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The Park Spur pluton (PSP) is located in the central Cape Breton Highlands, near the eastern margin of the Aspy terrane and its tectonic contact with the adjacent Bras d'Or [...]

Small plutons of mafic to intermediate composition are locally associated with the abundant Devonian granitic plutons that intruded the Goldenville and Halifax groups in the eastern Meguma terrane of mainland [...]

The Castle Frederick prospect is a Pb-Zn play hosted in the granitoid rocks of the Late Devonian (~380-365 Ma) South Mountain Batholith (SMB), within the Meguma terrane, near Upper Falmouth, [...]

The Cape Spencer area is located 15 km southeast of Saint John, New Brunswick. Gold mineralization has been identified mainly in illitized (illite-carbonate [+ or -] quartz [+ or -] [...]

Abstract: The Archean Cote Gold Au(-Cu) deposit is the first large gold deposit discovered in the Swayze greenstone belt of the Abitibi Subprovince. The deposit is a low-grade, large-tonnage type [...]

Geological mapping, petrological studies, and U-Pb (zircon) dating were done to better characterize metasedimentary and metaigneous rock units in the northeastern Aspy terrane, Cape Breton Highlands, Nova Scotia. Foliated biotite [...]

The Wildcat Brook Mo-W deposit is located approximately 9 km east of the former Mt. Pleasant Sn-W-Mo mine in Charlotte County, New Brunswick. It is hosted by a leucocratic, quartz-feldspar [...]

Rock physical properties provide the link between geophysical surveys and their geological interpretation. The British Columbia rock physical properties database, compiled by the Geological Survey of Canada, now comprises 3876 values of density, 930 values of electric resistivity, 12 356 values of magnetic susceptibility, and 2576 values of magnetic remanence and Koenigsberger ratio. The measurements are linked to sample locations, lithologies, and geological formation or unit. Maps, histograms, and biplots are used to demonstrate useful links between lithology and physical properties, and serve as a background for future rock physical properties studies. As expected, density and resistivity are controlled mostly by porosity and mineralogy. Magnetic susceptibility has a bimodal distribution (maxima at 4 x [10.sup.-4] and 2 x [10.sup.-2] SI) controlled by magnetite concentration. Magnetic remanence is shown to be more important than usually considered in magnetic survey analysis, with Koenigsberger ratios greater than unity in 42% of the samples. A case study of the Chilcotin Group basalts is highlighted, as they form a significant barrier to mineral exploration in central British Columbia. These rocks are magnetically distinct from other basalts in British Columbia, distinguished by magnetic susceptibilities having a range of values concentrated around 3 x [10.sup.-3] SI and falling in the valley between the two susceptibility modes. These basalts are also characterized by very high Koenigsberger ratios (96% above unity), probably caused by a preponderance of fine-grained single-domain magnetite. The database provides a wealth of petrophysical properties that can help constrain analysis of several types of geophysical surveys and, in particular, modelling of anomalies in the quest to determine the three-dimensional distribution of rock units. Les proprietes physiques des roches constituent le lien entre les leves geophysiques et leur interpretation geologique. La base de donnees de proprietes physiques des roches de la Colombie-Britannique, compilee par la Commission geologique du Canada, comprend maintenant 3876 valeurs de densite, 930 valeurs de resistivite electrique, 12 356 valeurs de susceptibilite magnetique et 2576 valeurs de remanence magnetique et de rapport de Koenigsberger. Les mesures sont reliees aux sites d'echantillonnage, aux lithologies et aux formations ou unites geologiques. Des cartes, des histogrammes et des diagrammes de double projection sont utilises pour demontrer des liens utiles entre la lithologie et les proprietes physiques; ils servent aussi en tant que cadre de reference pour de futures etudes des proprietes physiques des roches. Tel qu'attendu, la densite et la resistivite sont controlees principalement par la porosite et la mineralogie. La susceptibilite magnetique a une distribution bimodale (maximums a 4 x [10.sup.-4] and 2 x [10.sup.-2] SM) controlee par la concentration en magnetite. La remanence magnetique est demontree etre plus importante que normalement consideree dans les analyses de leves magnetiques avec des rapports de Koenigsberger superieurs a l'unite dans 42 % des echantillons. Une etude de cas des basaltes du Groupe de Chilcotin est mise de l'avant, puisque ces basaltes restreignent fortement l'exploration minerale au centre de la Colombie-Britannique. Ces roches ont un magnetisme distinct des autres basaltes de la Colombie-Britannique; elles ont en effet des susceptibilites magnetiques dont la plage des valeurs est concentree autour de 3 x [10.sup.-3] SM, tombant donc dans le creux entre les deux modes de susceptibilite. Ces basaltes sont aussi caracterises par des rapports de Koenigsberger tres eleves (96 % superieurs a l'unite), probablement en raison de la preponderance de magnetite a grain fin a domaine unique. La base de donnees fournit un tresor de proprietes petrophysiques qui peuvent aider a encadrer l'analyse de plusieurs types de leves geophysiques, particulierement la modelisation des anomalies, dans le but de determiner la distribution idimensionnelle des unites rocheuses. [Traduit par la Redaction], Introduction Geophysical surveys provide a powerful tool for probing three-dimensional distributions of geological units and structures, which otherwise are only revealed through surface or drill-core mapping. They are particularly important [...]

