelf deposits lost in the process, which adds to the known shortening of the RH basin. The Variscan geology of southwestern England and southern Portugal and provenance studies in those areas are compatible with a geodynamic evolution similar to that in Germany. Key words: detrital zircon, U--Pb laser ICP-MS, foreland basin deposits, Rheno-Hercynian belt, Variscides. Nous rendons compte du registre des zircons detritiques de depots de bassin d'avant-pays d'ages devonien tardif a carbonifere tardif dans la zone rheno-hercynienne (RH) de la chame varisque d'Allemagne. Combinees a un examen de la petrographie et des ages de mineraux detritiques publies, les donnees permettent de reconstituer l'accretion et l'exhumation le long de la marge RH active. Du Frasnien a la fin du Carbonifere, la source principale (aujourd'hui erodee) etait un microcontinent nord-armoricain (la Franconie) avec des roches magmatiques representant un arc ou arriere-arc d'age neoproterozoique tardif, un rift cambro-ordovicien et la subduction du Silurien au Devonien precoce de l'ocean Rheique ou un rifting RH. Vers 380 Ma, des zircons magmatiques detritiques combines a des micas de haute a moyenne pression et du glaucophane detritique indiquer-aient l'existence d'une ceinture metamorphique jumelee au front tectonique RH vers 380 Ma. A partir du Viseen, les zircons revelent un rajeunissement des debris de granitoide a partir d'environ 380-360 Ma dans des sediments d'age devonien tardif a environ 320-300 Ma dans le Westphalien C-D et le Stephanien. Des grauwackes du Namurien A enregistrent le passage de clastes principalement magmatiques a des meta-arenites associees a des zircons baltoscandiens, qui documentent l'accretion a la base du biseau orogenique et l'exhumation subsequente. Leur source doit se trouver dans des gres devoniens metamorphises semblables a ceux qui se trouvent actuellement dans les roches cristallines de la marge active (ride cristalline medio-allemande), mais dans des unites plus hautes erodees. L'accretion basale signifie que la plaque inferieure a ete chauffee au-dela de la limite cassant--ductile et appuie le modele d'un regime de haute temperature avant et durant la collision varisque. La reconstitution palinspatique du volume estime de materiau recycle donne >100 km de depots de plateforme distale evacues durant le processus, ce qui vient s'ajouter au raccourcissement connu du bassin RH. La geologie varisque du sud-ouest de l'Angleterre et du sud du Portugal et des etudes de provenance dans ces regions sont compatibles avec une evolution geodynamique semblable a celle observee en AUemagne. Mots-cles : zircon detritique, analyse U--Pb par ICP-MS avec ablation au laser, depots de bassin d'avant-pays, ceinture rhenohercynienne, chame varisque., Introduction Rationale The Rheno-Hercynian (RH) Variscides (Portugal, southwestern England, Germany, Poland, Turkey) were formed from the infill of the narrow RH ocean. Closure of that ocean is documented, especially in [...]

Demolding is a necessary process in polymer micro molding, which requires energy for fracture of the bonds between the mold and the polymer. This often leads to structural defects due to an inappropriate combination of process parameters, including demolding temperature, embossing force or injection pressure, separation rate, and separation mode. In this article, we focus on the theoretical analysis and experimental optimization of the process parameters for polymer micro-part demolding from a zirconium (Zr)-based bulk metallic glass mold. We developed a theoretical model to predict the demolding work, in which we considered the effects of sidewall friction combined with deformation and adhesion. We also optimized the parameters for the demolding process based on the Taguchi method. The experimental results showed that the embossing force and the separation mode had significant effects on the demolding work of hot embossing. We determined the optimum process parameters and found that with these parameters the demolding work could be decreased to 10.36 mJ in this case., INTRODUCTION Plastic is a favorable material for fabricating microfluidic devices due to its low cost, available molding technologies, as well as wide range of mechanical properties and amenability to mass [...]

Evidence for exotic terranes in the central Appalachian Piedmont Province is fragmented between central Virginia, northern Maryland, and southeastern Pennsylvania. Here we present laser ablation-inductively coupled plasma mass spectrometry data from detrital zircon that support the presence of an exotic terrane in this region. U-Pb dating of detrital zircon from new samples of the Storck quartzite (central Virginia) and the Hoods Mill rocks (northern Maryland) confirms the presence of a major peak at ca. 630-610 Ma in these units. These ages are consistent with derivation from Gondwana, but not Ediacaran Laurentia. Further, modern [epsilon]Hf values of five of the ca. 670-580 Ma grains in these samples are inconsistent with derivation from the few plutons of this age in Ediacaran Laurentia. The Loch Raven Schist and a metasedimentary xenolith in the Wilmington Complex contain a smaller proportion of ca. 670-580 Ma grains than the Storck quartzite and the Hoods Mill rocks, but more such grains than in sediment derived from Ediacaran Laurentia, so we tentatively conclude that these two units also received sediment from Gondwana. Detrital zircon ages from the Piney Run Formation, Pleasant Grove Schist, Prettyboy Schist, and Wissahickon Formation allow sediment provenance solely in Ediacaran Laurentia. We also present new zircon spot U-Pb and Lu-Hf isotopic data from western Newfoundland plutons for comparison with these types of data from the detrital zircon. Intrusion ages of the Steel Mountain Anorthosite, Disappointment Hill Tonalite, and Round Pond Granite are 608 [+ or -] 12, 600 [+ or -] 8, and 590 [+ or -] 9 Ma, respectively. None of these units was derived entirely from the depleted mantle. Key words: zircon, radiogenic isotopes, Appalachians, exotic terrane, orogeny. Les preuves de la presence de terranes exotiques dans la province du piemont des Appalaches entre le centre de la Virginie, le nord du Maryland et le sud-est de la Pennsylvanie sont fragmentaires. Nous presentons des donnees de spectrometrie de masse a plasma induit couplee a l'ablation laser (LA-ICPMS) issues de zircons detritiques qui appuient l'interpretation de la presence d'un terrane exotique dans cette region. La datation U-Pb sur zircons detritiques issus de nouveaux echantillons de la quartzite de Storck (Virginie centrale) et des roches de Hoods Mill (nord du Maryland) confirme la presence d'un pic important vers 630-610 Ma dans ces unites. Ces ages concordent avec une provenance du Gondwana, mais non de la Laurentie ediacarienne. En outre, les valeurs de [epsilon]Hf modernes de cinq des grains d'environ 670-580 Ma dans ces echantillons ne concordent pas avec une provenance des quelques plutons de cet age en Laurentie ediacarienne. Le schiste de Loch Raven et un xenolite metasedimentaire du complexe de Wilmington renferment une plus faible proportion de grains d'environ 670-580 Ma que la quartzite de Storck et les roches de Hoods Mill, mais une proportion plus grande de ces grains que dans des sediments provenant de la Laurentie ediacarienne; nous concluons donc provisoirement que ces deux unites ont egalement recu des apports de sediments du Gondwana. Des ages de zircons detritiques de la Formation de Piney Run, du schiste de Pleasant Grove, du schiste de Prettyboy et de la Formation de Wissahickon permettent l'interpretation d'une provenance de sediments uniquement de la Laurentie ediacarienne. Nous presentons egalement de nouvelles donnees d'analyses isotopiques U-Pb et Lu-Hf ponctuelles sur zircons de plutons de l'ouest de Terre-Neuve a des fins de comparaison avec ces types de donnees provenant de zircons detritiques. Les ages d'intrusion de l'anorthosite de Steel Mountain, de la tonalite de Disappointement Hill et du granite de Round Pond sont de 608 [+ or -] 12 Ma, 600 [+ or -] 8 Ma et 590 [+ or -] 9 Ma, respectivement. Aucune de ces unites n'est derivee entierement du manteau appauvri. [Traduit par la Redaction] Mots-cles : zircon, isotopes radiogeniques, Appalaches, terrane exotique, orogenese., 1. Introduction Successive accretion of magmatic arcs and ribbon continents during Early Ordovician to Early Mississippian time caused pulses of orogeny in eastern Laurentia (van Staal et al. 2009; Pollock [...]

