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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 [...]

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 [...]

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 [...]

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 [...]

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: [...]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.earscirev.2005.11.001 Byline: J.J. Veevers (a), E.A. Belousova (a), A. Saeed (a), K. Sircombe (b), A.F. Cooper (c), S.E. Read (c) Keywords: Australia; Antarctica; detrital zircons; 700-500 Ma; Pan-Gondwanaland; Hf-isotopes; trace elements; T .sub.DM; paleogeography; alkaline provenance Abstract: Eastern Australian sediments of Cambrian, Ordovician, Silurian-Devonian, Triassic, and Neogene ages are known to be dominated by zircons dated 700-500 Ma ('Southwest Pacific-Gondwana igneous component') by the U-Pb SHRIMP method, and thought to be derived from Antarctica, as suggested also by paleogeographical evidence. To extend the characteristics of the provenance we subjected SHRIMPed zircons from the Middle Triassic Hawkesbury Sandstone and four Neogene beach sands to LAM-ICPMS analysis for rock type and Hf-isotope T .sub.DM model ages. These data confirm the demonstration (from ages alone) that the beach sands were recycled from the Hawkesbury Sandstone. All five samples have a substantial fraction of 700-500 Ma zircons derived from alkaline rocks with T .sub.DM of 2.0-1.0 Ga. We analysed zircons from the nearest exposed alkaline rock of appropriate age in Antarctica: the 550-500 Ma Koettlitz Glacier Alkaline Province of the Ross orogen of the Transantarctic Mountains, emplaced during contemporary transtension. The rock types and T .sub.DM of the Koettlitz Glacier Alkaline Province zircons match those of the eastern Australian samples but only over the restricted range of 550-500 Ma. Rocks of 700-550 Ma age and alkaline type are unknown in Antarctic exposures. Rocks of this age and type, however, abound in the Pan-Gondwanaland orogens. The nearest of these is the Leeuwin Complex of the Pinjarra orogen of southwestern Australia, which connects through the Prydz-Leeuwin Belt with the Mozambique Orogenic Belt. In turn, the Leeuwin Complex is dominated by 700-500 Ma alkaline rocks generated by contemporary transtension. We find that zircons from a beach sand at Eneabba, 450 km north of the Leeuwin Complex, are dominated by alkaline types, so confirming demonstration by age alone that the sand came from the Leeuwin Complex. An important inference is that Pan-Gondwanaland terranes are potential provenances of sediment with zircons of ages 700-500 Ma, model ages 2.0-1.0 Ga, and alkaline affinity. We compiled the age spectra of our samples with others of the Southwest Pacific-Gondwana igneous component in southern Australia and reviewed their paleogeographical data. The Early Cambrian turbidites of the Kanmantoo Group were deposited from an axial northward paleocurrent that flowed across adjacent Antarctica in Wilkes Land. The Ordovician turbidite was deposited in fore-arc and abyssal fans likewise from a northward paleocurrent that flowed parallel to the uplifted Ross-Delamerian orogen. The Ordovician-Silurian-Devonian Mathinna Supergroup was deposited in a submarine fan system that prograded to the east-northeast from high ground in Antarctica. The Hawkesbury Sandstone was deposited in a braided-river system on a surface that sloped to the north-northeast from high ground in Antarctica. Together with the zircon data, the paleogeographical evidence in the Cambrian, Ordovician, Ordovician-Silurian-Devonian, and Triassic all point to a provenance in Wilkes Land, Antarctica of Pan-Gondwanaland (700-500 Ma) terranes with alkaline rocks. Author Affiliation: (a) GEMOC ARC National Key Centre, Department of Earth and Planetary Sciences, Macquarie University, Sydney NSW 2109, Australia (b) TSRC, School of Earth and Geographical Sciences, University of Western Australia, Crawley WA 6009, Australia (c) Geology Department, University of Otago, PO Box 56, Dunedin, New Zealand Article History: Received 19 April 2005; Accepted 16 November 2005 Article Note: (footnote) [star] Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.earscirev.2005.11.001.