The occurrence of ca. 360 Ma greisen-related molybdenite mineralization in the Clayton Hill biotite-muscovite leucomonzongranite ( La presence d'une mineralisation de molybdenite associee a un greisen de 360 Ma dans le leucomonzongranite a biotite et muscovite (> tapissees de pyrite et enrichies en Cu-As-Bi-Au. Des isotopes stables (O et S) indiquent la formation de greisens a 450°C a partir de fluides dans lesquels δ[sup.18][O.sub.[H.sub.2O]] = 7‰ et δ[sup.34][S.sub.[H.sub.2S]] = 2-3‰, suggerant un reservoir magmatique de type A ou I plutot qu'un magma hyperalumineux. Ces donnees indiquent qu'il s'est produit un evenement magmatique de grande envergure, 20 Ma apres l'evenement Sn-metaux de base, a 380 Ma, dans le sud de la Nouvelle-Ecosse (p. ex. East Kemptville). Cet evenement ayant le meme age que le gisement de classe mondiale Mo-Sn-W-Zn-In de Mt. Pleasant dans le sud du Nouveau-Brunswick indique un potentiel superieur pour une mineralisation importante associee au granite dans cette partie du Canada atlantique. [Traduit par la Redaction], Introduction Examination of the metallogenic map of the Meguma terrane of southern Nova Scotia (Chatterjee 1983) indicates considerable metal endowment (e.g., Sn, W, Au, Zn, Pb, Fe, Ba), with a [...]

ABSTRACT The Late Silurian Landry Brook and Dickie Brook plutons and Charlo plutonic suite underlie a combined area of approximately 80 [km.sup.2] in the northeastern part of the Ganderian Tobique-Chaleur [...]

Fluid inclusions in diagenetic cements in Upper Jurassic--Lower Cretaceous sandstones offshore Nova Scotia provide constraints on the fluid migration history in gas reservoirs of the Scotian basin. Diagenetic minerals from six wells in the Venture field were analysed by optical petrography, scanning electron microscopy (SEM), and electron microprobe. A total of 122 primary and secondary fluid inclusions were analysed from different cements. Primary aqueous inclusions in quartz overgrowths have homogenization temperatures([T.sub.h)] of 111.8 ± 7.1 °C (1σ) and in later carbonate cements 126.5 ± 2.1 °C; inclusions in both cements are highly saline (16-26.1 wt.% NaCl equivalent). Secondary aqueous and hydrocarbonbearing inclusion trails crosscutting silica cement and detrital quartz have [T.sub.h] of 121.6 ± 13.6 °C and low salinities (8.7 ± 6.0 wt.%). Secondary carbonic inclusions have C[O.sub.2] melting temperatures (-56.6 ± 0.1 °C) and [T.sub.h](-9.3 ± 0.8 °C) indicating a high-density carbonic phase. Late carbonate cements in the same sandstone units vary in chemical composition in different wells, and connected reservoirs show similar late carbonate assemblages, suggesting that the late carbonate cementation may be partly controlled by the reservoir fill and spill sequence. Silica and late carbonate cementation involved highly saline fluid flow, likely at about ~135 Ma. Hydrocarbon migration postdated silica cementation and was associated with secondary fracturing, suggesting that it corresponded to the onset of overpressure. Les inclusions de fluides dans les ciments diagenetiques de gres datant du Jurassique superieur--Cretace inferieur au large de la Nouvelle-Ecosse fournissent un cadre pour l'historique de la migration des fluides dans des reservoirs de gaz du bassin neo-ecossais. Des mineraux diagenetiques de six puits dans le champ Venture ont ete analyses par petrographie optique, microscopie electronique a balayage (SEM) et microsonde electronique. En tout, 122 inclusions primaires et secondaires de fluides provenant de differents ciments ont ete analysees. Les inclusions aqueuses primaires dans des excroissances de quartz ont des temperatures d' homogeneisation ([T.sub.h])de 111,8 ± 7,1 °C (1σ) et, dans des ciments carbonates plus tardifs, elles ont des [T.sub.h] de 126,5 ± 2,1 °C; les inclusions dans les deux ciments sont hautement salines (16 a 26,1 % poids en equivalent NaCl). Des trainees d'inclusions porteuses d'hydrocarbures et aqueuses secondaires recoupant le ciment de silice et le quartz detritique ont des [T.sub.h] de 121,6 ± 13,6 °C et de faibles salinites (8,7 ± 6,0 % poids). Les temperatures de fusion du C[O.sub.2](-56,6 ± 0,1 °C) et de [T.sub.h](-9,3 ±0,8 °C) des inclusions carboniques secondaires indiquent une phase carbonique a densite elevee. Les ciments carbonates tardifs dans les memes unites de gres ont des compositions chimiques qui varient selon les differents puits et des reservoirs relies montrent des assemblages carbonates tardifs similaires, suggerant que la cimentation carbonatee tardive puisse etre en partie controlee par la sequence de remplissage et de deversement du reservoir. La silice et la cimentation tardive par des carbonates impliquaient un ecoulement de fluides hautement salins, il y a probablement ~135 Ma. La migration des hydrocarbures a eu lieu apres la cimentation par de la silice et elle est associee a une fracturation secondaire, suggerant qu' elle corresponde avec le debut de la surpression. [Traduit par la Redaction], Introduction Fluid inclusions can record the migration of fluids, including hydrocarbons, through a basin during cement precipitation and microfracture annealing. These can be examined using microthermometry, ultraviolet microscopy, and other [...]