Spanning 2500 km along the western margin of North America are 780 Ma dykes, sills, and minor volcanic packages of the Gunbarrel Large Igneous Province. This study focuses on southern (northwestern United States) and central (northern British Columbia) Gunbarrel intrusions and metavolcanics rocks of the Irene and Huckleberry formation (Washington State). Southern Gunbarrel U--Pb ages range from 780 to 769 Ma and new U--Pb zircon dates for the Turah and Rogers Pass sills are 778.6 [+ or -] 0.7 and 778.7 [+ or -] 0.9 Ma, respectively. Southern Gunbarrel intrusions are medium- to coarse-grained diabases that are moderately evolved basaltic, continental tholeiites. Intrusions display negative Nb--Ta and positive Pb anomalies in normalized multielement plots, and [[epsilon].sub.Nd.sup.780] values vary from +3.6 to +1.5. The Irene and Huckleberry volcanic rocks are E-MORB in composition with higher [[epsilon].sub.Nd.sup.780] (+5 to +6) and likely represent partial melts of a mantle plume responsible for the Gunbarrel event. Assuming an Irene and Huckleberry parental magma, mixing models indicate that the southern Gunbarrel magmas were crustally contaminated, but local host rocks are not appropriate crustal contaminants. The modeling points to average upper crust as the crustal contaminant, with an [[epsilon].sub.Nd.sup.780] of approximately -2. This crustal contaminant likely resides on the craton impinged upon by the mantle plume. The remarkable geochemical homogeneity of Gunbarrel intrusions from the Yukon to Wyoming is best explained if primary, plume-derived E-MORB magmas were contaminated in large magma reservoirs near the plume centre and were then injected laterally into the crust 100s to 1000s of kilometres from the reservoir. Key words: Neoproterozoic, Gunbarrel Large Igneous Province, Large Igneous Province, geochemistry, isotopic composition, mantle sources. Répartis sur 2500 km le long de la bordure ouest de l'Amérique du Nord se trouvent des dykes, filons-couches et petits ensembles volcaniques de 780 Ma d'âge de la grande province ignée de Gunbarrel. L'étude porte sur les intrusions du sud (nord-ouest des États-Unis) et du centre (nord de la Colombie-Britannique) de la province de Gunbarrel et les roches métavolcaniques de la Formation d'Irene et Huckleberry (État de Washington). Les âges U--Pb pour le sud de la province de Gunbarrel vont de 780 à 769 Ma, et de nouveaux âges U--Pb sur zircons pour les filons-couches de Turah et Rogers Pass sont de 778,6 [+ or -] 0,7 et 778,7 [+ or -] 0,9 Ma, respectivement. Les intrusions du sud de la province de Gunbarrel sont des diabases à grains moyens à grossiers correspondant à des tholéites continentales basaltiques évoluées. Les intrusions présentent des anomalies négatives de Nb--Ta et positives de Pb dans des spectres multiéléments normalisés, et les valeurs de [[epsilon].sub.Nd.sup.780] vont de +3,6 à +1,5. Les roches volcaniques d'Irene et Huckleberry sont de type E-MORB, avec des valeurs de [[epsilon].sub.Nd.sup.780] plus élevées (+5 à +6) et représentent vraisemblablement des produits de la fusion partielle d'un panache mantellique à l'origine de l'épisode de Gunbarrel. Partant de l'hypothèse d'un magma parental d'Irene et Huckleberry, les modèles de mélange indiquent que les magmas du sud de la province de Gunbarrel ont fait l'objet d'une contamination crustale, bien que les roches encaissantes locales ne soient pas des contaminants crustaux convenables. La modélisation indiquerait qu'une croûte supérieure moyenne, présentant un [[epsilon].sub.Nd.sup.780] environs -2, serait la source de contamination crustale. Ce contaminant crustal se trouve vraisemblablement dans le craton sur lequel poussait le panache mantellique. L'homogénéité géochimique remarquable des intrusions de Gunbarrel du Yukon jusqu'au Wyoming s'explique le mieux par la contamination, dans de grands réservoirs de magma près du centre du panache, de magmas primaires de type E-MORB dérivés du panache, injectés ensuite latéralement dans la croûte à des centaines, voire des milliers de kilomètres du réservoir. [Traduit par la Rédaction] Mots-clés: Néoprotérozoïque, grande province ignée de Gunbarrel, grande province ignée, géochimie, composition isotopique, sources mantelliques., Introduction Spanning over 2500 km along the western margin of North America from the Yukon and Northwest Territories, Canada, to Montana, Wyoming, and Idaho, United States, are diabase dykes, sills, [...]

Accessory mineral thermometry and thermodynamic modelling are fundamental tools for constraining petrogenetic models of granite magmatism. U-Pb geochronology on zircon and monazite from S-type granites emplaced within a semi-continuous, whole-crust section in the Georgetown Inlier (GTI), NE Australia, indicates synchronous crystallisation at 1550 Ma. Zircon saturation temperature (T.sub.zr) and titanium-in-zircon thermometry (T.sub.(Ti-zr)) estimate magma temperatures of ~ 795 ± 41 °C (T.sub.zr) and ~ 845 ± 46 °C (T.sub.(Ti-zr)) in the deep crust, ~ 735 ± 30 °C (T.sub.zr) and ~ 785 ± 30 °C (T.sub.(Ti-zr)) in the middle crust, and ~ 796 ± 45 °C (T.sub.zr) and ~ 850 ± 40 °C (T.sub.(Ti-zr)) in the upper crust. The differing averages reflect ambient temperature conditions (T.sub.zr) within the magma chamber, whereas the higher T.sub.(Ti-zr) values represent peak conditions of hotter melt injections. Assuming thermal equilibrium through the crust and adiabatic ascent, shallower magmas contained 4 wt% H.sub.2O, whereas deeper melts contained 7 wt% H.sub.2O. Using these H.sub.2O contents, monazite saturation temperature (T.sub.mz) estimates agree with T.sub.zr values. Thermodynamic modelling indicates that plagioclase, garnet and biotite were restitic phases, and that compositional variation in the GTI suites resulted from entrainment of these minerals in silicic (74-76 wt% SiO.sub.2) melts. At inferred emplacement P-T conditions of 5 kbar and 730 °C, additional H.sub.2O is required to produce sufficient melt with compositions similar to the GTI granites. Drier and hotter magmas required additional heat to raise adiabatically to upper-crustal levels. S-type granites are low-T mushes of melt and residual phases that stall and equilibrate in the middle crust, suggesting that discussions on the unreliability of zircon-based thermometers should be modulated., Author(s): S. Volante [sup.1] [sup.2] [sup.4], W. J. Collins [sup.1], E. Blereau [sup.3], A. Pourteau [sup.1], C. Spencer [sup.1], N. J. Evans [sup.3], V. Barrote [sup.4] [sup.3], A. R. Nordsvan [...]

The Late Silurian to Late Devonian Saint George Batholith in southwestern New Brunswick is a large composite intrusion (2000 [km.sup.2]) emplaced into the continental margin of the peri-Gondwanan microcontinent of Ganderia. The batholith includes: (1) Bocabec Gabbro; (2) equigranular Utopia and Wellington Lake biotite granites; (3) Welsford, Jake Lee Mountain, and Parks Brook peralkaline granites; (4) two-mica John Lee Brook Granite; (6) Jimmy Hill and Magaguadavic megacrystic granites; and (6) rapakivi Mount Douglas Granite. New LA ICP-MS in situ analyses of six samples from the Saint George Batholith are as follows: (1) U-Pb monazite crystallization age of 425.5 [+ or -] 2.1 Ma for the Utopia Granite in the western part of the batholith (2) U-Pb zircon crystallization ages of 420.4 [+ or -] 2.4 Ma and 420.0 [+ or -] 3.5 Ma for two samples of the Utopia Granite from the central part of the batholith; (3) U-Pb zircon crystallization age of 418.0 [+ or -] 2.3 Ma for the Jake Lee Mountain Granite; (4) U-Pb zircon crystallization age of 415.5 [+ or -] 2.1 Ma for the Wellington Lake Granite; and (5) U-Pb monazite crystallization age of 413.3 [+ or -] 2.1 Ma for the John Lee Brook Granite. The new geochronological together with new and existing geochemical data suggest that the protracted magmatic evolution of the Late Silurian to Early Devonian plutonic rocks is related to the transition of the Silurian Kingston arc-Mascarene backarc system from an extensional to compressional tectonic environment during collision of the Avalonian microcontinent with Laurentia followed by slab break-off. Le batholite du Silurien tardif au Devonien tardif de Saint George dans le sud ouest du Nouveau Brunswick est une vaste intrusion composite (2 000 kilometres carres) qui s'est mise en place a l'interieur de la marge continentale du microcontinent perigondwanien de Ganderia. Le batholite englobe : (1) le gabbro de Bocabec; (2) les granites a biotite isogranulaire Utopia et du lac Wellington; (3) les granites hyperalcalins de Welsford, du mont Jake Lee et du ruisseau Parks Brook; (4) le granite a deux micas du ruisseau John Lee; (5) les granites macrocristallins de la colline Jimmy et de Magaguadavic; et (6) le granite rapakivi du mont Douglas. De nouvelles analyses par spectrometrie de masse a plasma induit couplee a l'ablation laser in situ de six echantillons provenant de Saint George ont revele ce qui suit : (1) une cristallisation survenue il y a 425,5 [+ or -] 2,1 Ma d'apres une datation U-Pb sur monazite, dans le cas du granite Utopia dans la partie occidentale du batholite; (2) des ages de cristallisation en vertu d'une datation U-Pb sur zircon de 420,4 [+ or -] 2,4 Ma et de 420,0 [+ or -] 3,5 Ma dans le cas de deux echantillons en provenance du granite Utopia dans le centre du batholite; (3) un age de cristallisation de 418,0 [+ or -] 2,3 Ma dans le cas du granite du mont Jake Lee, d'apres une datation U-Pb sur zircon; (4) un age de cristallisation de 415,5 [+ or -] 2,1 Ma obtenu par datation U-Pb sur zircon dans le cas du granite du lac Wellington; et (5) un age de cristallisation de 413,3 [+ or -] 2,1 Ma d'apres une datation U-Pb sur monazite, dans le cas du granite du ruisseau John Lee. Les nouvelles donnees geochronologiques conjuguees aux donnees geochimiques existantes laissent supposer que l'evolution magmatique prolongee de des roches plutoniques du Silurien tardif au Devonien precoce est apparentee a la transition de l'arc silurien de Kingston-arriere-arc de Mascarene d'un milieu tectonique de distension a un milieu de compression durant la collision du microcontinent avalonien avec Laurentia suivie d'une rupture par tranches., [Traduit par la redaction] INTRODUCTION The Silurian (Ludlovian to Pridolian) to Late Devonian (Famennian) Saint George Batholith in southwestern New Brunswick is a large composite intrusion (2000 [km.sup.2]) that was [...]