Byline: J. W. Valley (1), J. S. Lackey (9,1), A. J. Cavosie (10,1), C. C. Clechenko (1), M. J. Spicuzza (1), M. A. S. Basei (2), I. N. Bindeman (3), V. P. Ferreira (4), A. N. Sial (4), E. M. King (5), W. H. Peck (6), A. K. Sinha (7), C. S. Wei (8) Abstract: Analysis of [delt[a].sup.18]O in igneous zircons of known age traces the evolution of intracrustal recycling and crust-mantle interaction through time. This record is especially sensitive because oxygen isotope ratios of igneous rocks are strongly affected by incorporation of supracrustal materials into melts, which commonly have [delt[a].sup.18]O values higher than in primitive mantle magmas. This study summarizes data for [delt[a].sup.18]O in zircons that have been analyzed from 1,200 dated rocks ranging over 96% of the age of Earth. Uniformly primitive to mildly evolved magmatic [delt[a].sup.18]O values are found from the first half of Earth history, but much more varied values are seen for younger magmas. The similarity of values throughout the Archean, and comparison to the composition of the 'modern' mantle indicate that [delt[a].sup.18]O of primitive mantle melts have remained constant (+-0.2[per thousand]) for the past 4.4 billion years. The range and variability of [delt[a].sup.18]O in all Archean zircon samples is subdued ([delt[a].sup.18]O(Zrc)=5--7.5[per thousand]) ranging from values in high temperature equilibrium with the mantle (5.3+- 0.3[per thousand]) to slightly higher, more evolved compositions (6.5--7.5[per thousand]) including samples from: the Jack Hills (4.4--3.3 Ga), the Beartooth Mountains (4.0--2.9 Ga), Barberton (3.5--2.7 Ga), the Superior and Slave Provinces (3.0 to 2.7 Ga), and the Lewisian (2.7 Ga). No zircons from the Archean have been analyzed with magmatic [delt[a].sup.18]O above 7.5[per thousand]. The mildly evolved, higher Archean values (6.5--7.5[per thousand]) are interpreted to result from exchange of protoliths with surface waters at low temperature followed by melting or contamination to create mildly elevated magmas that host the zircons. During the Proterozoic, the range of [delt[a].sup.18]O(Zrc) and the highest values gradually increased in a secular change that documents maturation of the crust. After [proportional to]1.5 Ga, high [delt[a].sup.18]O zircons (8 to >10[per thousand]) became common in many Proterozoic and Phanerozoic terranes reflecting [delt[a].sup.18]O(whole rock) values from 9 to over 12[per thousand]. The appearance of high [delt[a].sup.18]O magmas on Earth reflects nonuniformitarian changes in the composition of sediments, and rate and style of recycling of surface-derived material into magmas within the crust. Author Affiliation: (1) Department of Geology, University of Wisconsin, Madison, WI, 53706, USA (2) Department de Mineralogia Geotectonica, University Sao Paulo, Sao Paulo, Brazil (3) Department of Geological Sciences, University of Oregon, Eugene, OR, 97403, USA (4) NEG-LABISE, Department of Geology, Federal University of Pernambuco, Recife, PE, 50670-000, Brazil (5) Department of Geography and Geology, Illinois State University, Normal, IL, 61790, USA (6) Department of Geology, Colgate University, Hamilton, NY, 13346, USA (7) Virginia Polytechnic Inst., Blacksburg, VA, USA (8) School of Earth and Space Sciences, University of Science and Technology of China, Hefei, Anhui, 230026, China (9) Department of Geology, College of Wooster, Wooster, OH, 44691, USA (10) Department of Geology, University of Puerto Rico, Mayaguez, PR, 00681-9017, USA Article History: Registration Date: 04/08/2005 Received Date: 07/04/2005 Accepted Date: 11/07/2005 Online Date: 09/11/2005 Article note: Electronic Supplementary Material Supplementary material is available for this article at http://dx.doi.org/10.1007/s00410-005-0025-8 Communicated by J. Hoefs