Field, microstructural and anisotropy of magnetic susceptibility (AMS) data from the Palaeozoic Mandi-Karsog pluton in the Lesser Himalayan region reveal a concordant relationship between fabric of the Proterozoic host rock and the granite. The pluton displays a prominent arcuate shape on the geological map. The margin-parallel mesoscopic and magnetic fabrics of the granite and warping of the host rock fabric around the pluton indicate that this regional curvature is either synchronous or pre-dates the emplacement of the granite body. Mesoscopic fabric, magnetic fabric and microstructures indicate that the northern part of the pluton preserves its pre-Himalayan magmatic fabric while the central and southern part shows tectonic fabric related to the Tertiary Himalayan orogeny. The presence of NW-SE-trending aplitic veins within the granite indicates a post-emplacement stretching in the NE-SW direction. Shear-sense indicators in the mylonites along the margin of the pluton suggest top-to-the-SW shearing related to the Himalayan orogeny. Based on these observations, it is envisaged that the extension that gave rise to this rift-related magmatism had a NE SW trend, that is, normal to the trend of the aplite veins. Subsequently, during the Himalayan orogeny, compression occurred along this same NE-SW orientation. These findings imply that the regional curvature present in the Himachal Lesser Himalaya is in fact a pre-Himalayan feature and the pluton has formed by filling a major pre-Himalayan arcuate extension fracture. Keywords: Himalaya, Mandi-Karsog Pluton, granite, anisotropy of magnetic susceptibility, deformation, mylonites. doi: 10.1017/S0016756810000105

Red Cones are a pair of basaltic cinder cones located 5 km SSW of Mammoth Mountain at the southern end of the Mono-Inyo volcanic chain, in eastern California. Charcoal recovered at two separate locations beneath the Red Cones scoria-fall deposits indicates that the eruption most likely occurred shortly after 8490 [+ or -] 90 [sup.14]C yr B.P. and no later than 9325 [+ or -] 83 [sup.14]C yr B.P., which implicates Red Cones as the most recent eruption of basalt in the Mono-Inyo volcanic chain. Results from geologic field mapping combined with geochemical and petrologic analysis suggest that the ca. 8500 yr B.P. eruption produced 10.1 x [10.sup.6] [m.sup.3] of magma, possibly beginning from south Red Cone and later from north Red Cone via Hawaiian, Strombolian, and violent Strombolian eruptions over a minimum of 28 days. All deposits contain plagioclase, olivine, clinopyroxene, chrome-spinel, and titanomagnetite. Material erupted from each cone can be classified as high-aluminum basalts that exhibit calc-alkaline differentiation trends and belong to the medium-K series. Red Cone basalt samples are generally similar in terms of many major and trace element concentrations, but south Red Cone samples typically contain more Si[O.sub.2], Sr, Zr, Rb, and Ba, and less MgO, FeO, CaO, Ni, and Cr than north Red Cone samples. Clinopyroxene-liquid thermobarometry calculations indicate that the majority of Red Cones clinopyroxene crystal cores crystallized at temperatures of 1160-1210[degrees]C and pressures equivalent to 10-25 km depth, which supports the possibility of a basaltic dike and sill plexus located 10-25 Ion beneath the west and southwest flanks of Mammoth Mountain. doi: 10.1130/B30070.1

Petrologic, chemical, and polytype data are presented for dioctahedral potassic micas from Kfeldspar-bearing metamorphic and igneous rocks of acidic composition unaffected by high-pressure (HP) conditions. The paper aims to demonstrate that: (1) under non-HP conditions, in both metamorphic and igneous plutonic environments, a given bulk-rock compositional constraint imposes a more or less marked phengitic composition to dioctahedral potassic mica; and (2) this muscovite crystallizes as [2M.sub.1], notwithstanding its phengitic composition. The samples (157 in number) are from widespread provenances. We conclude that the growth of 3T polytype of muscovite is not a function of mica composition. This is consistent with the recent crystallographic knowledge on polytypism, cation ordering, elastic properties, and structural deformational mechanisms of muscovite, which address the stabilization of 3 T with pressure. Keywords: Muscovite, phengite, celadonitic substitution, polytypism, [2M.sub.1], 3 T, pressure-polytype relationship, mica chemistry, polytype relationship, petrologic mineralogy DOI: 10.2138/am.2010.3362