The Andean margin of the South American continent has been magmatically and tectonically active for over 330 million years. It is the type location where 'Cordilleran-type' magmatism and orogenesis are manifest. In Argentina and Chile, between the latitudes of 28° and 40° S, magmatism related to the Gondwanan 'Cordilleran-type' orogeny is reflected in a series of Carboniferous to Triassic intrusions. A comprehensive model exists for the petrogenesis of such magmas in Chile, however there is relatively little understanding of the nature and timing of Permo-Triassic magmatism in the Frontal Cordillera and Precordillera in Argentina. To address this, we present a new dataset of in situ zircon U-Pb, O and Hf isotopes from 15 felsic intrusions from Argentina. Zircon geochronology shows that magmatism in this region commenced at ca. 285 Ma and continued until ca. 250 Ma. Zircon O and Hf isotopes suggest that the oldest Permian magmas were derived from young supracrustal sources, with elevated [delta].sup.18O (~ 8.5 to 7.5â°) and negative [epsilon].sub.Hf values (~ - 1 to - 3 [epsilon].sub.Hf). The emplacement of these magmas was coeval with the formation of mantle-derived magmas characterised by mantle-like [delta].sup.18O (~ 6.0 to 5.5â°) and moderately positive [epsilon].sub.Hf values (~ 4 to 1 [epsilon].sub.Hf). As magmatism continued, transitional isotope signatures became predominant as melts of these disparate sources interacted and hybridised. It is proposed that under a compressional regime, mantle-derived magmas were halted in the lower continental crust, where they exchanged heat and volatiles with an older fertile lithosphere to generate melts from supracrustal sources. A shift in the stress regime at ca. 285 Ma permitted both crustally derived and juvenile mantle-derived magmas to exploit newly formed conduits to rise into the upper crust. A regional compilation of zircon O and Hf isotopes from felsic igneous rocks reveals a coherent secular trend over ~ 100 million years, where the oldest magmatism exhibits a dominant supracrustal component and younger magmas progressively (over 50 Ma) transition towards juvenile mantle-like isotopic compositions. This new dataset from Argentina fills a significant gap in the previous regional models between 285 and 250 Ma and documents the isotopic response of magmas produced in back-arc regions to a transition between compression and extensional/neutral stress regimes. These results give insight into the generation of new, or recycling of, continental crust in a back-arc setting and how the transition from compression to extension is imperative for ore-forming magmas to reach the upper crust., Author(s): Gregory H. Poole [sup.1] [sup.2], Anthony I. S. Kemp [sup.1], Steffen G. Hagemann [sup.1], Marco L. Fiorentini [sup.1] [sup.2], Heejin Jeon [sup.3] [sup.7], Ian S. Williams [sup.4], Eduardo O. [...]

In situ LA-ICP-MS U-Pb geochronology has been performed on apatite and zircon within thermally recrystallized clast-laden and clast-poor impact melt rocks from the Brent impact structure. A total of 377 laser analyses on 120 impact melt-grown (n = 9) and impact-recrystallized zircon grains (n = 111) were obtained, from which a concordia age of 452.8 ± 2.7 Ma (MSWD 0.57, n = 11), and a weighted average mean .sup.206Pb/.sup.238U age of 453.2 ± 2.9 Ma (MSWD 0.60) (n = 11) are calculated. A total of 300 laser analyses from 100 relict apatite grains were obtained, with an unanchored regression through all data yielding a lower intercept age of 453.2 ± 6.0 Ma (MSWD 5.8, n = 300), that overlaps within error of zircon. .sup.207Pb/.sup.206Pb ratios obtained from feldspar clasts within clast-laden impact melt retain the same initial Pb composition as the target rocks from which they are derived, while feldspars that crystallized from impact melt have .sup.207Pb/.sup.206Pb ratios indicative of isotopic re-equilibration between basement lithologies of two different ages. A similar variability in .sup.207Pb/.sup.206Pb is recorded by apatite. This provides evidence for the involvement of Neoproterozoic Lake Nipissing alkaline suite, as well as Mesoproterozoic Grenville gneisses in the production of impact melt at Brent. Recrystallized apatite grains exhibit enrichments in light rare earth elements (LREEs) along neoblast grain boundaries, indicative of trace element substitution and phase precipitation during impact-induced recrystallization. An age of 452.8 ± 2.7 Ma from zircon and 453.2 ± 6.0 Ma from apatite places the impact event in the Late Ordovician, at or near the Sandbian-Katian boundary, confirming Brent's involvement in the Middle to Late Ordovician crater cluster event-a period of enhanced impactor flux to Earth related to the L-Chondrite parent body disruption., Author(s): Maree McGregor [sup.1] [sup.2], Michael R. Dence [sup.3], Christopher R. M. McFarlane [sup.2], John G. Spray [sup.1] Author Affiliations: (1) grid.266820.8, 0000 0004 0402 6152, Planetary and Space Science [...]

We applied interface-controlled kinetics, including interface-controlled Ostwald ripening and non-hydrostatic dissolution-precipitation, to metamorphic zircon and phengite growth in a high-pressure (high-P) metamorphic complex. This kinetic modeling yields the growth duration of metamorphic zircon, based on the assumption that dissolution and precipitation of zircon is much slower than that of phengite. The model was applied to zircon and phengite growth in the Nishisonogi unit of the high-P Nagasaki metamorphic complex, western Kyushu, Japan. Given that detrital zircons that are tens of microns in size remain after metamorphism, our model assumption is justified. Our results show that the duration of metamorphic zircon growth in an individual rock ranges from 10 to 20 Myr. In general, the duration of metamorphic zircon growth in the whole Nishisonogi unit is ca. 30 Myr. This prolonged duration implies that high-P metamorphism is sustained by continuous subduction of hydrated oceanic crust and overlying trench-fill sediments. The continuous subduction and accretion of these materials may supply the metamorphic fluid into the high-P metamorphic domain in the deeper part of the accretionary prism, thereby contributing to interface-controlled kinetics in the metamorphic complex., Author(s): Kazuhiro Miyazaki [sup.1], Kenshi Suga [sup.2], Yasushi Mori [sup.3], Hideki Iwano [sup.4], Koshi Yagi [sup.5], Miki Shigeno [sup.3], Tadao Nishiyama [sup.6], Tohru Danhara [sup.4], Takafumi Hirata [sup.7] Author Affiliations: [...]