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.earscirev.2004.05.005 Byline: J.J. Veevers, A. Saeed, E.A. Belousova, W.L. Griffin Keywords: Australia; Yilgarn Craton; Perth Basin; U-Pb ages; Hf-isotopes; Permian sandstone; Modern sand; Source composition; Detrital zircons; Paleogeographical and denudational history Abstract: Detrital zircons from the Permian Collie Coal Measures and modern sands on the northern part of the Albany Province have been analysed for U-Pb ages by a laser ablation microprobe-inductively coupled plasma mass spectrometer (LAM-ICPMS) and for Hf-isotope compositions by a laser ablation microprobe multi-collector inductively coupled plasma mass spectrometer (LAM-MC-ICPMS). Trace elements were determined by analysis on the electron microprobe (EMP) and the ICPMS's. This combination of techniques makes it possible to determine for each grain not only the age but the nature and source of the host magma, whether crustal or juvenile mantle, and a model age (T.sub.DM) based on a depleted-mantle source, which gives a minimum age for the source material of the magma from which the zircon crystallised. The integrated analysis, applied to suites of detrital zircon, gives a more distinctive, and more easily interpreted, picture of crustal evolution in the provenance area than age data alone. Zircons from Permian and Triassic sediments already analysed for U-Pb ages by a sensitive high-resolution ion microprobe (SHRIMP) were also analysed for Hf isotopes and trace elements. Zircons from Collie and Permian and Early Triassic rocks of the northern Perth Basin have an age spectrum with a peak at about 1200 Ma that can be traced to the Albany Province. Differences, however, in Hf-isotope composition indicate that the Collie Coal Measures and the northern Perth Basin sandstones were not derived from the northern part of the Albany Province or from the coastal strip of felsic granitoids. The Perth Basin samples have a second peak age of 600-500 Ma that can be traced to the Leeuwin Block. One of the modern sands has a major peak at 2616 Ma that can be traced to the Yilgarn Craton. Compiled with previously published U-Pb zircon age spectra, the analyses provide insights into the paleogeographical history. The Yilgarn Craton sloped from the north at 1700 Ma, from the southeast at 1350-1140 and 490 Ma, its eastern part to the east at 300 Ma, and the southern part to the northwest from the Albany Province at 300-255 Ma. Denudational data from apatite fission-track analysis and vitrinite-reflectance studies suggest that the Yilgarn Craton was covered by a [approximately equal to]5-km-thick blanket of Permian and Mesozoic sedimentary rock that was almost entirely removed by the Cenozoic, possibly because the craton was situated between the shoulders of rift systems that grew into the eastern and southeastern Indian Ocean. Ordovician, Permian, Early Triassic, and Quaternary sediment of the Perth Basin came from Proterozoic orogens. Only the Late Permian sample contains significant populations of Archean (Yilgarn) zircons but whether they came direct from the craton or were recycled from the postulated sedimentary cover is not known. The increased influx of sediment during the Jurassic matched by a peak in the denudation rate would seem to require a primary supply from the craton. This question could be resolved by dating zircon from the rapidly accumulated Jurassic formations. Author Affiliation: GEMOC ARC National Key Centre, Department of Earth and Planetary Sciences, Macquarie University, Sydney NSW 2109, Australia Article History: Received 2 December 2003; Accepted 19 May 2004 Article Note: (footnote) [star] Supplementary data associated with this article can be found, in the online version, at doi: 10.1016/j.earscirev.2004.05.005.

Potassium (K)-rich mafic rocks are viewed as being derived from partial melting of an enriched mantle source, but it is controversial about which processes cause the mantle enrichment. The Fushui intrusive complex is the largest early Paleozoic K-rich intrusive complex in the eastern Qinling orogen. Therefore, detailed studies on the Fushui complex can contribute not only to understanding of the petrogenesis of K-rich mafic rocks, but also to unraveling the Paleozoic evolution of the Qinling orogen. In this study, we provide an integrated investigation of in situ zircon U-Pb dating and Hf-O isotopes, in combination with whole-rock major and trace elements, as well as Sr-Nd-Hf isotopes, for the Fushui intrusive complex. In situ zircon secondary ion mass spectrometry (SIMS)/laser ablation induction coupled plasma mass spectrometry (LA-ICPMS) U-Pb dating reveals that different rock types of the Fushui complex have identical formation ages of 488-484 Ma. The Fushui complex belongs to the shoshonitic series, and is characterized by extreme large ion lithophile element (LILE, e.g., Ba, U, Th and Sr) and Pb enrichment and depletion of high field-strength elements (HFSEs, e.g. Nb, Ta, Zr, Hf, P and Ti). It shows high initial Sr isotopic ratios (0.7100-0.7151), negative whole-rock [ζ.sub.Nd](0 (-3.97 to -5.68) and negative to slight positive whole-rock (-2.24 to 2.38) and zircon (-2.85 to 0.34) [ζ.sub.Hf](t) values, as well as high zircon δ[sup.18]O values (6.86 ± 0.13 ‰). The Hf-Nd isotopic systems are decoupled with positive Δ[ζ.sub.Hf] values (3.85-5.37). These geochemical features indicate that the mantle source has incorporated subducted zircon-barren oceanic sediments. A simple two-endmembers mixing model constrains the amount of subducted sediments in the Fushui mantle source to 5-8 %. The Fushui complex originated from 1 to 6 % equilibrium melting of a phlogopite-bearing garnet lherzolite by non-modal melting. As shoshonitic magmas have been discovered in modern nascent arcs, we suggest that the generation of the Fushui complex was induced by the subduction of the Paleotethyan Ocean, when it jumped from the northern to the southern boundary of the North Qinling microcontinent. Keywords Zircon Hf-O isotope * Geochemistry * K-rich mafic rock * Qinling orogen * Subducted sediment, Introduction Potassium (K)-rich mafic rocks are common, albeit minor, in both orogenic belts and cratons (Foley and Peccerillo 1992; Nowell et al. 2004; Prelevic et al. 2010), and are viewed [...]