Laser ablation inductively coupled plasma mass spectrometry zircon U--Pb dating and geochemical data document the Early Devonian Sandaogou alkaline complex (409 Ma) from the northern margin of the North China craton. The rock suite includes pyroxene syenite, quartz syenite and monzonite. These rocks exhibit high contents of [K.sub.2]O (5-13 wt%), strong enrichments in large ion lithophile elements and light REE, slightly negative Eu anomalies, and pronounced depletions in high field strength elements. They are characterized by moderate [sup.87]Sr/[sup.86][Sr.sub.i] ratios of 0.7052-0.7071, low [[epsilon].sub.Nd](t) values of - 12.7 to -17.9 and zircon [[epsilon].sub.Hf](t) values from -27.8 to -32.3. These geochemical features and quantitative isotopic modelling suggest that they might have been formed through simultaneous fractional crystallization and lower crustal assimilation of a metasomatized mantle-derived alkali basaltic magma. These trachytic rocks, together with the Middle Devonian alkaline rocks and mafic--ultramafic complex from neighbouring regions, constitute a linear post-collisional magmatic belt along the northern North China craton, possibly formed under a tectonic regime of slab breakoff. They serve not only as a magmatic milestone for marking the termination of Early Palaeozoic orogenic cycle around the northern North China craton, but also as a spatial tracer for locating the position of the potential ancient slab breakoff at the surface. Supplementary material: Analytical methods, mineral composition data, field and zircon cathodoluminescence (CL) photographs are available at http://www.geolsoc.org.uk/SUP18403. doi: 10.1144/0016-76492009-110.

The mineral wadalite (ideal and simplified formula: [Ca.sub.6][Al.sub.5][Si.sub.2][O.sub.16][Cl.sub.3]) has been discovered for the first time in a meteorite, specifically in coarse-grained, igneous type B calcium-aluminum-rich inclusions (CAIs) from the CV carbonaceous chondrite Allende. We report the results of electron microprobe, scanning electron microscopy, and transmission electron microscopy analyses of wadalite-bearing assemblages in the Allende CAIs and propose that wadalite formed by metamorphic reaction between akermanitic melilite and anorthite, likely mediated by chlorine-bearing fluids. Petrographic relationships support the likelihood of multistage alterations by fluids of different chemistries interspersed or coinciding with thermal metamorphic episodes on the Allende parent asteroid. Fluid involvement in metamorphism of Allende CAIs implies that these objects experienced open-system alteration after accretion into the CV chondrite parent asteroid, which may have resulted in disturbances of their oxygen- and magnesium-isotope systematics. Keywords: Wadalite, Allende, type B CAIs, aqueous alteration, fluid-mediated metamorphism DOI: 10.2138/am.2010.3296

The recent discoveries of large, active populations of microbes in the subseafloor of the world's oceans supports the impact of the deep biosphere biota on global biogeochemical cycles and raises important questions concerning the functioning of these extreme environments for fife. These investigations demonstrated that subseafloor microbes are unevenly distributed and that cell abundances and metabolic activities are often independent from sediment depths, with increased prokaryotic activity at geochemicai and/or sedimentary interfaces. In this study we demonstrate that microbial populations vary at the scale of individual beds in the biogenic oozes of a drill site in the eastern equatorial Pacific (Ocean Drilling Program Leg 201, Site 1226). We relate bedding-scale changes in biogenic ooze sediment composition to organic carbon (OC) and microbial cell concentrations using high-resolution color reflectance data as proxy for lithology. Our analyses demonstrate that microbial concentrations are an order of magnitude higher in the more organic-rich diatom oozes than in the nannofossil oozes. The variations mimic small-scale variations in diatom abundance and OC, indicating that the modern distribution of microbial biomass is ultimately controlled by Milankovitch-frequency variations in past oceanographic conditions. doi: 10.1130/G30207.1

ABSTRACT Machias Seal Island in the northern Gulf of Maine consists of fine- to medium-grained weakly foliated quartz monzodiorite. Although previously inferred to be as young as Devonian, the quartz [...]

The Late Palaeozoic volcanic rocks, mainly consisting of basalt, trachyte, trachy-andesite, andesite and rhyolite, widely distributed in the southwestern Tianshan Mountains, have been proven to be formed during Late Devonian to Late Carboniferous time (>361-313 Ma) based on zircon sensitive high-resolution ion microprobe dating. The geochemistry demonstrates that the studied volcanic rocks represent a continental arc formed during the subduction of the Palaeo-southern Tianshan Ocean. The [[epsilon].sub.Hf(t)] values of zircons in these volcanic rocks vary from +1.4 to +15.6 with weighted average values of +9.5 (Late Devonian), +8.9 (Early Carboniferous) and +10.3 (Late Carboniferous), suggesting a depleted mantle origin. However, the Late Devonian basaltic samples have negative [[epsilon].sub.Nd(T)]) values (from -5.16 to 3.07) and high initial [sup.87]Sr/[sup.86]Sr ratios (0.7073-0.7098), whereas the Early Carboniferous volcanic rocks mostly have positive [[epsilon].sub.Nd(T)] values (from 0.18 to +3.07) with low initial [sup.87]Sr/[sup.86]Sr ratios (0.7044-0.7067), and the Late Carboniferous volcanic rocks are characterized by high [[epsilon].sub.Nd(T)] values (+2.79 to +5.89) and low initial [sup.87]Sr /[sup.86]Sr ratios (0.7032-0.7054). The assimilation-fractional crystallization (AFC) model is used to explain the isotope characteristics of the Late Devonian volcanic rocks in the southwestern Tianshan Mountains. Calculation shows that the Late Devonian samples could be formed by the AFC process between depleted mantle and continental crust. The Carboniferous basaltic rocks originated by partial melting of the mantle wedge. Supplementary material: Data are available at http://www.geolsoc.org.uk/SUP18378. doi: 10.1144/0016-76492008-130.