Accessory mineral geochronometers such as apatite, baddeleyite, monazite, xenotime and zircon are increasingly being recognized for their ability to preserve diagnostic microstructural evidence of hypervelocity-impact processes. To date, little is known about the response of titanite to shock metamorphism, even though it is a widespread accessory phase and a U-Pb geochronometer. Here we report two new mechanical twin modes in titanite within shocked granitoid from the Chicxulub impact structure, Mexico. Titanite grains in the newly acquired core from the International Ocean Discovery Program Hole M0077A preserve multiple sets of polysynthetic twins, most commonly with composition planes (K.sub.1) = ~ [Formula omitted], and shear direction ([eta].sub.1) =, and less commonly with the mode K.sub.1 = {130}, [eta].sub.1 = ~ . In some grains, {130} deformation bands have formed concurrently with the deformation twins, indicating dislocation slip with Burgers vector b = can be active during impact metamorphism. Titanite twins in the modes described here have not been reported from endogenically deformed rocks; we, therefore, propose this newly identified twin form as a result of shock deformation. Formation conditions of the twins have not been experimentally calibrated, and are here empirically constrained by the presence of planar deformation features in quartz (12 ± 5 and ~ 17 ± 5 GPa) and the absence of shock twins in zircon (< 20 GPa). While the lower threshold of titanite twin formation remains poorly constrained, identification of these twins highlight the utility of titanite as a shock indicator over the pressure range between 12 and 17 GPa. Given the challenges to find diagnostic indicators of shock metamorphism to identify both ancient and recent impact evidence on Earth, microstructural analysis of titanite is here demonstrated to provide a new tool for recognizing impact deformation in rocks where other impact evidence may be erased, altered, or did not manifest due to generally low (< 20 GPa) shock pressure., Author(s): Nicholas E. Timms [sup.1] , Mark A. Pearce [sup.2] , Timmons M. Erickson [sup.1] [sup.3] , Aaron J. Cavosie [sup.1] , Auriol S. P. Rae [sup.4] [sup.5] , John [...]

Previous interpretations of a Jurassic subduction in Iran were based on trace element classification diagrams for granitoids, but their reliability is questionable, underscored by modern examples of continental break-up zones such as the Baja California. We present new field observations, bulk rock geochemistry, Sr and Nd isotope analyses and U-Pb zircon geochronology to assess the age and tectonic setting of previously undated intermediate to felsic magmatic rocks cropping out in the Precambrian basement of NW Iranian Azerbaijan. The geochronology revealed an uneven distribution in space and time: Late Jurassic (159-154 Ma) intrusions and dikes are alkaline to calc-alkaline. Their melt source is mantle dominated with a distinct continental contribution disclosed by radiogenic isotopes and abundant inherited zircon cores. Mid-Cretaceous (112-96 Ma) plutonic bodies and associated volcanic rocks occur only to the east of the major Siah Cheshmeh-Khoy Fault. They have geochemical signatures typical of a metasomatized mantle. In consistence with the sedimentation history of the area, our new interpretation attributes the Late Jurassic magmatism to thinning of a continental lithosphere in a rift-related setting. Mid-Cretaceous magmatism was produced by oceanic subduction beneath the Central Iran continent. We interpret the 40-Ma age gap between the two magmatic episodes as the time of opening of the oceanic basin witnessed by the Khoy ophiolite in the study area., Author(s): Anna Lechmann [sup.1] , Jean-Pierre Burg [sup.1] , Peter Ulmer [sup.1] , Ali Mohammadi [sup.1] , Marcel Guillong [sup.1] , Mohammad Faridi [sup.2] Author Affiliations: (Aff1) 0000 0001 2156 [...]

A Fe-Ti-rich garnet, clinopyroxene, and quartz eclogite sample from the 1.0 Ga Sveconorwegian orogen, SW Sweden, contains abundant quartz, rutile, and zircon in distinct micro-textural sites: garnet core, garnet rim, and matrix, constituting an ideal case for investigation of the behavior of Zr-in-rutile and Ti-in-quartz at high-pressure and temperature. A P-T path, peaking at 16.5-19 kbar and 850-900 °C, has been constrained independently for the same rock by pseudosection modelling; input pressures from this model were used for trace element geothermometry of each garnet micro-textural domain. Trace element thermo(baro)metry, based on in situ Secondary Ion Mass Spectrometry analyses of Ti contents in quartz and Zr contents in rutile, yields P-T estimates of progressive crystallization of quartz and rutile along the prograde metamorphic path. For inclusions in the garnet cores, Zr-in-rutile geothermometry yields 700-715 °C and Ti-in-quartz 620-640 °C at 7 kbar. For inclusions in the garnet rims, temperature estimates are 760-790 °C (Zr-in-rutile) and 740-920 °C (Ti-in-quartz) at 12-18 kbar. Finally, matrix rutile records 775-800 °C and locally ~ 900 °C, and quartz records temperatures up to 900 °C at 18 kbar. Ti-in-quartz estimates for the metamorphic peak (inclusions in the garnet rims and matrix) conform to the pseudosection, but appear too low for the early prograde stage (garnet cores), possibly due to lack of equilibrium at T < 700 °C. The pseudosection shows that rutile was produced by continuous ilmenite breakdown during the early stages of prograde metamorphism, a reaction that was completed at ~ 730 °C. Rutile grains in the garnet rims and the matrix grew subsequently larger by recrystallization of previously produced rutile. However, recrystallized rutile does not predominantly record peak temperatures, but instead yield 745-840 °C between 12 and 18 kbar. In the pseudosection, this temperature range broadly coincides with a stage during which (Ti-bearing) hornblende was consumed and clinopyroxene produced (i.e., dehydration); the Zr contents thus appear to reflect the last stage of efficient rutile recrystallization, catalysed by fluids released by the dehydration of hornblende preceding the metamorphic peak. Concurrently, combination of the isopleths for Ti content in quartz and Zr content in rutile (i.e. independent from pseudosection modelling) yields pressure and temperature conditions in almost perfect agreement with the P-T path as deduced from the pseudosection. The variation in Ti concentration in quartz is small regardless of crystal size, and the Ti-in-quartz geothermometer provides both precise and accurate peak temperatures of 875-920 °C, without a significant diffusional reequilibration. The lack of significant Ti diffusion in quartz is consistent with an inferred short residence time at high temperature. This study illustrates that Zr-in-rutile and Ti-in-quartz geothermobarometry can robustly constrain prograde P-T conditions and yield further insights into recrystallization processes at high temperature. The combination of these methods and integration of the results with pseudosection modelling is a versatile tool for investigating the petrologic history of high-grade rocks., Author(s): L. Tual [sup.1] [sup.2] , C. Möller [sup.1] , M. J. Whitehouse [sup.2] Author Affiliations: (Aff1) 0000 0001 0930 2361, grid.4514.4, Department of Geology, Lund University, , Sölvegatan 12, [...]