Ivanyukite-Na-T, [Na.sub.3][[Ti.sub.4](OH)[O.sub.3](Si[O.sub.4]).sub.3]]*7[H.sub.2]O, ivanyukite-Na-C, [Na.sub.2][[Ti.sub.4][O.sub.2][(OH).sub.2](Si[O.sub.4]).sub.3]] * 6[H.sub.2]O, ivanyukite-K, [K.sub.2][[Ti.sub.4][(OH).sub.2][O.sub.2](Si[O.sub.4]).sub.3]] * 9[H.sub.2]O, and ivanyukite-Cu, Cu[[Ti.sub.4][(OH).sub.2][O.sub.2] [(Si[O.sub.4]).sub.3]] * 7[H.sub.2]O, are new microporous titanosilicates found in a natrolitized microcline-aegirine-sodalite lens in the orthoclase-bearing urtite at the Koashva Mountain (Khibiny Massif, Kola Peninsula, Russia). The minerals occur as well-shaped colorless (ivanyukite-Na-T), paleorange (ivanyukite-Na-C), pale-blue (ivanyukite-K), and green (ivanyukite-Cu) cubic crystals (up to 1.5 mm in diameter) grown on mierocline, vinogradovite, sazykinaite-(Y), natrolite, and djerfisherite. The minerals have vitreous luster and white streak. They are transparent and non-fluorescent. The Mohs hardness is estimated as ~4. The minerals are brittle. Cleavage is perfect on {100} (ivanyukite-Na-C, ivanyukite-K, and ivanyukite-Cu) or on {1011} (ivanyukite-Na-T), fracture is steppe& Density, measured by the sink/float method in heavy liquids, ranges from 2.60 (ivanyukite-Na-C) to 2.70 g/[cm.sup.3] (ivanyukite-Na-T, ivanyukite-K, and ivanyukite-Cu), whereas calculated densities are: 2.58 (ivanyukite-Na-T), 2.39 (ivanyukite-Na-C), 2.69 (ivanyukite-K), and 2.46 g/[cm.sup.3] (ivanyukiteCu). Ivanyukite-Na-T is uniaxial (+), [n.sub.[omega]] = 1.76(1), [n.sub.[epsilon]] = 1.85(9) (589 nm), and the other minerals are isotropie, n = 1.73(1). Chemical analysis by electron microprobe gave (wt% for ivanyukite-Na-T, ivanyukite-Na-C, ivanyukite-K, and ivanyukite-Cu, respeetively): [Na.sub.2]O 7.46, 5.19, 0.27, and 0.17; [Al.sub.2][O.sub.3] 0.07, 0.21, 0.18, and 0.07; Si[O.sub.2] 23.75, 25.47, 23.16, and 24.80; S[O.sub.3] 0.00, 0.00, 0.00, and 0.20; [K.sub.2]O 5.89, 6.34, 7.09, and 6.81; CaO 0.21, 0.14, 0.95, and 0.23; Ti[O.sub.2] 38.89, 37.81, 36.14, and 38.36; MnO 0.05, 0.33, 0.68, and 0.28; FeO 0.54, 2.17, 0.37, and 0.73; CuO 0.00, 0.00, 2.21, and 6.81; SrO 0.00, 0.00, 0.19, and 0.00; [Nb.sub.2][O.sub.5] 2.99, 2.90, 3.62, and 3.02; BaO 0.14, 0.00, 0.00, and 0.00; [H.sub.2]O (by the Penfield method) 19.00, 19.15, 25.00, and 21.50; total 98.99, 99.71, 99.86, and 98.97. The empirical formulae (based on Si+Al = 3 apfu) are [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII.] 7.21[H.sub.2]O (ivanyukite-Cu). Ivanyukite-Na-T is trigonal, R3m, a = 10.94(2), c = 13.97(4) [Angstrom], Z = 3. Other minerals are cubie, P43m a = 7.856(6) (ivanyukite-Na-C), 7.808(2) (ivanyukite-K), and 7.850(7) [Angstrom] (ivanyukite-Cu); Z = 1. The strongest lines in the powder X-ray diffraetion pattern [[d.sub.bs]([Angstrom]) ([I.sub.obs]) hkl] are: 7.88(100) (011), 3.277(60)(014), 3.175(80)(212), 2.730(50)(220), 2.607(70)(303), 2.471(50)(124), 1.960(60)(044), 1.916(50) (135) (ivanyukite-Na-T); 7.88(100)(100), 4.53(30)(111), 3.205(80)(211), 2.774(30)(220), 2.622(40)(221,300), 2.478(40)(310), 1.960(30)(400), 1.843(30)(330, 411) (ivanyukite-Na-C); 7.85(100)(100), 3.91(20)(200), 3.201(80) (211), 2.765(20)(220), 2.602(30)(221,300), 2.471(40)(310), 1.951(30)(400), 1.839(30)(330, 411) (ivanyukite-K); 7.87(100)(100), 3.94(20)(200), 3.205(80)(211), 2.774(20)(220), 2.616(30)(221, 300), 2.481(30)(310), 1.960(30) (400), 1.843(30)(330, 411) (ivanyukite-Cu). The crystal structure ofivanyukite-Na-T [trigonal, R3m, a = 10.921(3), c = 13.885(4) [Angstrom], V = 1434.2(7) [[Angstrom].sup.3]] has been solved from highly mosaic crystal and refined to [R.sub.1] = 0.147 on the basis of 723 unique observed reflections. The crystal structures of ivanyukite-group minerals are based upon a 3-dimensional framework of the pharmacosiderite type, consisting of four edge-sharing Ti[O.sub.6]-octahedra interlinked by Si[O.sub.4] tetrahedra. The framework has a 3-dimensional system of channels defined by 8-membered rings with an effective channel width of 3.5 [Angstrom] (caleulated as the distance between O atoms across the channels minus 2.7 [Angstrom]). The channels are occupied by [Na.sup.+] and [K.sup.+] cations and [H.sub.2]O molecules. The infrared spectra of the ivanyukite group minerals show 14 absorption bands caused by vibrations of Si-O and Ti-O bonds, molecular water, and [(OH).sup.-] groups. Ivanyukite Na-T formed as a late-stage, hydrothermal phase of ultra-agpaitic hydrothermalites; ivanyukite-Na-C is produced by partial hydration of ivanyukite-Na-T, and both ivanyukite-K and ivanyukite-Cu are produced by partial hydration of ivanyukite-Na-T and natural cation exchange of Cu for Na near dissolved djerfisherite and chalcopyrite grains. Nomenclature of the ivanyukite group is based on the dominant extraframework cation and symmetry of the crystal structure. The minerals are named in honor of Gregory Yur'evich Ivanyuk, Russian mineralogist and petrologist, head of the Laboratory of Self-Organized Mineral Systems in the Geological Institute of the Kola Science Centre of the Russian Academy of Sciences, for his contributions to the petrology and mineralogy of banded iron-formations, alkaline, and alkaline-ultrabasic massifs. Keywords: Ivanyukite-Na-T, ivanyukite-Na-C, ivanyukite-K, ivanyukite-Cu, new mineral, microporous titanosilicate, crystal structure, ultra-alkaline hydrothermalite, cation exchange, Khibiny massif, Kola Peninsula