The Cretaceous Mount Daniel Complex (MDC) in northern Fiordland, New Zealand was emplaced as a 50 m-thick dyke and sheet complex into an active shear zone at the base of a Cordilleran magmatic arc. It was emplaced below the 20-25 km-thick, 125.3 ± 1.3 Ma old Western Fiordland Orthogneiss (WFO) and is characterized by metre-scale sheets of sodic, low and high Sr/Y diorites and granites. 119.3 ± 1.2 Ma old, pre-MDC lattice dykes and 117.4 ± 3.1 Ma late-MDC lattice dykes constrain the age of the MDC itself. Most dykes were isoclinally folded as they intruded, but crystallised within this deep-crustal, magma-transfer zone as the terrain cooled and was buried from 25 to 50 km (9-14 kbar), based on published P-T estimated from the surrounding country rocks. Zircon grains formed under these magmatic/granulite facies metamorphic conditions were initially characterized by conservatively assigning zircons with oscillatory zoning as igneous and featureless rims as metamorphic, representing 54% of the analysed grains. Further petrological assignment involved additional parameters such as age, morphology, Th/U ratios, REE patterns and Ti-in-zircon temperature estimates. Using this integrative approach, assignment of analysed grains to metamorphic or igneous groupings improved to 98%. A striking feature of the MDC is that only ~ 2% of all igneous zircon grains reflect emplacement, so that the zircon cargo was almost entirely inherited, even in dioritic magmas. Metamorphic zircons of MDC show a cooler temperature range of 740-640 °C, reflects the moderate ambient temperature of the lower crust during MDC emplacement. The MDC also provides a cautionary tale: in the absence of robust field and microstructural relations, the igneous-zoned zircon population at 122.1 ± 1.3 Ma, derived mostly from inherited zircons of the WFO, would be meaningless in terms of actual magmatic emplacement age of MDC, where the latter is further obscured by younger (ca. 114 Ma) metamorphic overgrowths. Thus, our integrative approach provides the opportunity to discriminate between igneous and metamorphic zircon within deep-crustal complexes. Also, without the tight field relations at Mt Daniel, the scatter beyond a statistically coherent group might be ascribed to the presence of 'antecrysts', but it is clear that the WFO solidified before the MDC was emplaced, and these older 'igneous' grains are inherited. The bimodal age range of inherited igneous grains, dominated by ~ 125 Ma and 350-320 Ma age clusters, indicate that the adjacent WFO and a Carboniferous metaigneous basement were the main sources of the MDC magmas. Mafic lenses, stretched and highly attenuated into wisps within the MDC and dominated by ~ 124 Ma inherited zircons, are considered to be entrained restitic material from the WFO. A comparison with lower- and upper-crustal, high Sr/Y metaluminous granites elsewhere in Fiordland shows that zircon inheritance is common in the deep crust, near the source region, but generally much less so in coeval, shallow magma chambers (plutons). This is consistent with previous modelling on rapid zircon dissolution rates and high Zr saturation concentrations in metaluminous magmas. Accordingly, unless unusual circumstances exist, such as MDC preservation in the deep crust, low temperatures of magma generation, or rapid emplacement and crystallization at higher structural levels, information on zircon inheritance in upper crustal, Cordilleran plutons is lost during zircon dissolution, along with information on the age, nature and variety of the source material. The observation that dioritic magmas can form at these low temperatures (< 750 °C) also suggests that the petrogenesis of mafic rocks in the arc root might need to be re-assessed., Author(s): Shrema Bhattacharya [sup.1] [sup.2] , A. I. S. Kemp [sup.1] [sup.3] , W. J. Collins [sup.4] Author Affiliations: (Aff1) 0000 0004 0474 1797, grid.1011.1, James Cook University, Geoscience, College [...]

We present new high-precision CA-ID-TIMS and in situ U-Pb ages together with Hf and O isotopic analyses (analyses performed all on the same grains) from four tuffs from the 15-10 Ma Bruneau-Jarbidge center of the Snake River Plain and from three rhyolitic units from the Kimberly borehole in the neighboring 10-6 Ma Twin Falls volcanic center. We find significant intrasample diversity in zircon ages (ranges of up to 3 Myr) and in [delta].sup.18O (ranges of up to 6â°) and [epsilon].sub.Hf (ranges of up to 24 [epsilon] units) values. Zircon rims are also more homogeneous than the associated cores, and we show that zircon rim growth occurs faster than the resolution of in situ dating techniques. CA-ID-TIMS dating of a subset of zircon grains from the Twin Falls samples reveals complex crystallization histories spanning 10.sup.4-10.sup.6 years prior to some eruptions, suggesting that magma genesis was characterized by the cyclic remelting of buried volcanic rocks and intrusions associated with previous magmatic episodes. Age-dependent trends in zircon isotopic compositions show that rhyolite production in the Yellowstone hotspot track is driven by the mixing of mantle-derived melts (normal [delta].sup.18O and [epsilon].sub.Hf) and a combination of Precambrian basement rock (normal [delta].sup.18O and [epsilon].sub.Hf down to - 60) and shallow Mesozoic and Cenozoic age rocks, some of which are hydrothermally altered (to low [delta].sup.18O values) by earlier stages of Snake River Plain magmatism. These crustal melts hybridize with juvenile basalts and rhyolites to produce the erupted rhyolites. We also observe that the Precambrian basement rock is only an important component in the erupted magmas in the first eruption at each caldera center, suggesting that the accumulation of new intrusions quickly builds an upper crustal intrusive body which is isolated from the Precambrian basement and evolves towards more isotopically juvenile and lower-[delta].sup.18O compositions over time., Author(s): Dylan P. Colón [sup.1] , Ilya N. Bindeman [sup.1] , Jörn-Frederik Wotzlaw [sup.2] , Eric H. Christiansen [sup.3] , Richard A. Stern [sup.4] Author Affiliations: (Aff1) 0000 0004 1936 [...]

Isotopic analyses of ancient mantle-derived magmatic rocks are used to trace the geochemical evolution of the Earth's mantle, but it is often difficult to determine their primary, initial isotope ratios due to the detrimental effects of metamorphism and secondary alteration. We present in situ analyses by LA-MC-ICPMS for the Pb isotopic compositions of igneous plagioclase ([An.sub.75-89]) megacrysts and the Hf isotopic compositions of BSE-imaged domains of zircon grains from two mantle-derived anorthosite complexes from south West Greenland, Fiskenaesset and Nunataarsuk, which represent two of the best-preserved Archean anorthosites in the world. In situ LA-ICPMS U-Pb geochronology of the zircon grains suggests that the minimum crystallization age of the Fiskenaesset complex is 2,936 ± 13 Ma (2σ, MSWD = 1.5) and the Nunataarsuk complex is 2,914 ± 6.9 Ma (2σ, MSWD = 2.0). Initial Hf isotopic compositions of zircon grains from both anorthosite complexes fall between depleted mantle and a less radiogenic crustal source with a total range up to 5 [ζ.sub.Hf] units. In terms of Pb isotopic compositions of plagioclase, both anorthosite complexes share a depleted mantle end member yet their Pb isotopic compositions diverge in opposite directions from this point: Fiskenaesset toward a high-μ, more radiogenic Pb, crustal composition and Nunataarsuk toward low-μ, less radiogenic Pb, crustal composition. By using Hf isotopes in zircon in conjunction with Pb isotopes in plagioclase, we are able to constrain both the timing of mantle extraction of the crustal end member and its composition. At Fiskenaesset, the depleted mantle melt interacted with an Eoarchean (~3,700 Ma) mafic crust with a maximum [sup.176]Lu/[sup.177]Hf ~0.028. At Nunataarsuk, the depleted mantle melt interacted with a Hadean (~4,200 Ma) mafic crust with a maximum [sup.176]Lu/[sup.177]Hf ~0.0315. Evidence from both anorthosite complexes provides support for the long-term survival of ancient mafic crusts that, although unidentified at the surface to date, could still be present within the Fiskenasset and Nunataarsuk regions. Keywords Archean * Anorthosites * LA-MC-ICPMS * Pb-Pb isotopes * Lu-Hf isotopes, Introduction Long-lived radiogenic isotope systems (e.g. Sm-Nd, Lu-Hf, Pb-Pb) are powerful tracers of geochemical processes. They have been used extensively to track complementary processes such as the geochemical depletion of [...]

The sorption and complexation of zirconium with Arsenazo III have been studied on a polyacrylonitrile fibrous material filled with strongly acidic KU-2 cation exchanger in strongly acidic media. The optimal conditions have been chosen for the sorption--spectrophotometric and test determination of zirconium by diffuse reflection spectroscopy or visual testing. The limit of zirconium detection is 0.02 µg/mL. The procedure was tested in the analysis of model solutions of ammonium molybdate and vanadate and copper chloride using the standard addition method. Keywords: diffuse reflection spectroscopy, zirconium, fibrous KU-2 cation exchanger, Arsenazo III. DOI: 10.1134/S1061934812060172, The reagents proposed for the photometric determination of zirconium include Xylenol Orange, Pyrocatechol Violet, Phenylfluorone, Alizarin sulfonate, and others [1-4]. Bisazosubstituted compounds of chromotropic acid--sulfochlorophenol C and analogues of Arsenazo [...]

A sensitive and simple method for the electrothermal atomic absorption spectrometry (ETAAS) determination of Cr(III) after separation/preconcentration on a micro-column packed with nanometer sized zirconium phosphate has been developed. Total chromium was determined after the reduction of Cr(VI) to Cr(III) by 10% (m/v) of aqueous ascorbic acid. The limit of detection for Cr(III) was 1.5 ng/L with an enrichment factor of 300. The static adsorption capacity of the sorbent for Cr(III) was 9.34 mg/g. The relative standard deviation was 3.2% (n = 7, c = 10 ng/mL). The method was applied successfully to the determination of Cr(III) and Cr(VI) in natural water samples. Keywords: chromium, speciation, nanometer zirconium phosphate, ETAAS, water. DOI: 10.1134/S1061934812050140, Chromium is one of environmental pollutants due to its wide use in various industrial processes, including steel works, electroplating, tanning, chemical industries, oxidative dyeing, and cooling water towers [1, 2]. [...]