Quartz solubility in [H.sub.2]O-C[O.sub.2] fluids was measured at 800[degrees]C and 10 kbar. Mixed fluids were generated from hydrous oxalic acid, silver oxalate, silver carbonate, and liquid [H.sub.2]O; solubility was determined by weight changes of the quartz crystals. Stringent blank tests and weighing procedures were used to establish the C[O.sub.2] and [H.sub.2]O contents of experimental fluids. Using experimentally constrained models of [H.sub.2]O activity and mixing of silica monomers and dimers, a logarithmic plot of monomer activity vs. [H.sub.2]O activity yields a linear data array of constant slope n insignificantly different from 4 (n = 4.024, [R.sup.2] = 0.997), where n is the total monomer hydration number. Moreover, all high-quality quartz solubility data in [H.sub.2]O-C[O.sub.2] fluids at lower temperature and pressure fall on the same line when Si[O.sub.2] and [H.sub.2]O activities are calculated with this formulation. The same analysis for the dimer yields slope n of 7 (n = 7.049, [R.sup.2] = 0.996). Our results show that neutral silica monomers and dimers have fixed stoichiometry of Si[(OH).sub.4]*2[H.sub.2]O and [Si.sub.2]O[(OH).sub.6]*4[H.sub.2]O (i.e., two solvating [H.sub.2]O molecules per Si) in [H.sub.2]O-C[O.sub.2] fluids for a large range of crustal metasomatic processes. This provides a simple basis for modeling [H.sub.2]O-C[O.sub.2]-Si[O.sub.2] fluids over a range of pressure, temperature, C[O.sub.2], and Si[O.sub.2] activity. Keywords: Quartz solubility, crustal fluids, experimental petrology, thermodynamics

Fifty years ago, geologic conditions attending the formation of blueschists, eclogites, and garnet lherzolites were not known. But, with the advent of high-pressure phase-synthesis equipment and precise calorimetry, minerals like jadeite, aragonite, pyrope, and the dense polymorphs of Si[O.sub.2] and C were shown to be stable at elevated pressures and relatively low temperatures. Metamorphic conditions required by P-T stabilities of these minerals reflect the operation of plate tectonics, lithospheric subduction, and inferred mantle convection. Integration of phase equilibria with dynamic tectonic processes has illuminated the petrogenesis of the crust. Combined with geochemical, geophysical, and isotopic data, high-pressure phase equilibria are also providing new constraints on the constitution and evolution of the mantle. Circumpacific blueschists and eclogites occur in penetratively sheared nappes that are overturned seaward, indicating 30-50 km descent of an oceanic plate during metamorphism before partial exhumation of mainly low-density crustal material. Neoblastic coesite and microdiamond inclusions in tough, rigid host minerals show that continental collision involves fragmentary recovery of subducted rocks from depths of 100-130 km, far deeper than traditionally thought. Even more surprising, garnet peridotites from the central Alps, western Norway, Bohemia, and China display intergrowths and exsolution lamellae reflecting the former existence of majoritic garnet, stishovite, and other phases requiring depths of origin >300 km. Exsolved nanominerals attest to the decompression of precursor phases that had formed at profound depths preceding mantle upwelling. Times of deep-seated storage and rates of exhumation remain as major problems. Fluid-rock and lithosphere-asthenosphere interactions have recycled volatiles to the deep Earth through subduction of both hydrous and nominally anhydrous minerals. Mantle petrochemistry and plume-plate dynamics control the evolving architecture of the Earth's crust and the interdependent biosphere. Applications of advanced technologies to condensed materials are leading to a fuller understanding of the planetary interior in time and space. Keywords: Metamorphic petrology, high-pressure belts, phase equilibria, subduction-zone belts, high-pressure studies, convergent plate junctions, thermobarometry, ultrahigh-pressure rocks

Significant quantities of silver can be accommodated in galena as a coupled substitution with Ag + Sb and/or Ag + Bi for 2 Pb atoms. The limitations of this solubility are quantified experimentally for the cubic (Fm[bar.3]m) [alpha]-galena phase. Above 441.7 [degrees]C, the [alpha]-galena phase has complete solid solution across the [Pb.sub.2][S.sub.2]-AgSb[S.sub.2]-AgBi[S.sub.2] (galena-miargyrite-matildite) ternary. Dry sinter experiments at 400, 375, and 350 [degrees]C extend the known miscibility gap on the [Pb.sub.2][S.sub.2]-AgSb[S.sub.2] binary into ternary compositions. Phase equilibrium and miscibility gap data and self-consistent thermodynamic data for other high-temperature phases in this system combined with data for other sulfides and sulfosalts are used to constrain an asymmetric regular solution model for the [alpha]-galena phase ([Pb.sub.2],AgSb,AgBi) [S.sub.2]. Phase relations in this system suggest that simple retrograde re-equilibration during cooling can produce phase assemblages and textures commonly observed in Ag-bearing ore deposits. Bulk metal ratios of deposits in conjunction with the application of this thermodynamic model may be used to understand district Ag-distribution or as an exploration tool. Keywords: Experimental petrology, Ag in galena, phase equilibria, thermodynamics, silver deposits

The Peloritani Mountains constitute the Sicilian portion of the Calabria--Peloritani Arc (Italy), a tectono-metamorphic edifice recording the history of the subduction--exhumation cycle during Tertiary convergence between the African and European plates. Here, we describe the kinematic and the petrological characteristics of the major shear zones bounding the lowermost continental-derived metamorphic units cropping out in the eastern portion of the Peloritani Mountains. Both meso-and micro-scale shear sense criteria indicate a top-to-the-SSE tectonic transport, during a general evolution from ductile to brittle deformation conditions. Quantitative thermobarometry on texturally equilibrated phengite-chlorite pairs crystallized along the shear bands indicates pressure of 6-8 kbar at temperatures of 360-440 [degrees]C for the structurally highest units and 3-4 kbar at 380-440 [degrees]C for the lowest ones. This documents an overall inverse-type nappe arrangement within the tectonic edifice and a transition from an Alpine-(13-18 [degrees]C [km.sup.-1]) to a Barrovian-type (28-36 [degrees]C [km-.sup.1]) geothermal gradient during the progress of the Alpine orogenic metamorphism in the Peloritani Mountains. The integration of these results allows the Peloritani Mountains to be considered as a constituent element of the Apennine orogenic domain formed during the progressive space--time transition from oceanic to continental subduction at the active convergent margin. Keywords: Alpine metamorphism, metamorphic petrology, continental subduction, Peloritani Mountains, Calabria--Peloritani Arc.

Altan Uul and Nemegt Uul are mountain ranges in southern Mongolia containing polydeformed Mid- to Late Palaeozoic sedimentary, volcanic and metamorphic rocks uplifted at a restraining bend along the Gobi--Tien Shan left-lateral strike-slip fault system. Altan and Nemegt Uul contain part of an intra-oceanic island arc that was active during the Carboniferous. Thrust-bound sequences of highly fractured pillow basalt, cumulate gabbro, peridotite, serpentinite and jasperoid occur directly north of the arc rocks in at least three discrete belts and are interpreted to be fragments of an ophiolite. Metamorphosed marine sediments that have undergone intense contractional strain lie north of, and structurally below, the ophiolitic rocks. The gabbros within the ophiolitic sequences have undergone prograde metamorphic reactions consistent with an oceanfloor environment, and trace element analyses are similar to those from cumulate gabbros of the Oman ophiolite. Combined field and petrological evidence suggests that there is an east--west-trending south-dipping Late Carboniferous suture in Altan and Nemegt Uul that may be regionally correlated in the southern Gobi Altai region. This proposed suture represents a new and important tectonic boundary between tectonostratigraphic terranes in southern Mongolia, requiring modification of existing models of Late Palaeozoic terrane accretion in the Central Asian Orogenic Belt.