Byline: D. J. Cherniak (1), E. B. Watson (1) Keywords: Lithium; Zircon; Diffusion; Nuclear reaction analysis Abstract: Diffusion of Li under anhydrous conditions at 1 atm and under fluid-present elevated pressure (1.0--1.2 GPa) conditions has been measured in natural zircon. The source of diffusant for 1-atm experiments was ground natural spodumene, which was sealed under vacuum in silica glass capsules with polished slabs of zircon. An experiment using a Dy-bearing source was also conducted to evaluate possible rate-limiting effects on Li diffusion of slow-diffusing REE.sup.+3 that might provide charge balance. Diffusion experiments performed in the presence of [H.sub.2]O--CO.sub.2 fluid were run in a piston--cylinder apparatus, using a source consisting of a powdered mixture of spodumene, quartz and zircon with oxalic acid added to produce [H.sub.2]O--CO.sub.2 fluid. Nuclear reaction analysis (NRA) with the resonant nuclear reaction 7.sup.Li(p,I[3).sup.8]Be was used to measure diffusion profiles for the experiments. The following Arrhenius parameters were obtained for Li diffusion normal to the c-axis over the temperature range 703--1.151degC at 1 atm for experiments run with the spodumene source: D.sub.Li = 7.17 10.sup. - 7 ( - 275 [+ or -] 11 kJmol.sup. - 1 /RT)m.sup.2 s.sup. - 1. Diffusivities are similar for transport parallel to the c-axis, indicating little anisotropy for Li diffusion in zircon. Similar Li diffusivities were also found for experiments run under fluid-present conditions and for the experiment run with the Dy-bearing source. Li diffusion is considerably faster than diffusion of other cations in zircon, with a smaller activation energy for diffusion. Although Li diffusion in zircon is comparatively rapid, zircons will be moderately retentive of Li signatures at mid-crustal metamorphic temperatures, but they are unlikely to retain this information for geologically significant times under high-grade metamorphism. Author Affiliation: (1) Department of Earth and Environmental Sciences, Rensselaer Polytechnic Institute, Science Center 1W19, 110 8th St., Troy, NY, 12180, USA Article History: Registration Date: 31/12/2009 Received Date: 08/08/2009 Accepted Date: 30/12/2009 Online Date: 10/01/2010 Article note: Communicated by T. L. Grove.

Byline: Sarah K. Appleby (1,6), Martin R. Gillespie (2), Colin M. Graham (1), Richard W. Hinton (1), Grahame J. H. Oliver (3), Nigel M. Kelly (4) Keywords: S-type granites; Scottish Caledonian granites; Zircon; Oxygen isotopes; Hf isotopes; Granite sources Abstract: In contrast to I-type granites, which commonly comprise infracrustal and supracrustal sources, S-type granites typically incorporate predominantly supracrustal sources. The initial aim of this study was to identify the sources of three Scottish Caledonian (~460 Ma) S-type granites (Kemnay, Cove and Nigg Bay) by conducting oxygen, U--Pb and Hf isotope analyses in zircon in order to characterise one potential end-member magma involved in the genesis of the voluminous late Caledonian (~430--400 Ma) I-type granites. Field, whole-rock geochemical and isotopic data are consistent with the generation of the S-type granites by melting their Dalradian Supergroup country rocks. While Hf isotope compositions of magmatic zircon, U--Pb data of inherited zircons, and high mean zircon [delt[a].sup.18]O values of 9.0 +- 2.7[per thousand] (2SD) and 9.8 +- 2.0[per thousand] for the Kemnay and Cove granites support this model, the Nigg Bay Granite contains zircons with much lower [delt[a].sup.18]O values (6.8 +- 2.1[per thousand]), similar to those found in Scottish I-type granites. This suggests that the Nigg Bay Granite contains low-[delt[a].sup.18]O material representing either altered supracrustal material, or more likely, an infracrustal source component with mantle-like [delt[a].sup.18]O. Mixing trends in plots of [delt[a].sup.18]O vs. [epsilon]Hf for S-type granite zircons indicate involvement of at least two sources in all three granites. This pilot study of Scottish Caledonian S-type granites demonstrates that, while field and whole-rock geochemical data are consistent with local melting of only supracrustal sources, the oxygen isotopic record stored in zircon reveals a much more complex petrogenetic evolution involving two or more magma sources. Author Affiliation: (1) Grant Institute of Earth Science, University of Edinburgh, West Mains Road, Edinburgh, EH9 3JW, UK (2) British Geological Survey, Murchison House, West Mains Road, Edinburgh, EH9 3LA, UK (3) Crustal Geodynamics Group, School of Geography and Geosciences, University of St Andrews, St Andrews, KY16 9AL, UK (4) Department of Geology and Geological Engineering, Colorado School of Mines, 1516 Illinois Street, Golden, CO, 80401, USA (5) Edinburgh Ion Microprobe Facility, University of Edinburgh, West Mains Road, Edinburgh, EH9 3JW, UK (6) Advanced Mineralogy Research Center, Colorado School of Mines, 1310 Maple Street, Golden, CO, 80401, USA Article History: Registration Date: 18/11/2009 Received Date: 24/07/2009 Accepted Date: 16/11/2009 Online Date: 06/12/2009 Article note: Communicated by J. Hoefs. Electronic supplementary material The online version of this article (doi: 10.1007/s00410-009-0469-3) contains supplementary material, which is available to authorized users.

Byline: Marieke Lichtervelde (1), Francois Holtz (1), John M. Hanchar (2) Keywords: Manganotantalite; Zircon; Solubility; Dissolution and crystallization experiments; Competition; Pegmatite Abstract: The behavior of tantalum and zirconium in pegmatitic systems has been investigated through the determination of Ta and Zr solubilities at manganotantalite and zircon saturation from dissolution and crystallization experiments in hydrous, Li-, F-, P- and B-bearing pegmatitic melts. The pegmatitic melts are synthetic and enriched in flux elements: 0.7--1.3 wt% [Li.sub.2]O, 2--5.5 wt% F, 2.8--4 wt% [P.sub.2]O.sub.5 and 0--2.8 wt% [B.sub.2]O.sub.3, and their aluminum saturation index ranges from peralkaline to peraluminous (ASI.sub.Li = Al/[Na + K + Li] = 0.8 to 1.3) with various K/Na ratios. Dissolution and crystallization experiments were conducted at temperatures varying between 700 and 1,150degC, at 200 MPa and nearly water-saturated conditions. For dissolution experiments, pure synthetic, end member manganotantalite and zircon were used in order to avoid problems with slow solid-state kinetics, but additional experiments using natural manganotantalite and zircon of relatively pure composition (i.e., close to end member composition) displayed similar solubility results. Zircon and manganotantalite solubilities considerably increase from peraluminous to peralkaline compositions, and are more sensitive to changes in temperature or ASI of the melt than to flux content. A model relating the enthalpy of dissolution of manganotantalite to the ASI.sub.Li of the melt is proposed: aH .sub.diss (kJ/mol) = 304 x ASI.sub.Li - 176 in the peralkaline field, and aH .sub.diss (kJ/mol) = -111 x ASI.sub.Li + 245 in the peraluminous field. The solubility data reveal a small but detectable competitivity between Zr and Ta in the melt, i.e., lower amounts of Zr are incorporated in a Ta-bearing melt compared to a Ta-free melt under the same conditions. A similar behavior is observed for Hf and Ta. The competitivity between Zr (or Hf) and Ta increases from peraluminous to peralkaline compositions, and suggests that Ta is preferentially bonded to non-bridging oxygens (NBOs) with Al as first-neighbors, whereas Zr is preferentially bonded to NBOs formed by excess alkalies. As a consequence Zr/Ta ratios, when buffered by zircon and manganotantalite simultaneously, are higher in peralkaline melts than in peraluminous melts. Author Affiliation: (1) Institut fur Mineralogie, Leibniz Universitat Hannover, Callinstr. 3, 30167, Hannover, Germany (2) Department of Earth Sciences, Memorial University of Newfoundland, 300 Prince Philip Drive, St. John's, NL, A1B 3X5, Canada Article History: Registration Date: 26/10/2009 Received Date: 07/05/2009 Accepted Date: 26/10/2009 Online Date: 12/11/2009 Article note: Communicated by H. Keppler.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.earscirev.2009.10.011 Byline: Harald G. Dill Keywords: economic geology; mineral deposits; geology; mineralogy; classification scheme; spreadsheet Abstract: Economic geology is a mixtum compositum of all geoscientific disciplines focused on one goal, finding new mineral depsosits and enhancing their exploitation. The keystones of this mixtum compositum are geology and mineralogy whose studies are centered around the emplacement of the ore body and the development of its minerals and rocks. In the present study, mineralogy and geology act as x- and y-coordinates of a classification chart of mineral resources called the 'chessboard' (or 'spreadsheet') classification scheme. Magmatic and sedimentary lithologies together with tectonic structures (1-D/pipes, 2-D/veins) are plotted along the x-axis in the header of the spreadsheet diagram representing the columns in this chart diagram. 63 commodity groups, encompassing minerals and elements are plotted along the y -axis, forming the lines of the spreadsheet. These commodities are subjected to a tripartite subdivision into ore minerals, industrial minerals/rocks and gemstones/ornamental stones. Further information on the various types of mineral deposits, as to the major ore and gangue minerals, the current models and the mode of formation or when and in which geodynamic setting these deposits mainly formed throughout the geological past may be obtained from the text by simply using the code of each deposit in the chart. This code can be created by combining the commodity (lines) shown by numbers plus lower caps with the host rocks or structure (columns) given by capital letters. Each commodity has a small preface on the mineralogy and chemistry and ends up with an outlook into its final use and the supply situation of the raw material on a global basis, which may be updated by the user through a direct link to databases available on the internet. In this case the study has been linked to the commodity database of the US Geological Survey. The internal subdivision of each commodity section corresponds to the common host rock lithologies (magmatic, sedimentary, and metamorphic) and structures. Cross sections and images illustrate the common ore types of each commodity. Ore takes priority over the mineral. The minerals and host rocks are listed by their chemical and mineralogical compositions, respectively, separated from the text but supplemented with cross-references to the columns and lines, where they prevalently occur. A metallogenetic-geodynamic overview is given at the bottom of each column in the spreadsheet. It may be taken as the 'sum' or the ' mean' of a number of geodynamic models and ideas put forward by the various researchers for all the deposits pertaining to a certain clan of lithology or structure. This classical or conservative view of metallotects related to the common plate tectonic settings is supplemented by an approach taken for the first time for such a number of deposits, using the concepts of sequence stratigraphy. This paper, so as to say, is a 'launch pad' for a new mindset in metallogenesis rather than the final result. The relationship supergene-hypogene and syngenetic-epigenetic has been the topic of many studies for ages but to keep them as separate entities is often unworkable in practice, especially in the so-called epithermal or near-surface/shallow deposits. Vein-type and stratiform ore bodies are generally handled also very differently. To get these different structural elements (space) and various mineralizing processes (time) together and to allow for a forward modeling in mineral exploration, architectural elements of sequence stratigraphy are adapted to mineral resources. Deposits are geological bodies which need accommodation space created by the environment of formation and the tectonic/geodynamic setting through time. They are controlled by horizontal to subhorizontal reference planes and/or vertical structures. Prerequisites for the deposits to evolve are thermal and/or mechanical gradients. Thermal energy is for most of the settings under consideration deeply rooted in the mantle. A perspective on how this concept might work is given in the text by a pilot project on mineral deposits in Central Europe and in the spreadsheet classification scheme by providing a color-coded categorization into 1. mineralization mainly related to planar architectural elements, e.g. sequence boundaries subaerial and unconformities 2. mineralization mainly related to planar architectural elements, e.g. sequence boundaries submarine, transgressive surfaces and maximum flooding zones/surfaces) 3. mineralization mainly controlled by system tracts (lowstand system tracts transgressive system tracts, highstand system tracts) 4. mineralization of subvolcanic or intermediate level to be correlated with the architectural elements of basin evolution 5. mineralization of deep level to be correlated with the deep-seated structural elements. There are several squares on the chessboard left blank mainly for lack of information on sequence stratigraphy of mineral deposits. This method has not found many users yet in mineral exploration. This review is designed as an 'interactive paper' open, for amendments in the electronic spreadsheet version and adjustable to the needs and wants of application, research and training in geosciences. Metamorphic host rock lithologies and commodities are addressed by different color codes in the chessboard classification scheme. Article History: Received 6 July 2008; Accepted 23 October 2009

Byline: Craig B. Grimes (1,4), Barbara E. John (1), Michael J. Cheadle (1), Frank K. Mazdab (2), Joseph L. Wooden (2), Susan Swapp (1), Joshua J. Schwartz (3) Abstract: We characterize the textural and geochemical features of ocean crustal zircon recovered from plagiogranite, evolved gabbro, and metamorphosed ultramafic host-rocks collected along present-day slow and ultraslow spreading mid-ocean ridges (MORs). The geochemistry of 267 zircon grains was measured by sensitive high-resolution ion microprobe-reverse geometry at the USGS-Stanford Ion Microprobe facility. Three types of zircon are recognized based on texture and geochemistry. Most ocean crustal zircons resemble young magmatic zircon from other crustal settings, occurring as pristine, colorless euhedral (Type 1) or subhedral to anhedral (Type 2) grains. In these grains, Hf and most trace elements vary systematically with Ti, typically becoming enriched with falling Ti-in-zircon temperature. Ti-in-zircon temperatures range from 1,040 to 660degC (corrected for a .sub.TiO2 [approximately equal to] 0.7, a .sub.SiO2 [approximately equal to] 1.0, pressure [approximately equal to] 2 kbar) intra-sample variation is typically ~60--150degC. Decreasing Ti correlates with enrichment in Hf to ~2 wt%, while additional Hf-enrichment occurs at relatively constant temperature. Trends between Ti and U, Y, REE, and Eu/Eu* exhibit a similar inflection, which may denote the onset of eutectic crystallization the inflection is well-defined by zircons from plagiogranite and implies solidus temperatures of ~680--740degC. A third type of zircon is defined as being porous and colored with chaotic CL zoning, and occurs in ~25% of rock samples studied. These features, along with high measured La, Cl, S, Ca, and Fe, and low (Sm/La).sub.N ratios are suggestive of interaction with aqueous fluids. Non-porous, luminescent CL overgrowth rims on porous grains record uniform temperatures averaging 615 +- 26degC (2SD, n = 7), implying zircon formation below the wet-granite solidus and under water-saturated conditions. Zircon geochemistry reflects, in part, source region elevated HREE coupled with low U concentrations allow effective discrimination of ~80% of zircon formed at modern MORs from zircon in continental crust. The geochemistry and textural observations reported here serve as an important database for comparison with detrital, xenocrystic, and metamorphosed mafic rock-hosted zircon populations to evaluate provenance. Author Affiliation: (1) Department of Geology and Geophysics, University of Wyoming, Laramie, WY, 82071, USA (2) U.S.G.S.-Stanford Ion Microprobe Laboratory, 367 Panama Mall, Stanford, CA, 94305, USA (3) Department of Geological Sciences, University of Alabama, 870338, Tuscaloosa, AL, 35487, USA (4) Department of Geology and Geophysics, University of Wisconsin, 1215 West Dayton Street, Madison, WI, 53706, USA Article History: Registration Date: 24/04/2009 Received Date: 17/11/2008 Accepted Date: 24/04/2009 Online Date: 19/05/2009 Article note: Communicated by H. Keppler. Electronic supplementary material The online version of this article (doi: 10.1007/s00410-009-0409-2) contains supplementary material, which is available to authorized users.

Byline: Arnaud Villaros (1), Gary Stevens (1), Jean-Francois Moyen (1), Ian S. Buick (1) Keywords: S-type granite; Trace element; Partial melting; Geochemical modelling; Accessory phases; Cape Granite Suite Abstract: Within individual plutons, the trace element concentrations in S-type granites generally increase with maficity (total iron and magnesium content and expressed as atomic Fe + Mg in this study) the degree of variability in trace element concentration also expands markedly with the same parameter. The strongly peraluminous, high-level S-type granites of the Peninsular Pluton (Cape Granite Suite, South Africa) are the product of biotite incongruent melting of a metasedimentary source near the base of the crust. Leucogranites within the suite represent close to pure melts from the anatectic source and more mafic varieties represent mixtures of melt and peritectic garnet and ilmenite. Trace elements such as Rb, Ba, Sr and Eu, that are concentrated in reactant minerals in the melting process, show considerable scatter within the granites. This is interpreted to reflect compositional variation in the source. In contrast, elements such as LREE, Zr and Hf, which are concentrated within refractory accessory phases (zircon and monazite), show well-defined negative correlations with increasing SiO.sub.2 and increase linearly with increasing maficity. This is interpreted to reflect coupled co-entrainment of accessory minerals and peritectic phases to the melt: leucocratic rocks cannot have evolved from the more mafic compositions in the suite by a process of fractional crystallisation because in this case they would have inherited the zircon-saturated character of this hypothetical earlier magma. Trace element behaviour of granites from the Peninsular Pluton has been modelled via both equilibrium and disequilibrium trace element melting. In the disequilibrium case, melts are modelled as leaving the source with variable proportions of entrained peritectic phases and accessory minerals, but before the melt has dissolved any accessory minerals. Thus, the trace element signature of the melt is largely inherited from the reactants in the melting reaction, with no contribution from zircon and monazite dissolution. In the equilibrium case, melt leaves the source with entrained crystals, after reaching zircon and monazite saturation. A significant proportion of the rocks of the Peninsular Pluton have trace element concentrations below those predicted by zircon and monazite saturation. In the case of the most leucocratic rocks all compositions are zircon undersaturated whilst the majority of the most mafic compositions are zircon oversaturated. However, in both cases, zircon is commonly xenocrystic. Thus, the leucocratic rocks represent close to pure melts, which escaped their sources rapidly enough that some very closely match the trace element disequilibrium melting model applied in this study. Zircon dissolution rates allow the residency time for the melt in the source to be conservatively estimated at less than 500 years. Author Affiliation: (1) Department of Geology, Geography and Environmental Studies, Centre for Crustal Petrology, Stellenbosch University, Private Bag X1, Matieland, South Africa Article History: Registration Date: 25/02/2009 Received Date: 06/10/2008 Accepted Date: 25/02/2009 Online Date: 24/03/2009 Article note: Communicated by T. L. Grove. Electronic supplementary material The online version of this article (doi: 10.1007/s00410-009-0396-3) contains supplementary material, which is available to authorized users.

Byline: JiAi Zak (1,2), Scott R. Paterson (3), VojtAch Janousek (2,4), Petr Kabele (5) Keywords: Emplacement; Granite; Incremental growth; Magma chamber; Pluton; Thermal--mechanical modeling Abstract: The Mammoth Peak sheeted intrusive complex formed in the interior of a ~7--10 km deep magma chamber, specifically in the Half Dome granodiorite of the Tuolumne batholith, central Sierra Nevada, CA (USA). The sheets consist of fractionated melts with accumulated hornblende, biotite, magnetite, titanite, apatite, and zircon. The accumulation, especially of titanite, had a profound effect on minor and trace elements (Nb, Ta, Ti, REE, U, Th, P, Zr, Hf, etc.), increasing their contents up to five to six times. Our thermal--mechanical modeling using the finite element method shows that cooling-generated tensile stresses resulted in the inward propagation of two perpendicular sets of dilational cracks in the host granodiorite. We interpret the sheeted complex to have formed by a crack-seal mechanism in a high strength, crystal-rich mush, whereby outward younging pulses of fractionated magma were injected into these syn-magmatic cracks at the margin of an active magma chamber. Thermal--mechanical instabilities developed after the assembly of the sheeted complex, which was then overprinted by late ~NW--SE magmatic foliation. This case example provides a cautionary note regarding the interpretation that sheeted zones in large granitoid plutons imply a diking mechanism of growth because the sheeted/dike complexes in plutons (1) may display inverse growth directions from the growth of the overall intrusive sequence (2) need not record initial chamber construction and instead may reflect late pulsing of magma within an already constructed magma chamber (3) have an overprinting magmatic fabric indicating the continued presence of melt after construction of sheeted complexes and thus a prolonged thermal history as compared to dikes and (4) because the scale of the observed sheeted complexes may be small ( Author Affiliation: (1) Institute of Geology and Paleontology, Faculty of Science, Charles University, Albertov 6, 12843, Prague, Czech Republic (2) Czech Geological Survey, Klarov 3, 11821, Prague, Czech Republic (3) Department of Earth Sciences, University of Southern California, 3651 Trousdale Parkway, Los Angeles, CA, 90089-0740, USA (4) Institute of Petrology and Structural Geology, Faculty of Science, Charles University, Albertov 6, 12843, Prague, Czech Republic (5) Department of Mechanics, Faculty of Civil Engineering, Czech Technical University in Prague, Thakurova 7, 16629, Prague, Czech Republic Article History: Registration Date: 17/02/2009 Received Date: 22/07/2008 Accepted Date: 17/02/2009 Online Date: 13/03/2009 Article note: Communicated by T.L. Grove. Electronic supplementary material The online version of this article (doi: 10.1007/s00410-009-0391-8) contains supplementary material, which is available to authorized users.

Byline: Birger Rasmussen (1), Andreas G. Mueller (2), Ian R. Fletcher (1) Keywords: Zirconolite; Xenotime; U--Pb dating; SHRIMP; Gold mineralization; Yilgarn craton Abstract: In situ SHRIMP U--Pb dating of magmatic zirconolite ([CaZrTi.sub.2]O.sub.7) in the Golden Mile Dolerite from the Mt Charlotte gold deposit (Yilgarn Craton, Australia) has yielded the first robust emplacement age (2,680 +- 9 Ma) for the principle host-rock of gold mineralization in the Kalgoorlie district. In contrast, co-magmatic zircon gave ages from ~2.68 Ga to ~2.17 Ga, reflecting isotopic resetting of high-U and -Th crystals. In situ SHRIMP analysis of hydrothermal xenotime (YPO.sub.4), which co-exists with gold in alteration pyrite, provided a Pb/Pb isochron age of 2,655 +- 13 Ma. This date indicates that the youngest deposit in the Kalgoorlie district (Mt Charlotte) formed at ~2.65 Ga, and provides a new minimum age for the structurally older Golden Mile deposit. Our results indicate that gold mineralization at Mt Charlotte is ~50 million years older than indicated by recent 40.sup.Ar/ [.sup.39]Ar dating and places new constraints on the timing of late-stage regional faulting (D.sub.4) in the province. Author Affiliation: (1) Department of Applied Geology, Curtin University of Technology, GPO Box U1987, Perth, WA, 6845, Australia (2) 12a Belgrave Street, Maylands, WA, 6051, Australia Article History: Registration Date: 06/10/2008 Received Date: 13/05/2008 Accepted Date: 06/10/2008 Online Date: 06/11/2008 Article note: Communicated by T.L. Grove.

Byline: Steven Michael Reddy (1), Nicholas E. Timms (1), Patrick Joseph Hamilton (1,3), Helen R. Smyth (2) Keywords: Arc magmatism; Cumulate; Electron backscatter diffraction (EBSD); Cathodoluminescence; Crystal plasticity; Dislocation creep Abstract: An undeformed glomeroporphyritic andesite from the Sunda Arc of Java, Indonesia, contains zoned plagioclase and amphibole glomerocrysts in a fine-grained groundmass and records a complex history of adcumulate formation and subsequent magmatic disaggregation. A suite of xenocrystic zircon records Proterozoic and Archaean dates whilst a discrete population of zoned, euhedral, igneous zircon yields a SHRIMP U-Pb crystallisation age of 9.3 +- 0.2 Ma. Quantitative microstructural analysis of zircon by electron backscatter diffraction (EBSD) shows no deformation in the inherited xenocrysts, but intragrain orientation variations of up to 30deg in 80% of the young zircon population. These variations are typically accommodated by both progressive crystallographic bending and discrete low angle boundaries that overprint compositional growth zoning. Dispersion of crystallographic orientations are dominantly by rotation about an axis parallel to the zircon c-axis [001], which is coincident with the dominant orientation of misorientation axes of adjacent analysis points in EBSD maps. Less common misorientation axes account for minor components of crystallographic dispersion. These observations are consistent with zircon deformation by dislocation creep and the formation of tilt and twist boundaries associated with the operation of {100} and {010} slip systems. The restriction of deformation microstructures to large glomerocrysts and the young magmatic zircon population, and the absence of deformation within the host igneous rock and inherited zircon grains, indicate that zircon deformation took place within a low-melt fraction ( Author Affiliation: (1) Department of Applied Geology, The Institute for Geoscience Research, Curtin University of Technology, GPO Box U1987, Perth, WA, 6845, Australia (2) Department of Earth Sciences, CASP, University of Cambridge, Cambridge, CB3 0DH, UK (3) Intellection Pty. Ltd, 27 Mayneview Street, Milton, QL, 4064, Australia Article History: Registration Date: 18/07/2008 Received Date: 15/10/2007 Accepted Date: 18/07/2008 Online Date: 05/08/2008 Article note: Communicated by B. Collins.