Miocene volcanic rocks in the Pinacate area, Sonora, record a progressive change in the source of magmatism induced by asthenospheric upwelling and lithospheric thinning. [sup.40] Ar/[sup.39] Ar age data, mineral chemistry, and major- and trace-element contents allow the identification of two volcanic sequences: an oldest basaltic episode (ca. 20 Ma), and a middle Miocene (12-15.5 Ma) sequence that consists of mesa basalts with transitional alkali character, calc-alkaline dacites, and high-silica rhyolites evolving toward peralkaline liquids. Sr, Nd, and Pb isotope ratios reveal different sources for the Miocene basalts. The easternmost basalts have signatures indicating a Precambrian lithospheric mantle source, while the westernmost tholeiitic to transitional basalts are related to mixing of lithospheric and asthenospheric mantle. Rhyolites are the result of fractional crystallization of transitional basalt magmas with slight contamination by Precambrian crust. Chemical modeling shows that peral kaline rhyolites are related to slightly higher assimilation during their residence in the upper crust but also to a change in the mantle source of the parent basalt. The evolution of the isotopic signatures in space and time indicates that: (1) the volcanic activity is located over a major lithospheric boundary, i.e., the western limit of the North American Craton; (2) the lithosphere was progressively thinned so that huge volumes of alkalic basalts could access the surface during the Quaternary, building the Pinacate Volcanic Field. Correlation between geochemical signatures and the tectonic evolution of the western margin of the North American Craton shows that a progressive change in the source of magmatism can be related to the development of a slab window during the Miocene. Keywords: Volcanism, Mexico, geochronology, petrology, geochemistry, isotopes.

Abstract: New Rb-Sr phlogopite and U-Pb perovskite age determinations for 12 of 38 known ultramafic bodies in the Buffalo Head Hills area of north-central Alberta show that kimberlitic magmatism occurred [...]

[1] Tertiary convergence, high-pressure-lowtemperature (HP-LT) metamorphism and subsequent exhumation in the internal Western Alps were concurrent with detrital deposition in foreland basins at the external periphery of the orogen. In the present work we have probed the geochronology and chemistry of white mica grains and metamorphic pebbles from the foreland basins of SE France in order to gain additional perspective on exhumation rates and mountain building processes in the internal domain of the Tertiary orogen. Our data indicate that throughout the Tertiary these basins were mainly fed from a relatively low pressure source, dominated by Si-poor micas yielding pre-Alpine [sup.40]Ar/[sup.39] Ar ages. Small amounts of detritus composed of high-pressure minerals and pebbles are first detected in early Oligocene (~30-32 Ma) strata of the Barreme basin. The [sup.40]Ar/[sup.39]Ar geochronology of phengites from garnet-blueschist pebbles from these strata yielded 34 [+ or -] 3 Ma ages indicating rapid ascent and exposure of HP-LT rocks in the internal part of the orogen shortly after metamorphism. To explain the preponderance of pre-Alpine micas alongside the rare presence of Alpine HP-LT detritus we suggest that the general architecture of the Western Alps, whereby inner HP-LT metamorphic units are cut off from the SE France basins by a low-grade lid of Brianconnais back thrusts, was rapidly built in the early Oligocene and did not change significantly since then. Citation: Morag, M., D. Avigad, Y. Harlavan, M. O. McWilliams, and A. Michard (2008), Rapid exhumation and mountain building in the Western Alps: Petrology and [sup.40]Ar/[sup.39]Ar geochronology of detritus from Tertiary basins of southeastern France, Tectonics, 27, TC2004, doi: 10.1029/2007TC002142.

The formation of sillimanite, under metastable conditions, relative to corundum and quartz has been defined experimentally, approximately 700 to 800 MPa inside the kyanite stability field thereby allowing for the approximate location of the metastable Sil = Cnd + Qtz equilibrium to be outlined in P-T space from 600 to 800 [degrees]C. Experiments involved using a NaCl assembly with a graphite furnace in a two-piston-cylinder apparatus. The thermocouple tip was in direct contact with the flat-lying, folded Pt capsule thereby minimizing thermal gradients to Keywords: Sillimanite, kyanite, corundum, quartz, rate of reaction, experimental petrology, Rietveld refinement, aluminosilicates

The Neoproterozoic mafic rocks in western Hunan, South China, form a NNE-striking mafic rock belt for which outcrops are found predominantly in Guzhang, Qianyang and Tongdao. Samples from Qianyang and Tongdao yielded ion microprobe U--Pb zircon ages of 747 [+ or-] 18 Ma and 772 [+ or-] 11 Ma, respectively. The mafic rocks are geochemically divided into two subtypes. Ultramafic rocks from Tongdao are depleted in Nb and Ti, with decoupled Nd--Hf isotopes, and geochemical features similar to the c. 761 Ma mafic--ultramafic rocks from Longsheng, northern Guangxi. Their [[epsilon].sub.Nd](t) value is -2.91, implying an enriched mantle source. Alkaline mafic rocks from Qianyang and Guzhang have high values of Ti[O.sub.2], total alkali, some high field strength elements and [(La/Yb).sub.N], and low Zr/Nb, La/Nb, Sm/Nd and [[sup.143]Nd/.sup.144]Nd ratios as well as coupled Nd--Hf isotopes. They are geochemically similar to ocean island basalts and show fractional crystallization of Fe--Ti oxides, olivine and pyroxene in the mafic magma. The c. 760 Ma mafic rocks in western Hunan may be the products of post-orogenic magmatism. After the Jinningian (Sibao) orogenic process, the upwelling of the deep asthenospheric mantle caused by the break-off and detachment of the subducted oceanic slab led to extension in the area. The extension might have taken place earlier in the Tongdao and Longsheng areas, which led to the partial melting of the lithospheric mantle that had been metasomatized during early oceanic subduction to generate a relatively large amount of sub-alkaline rocks. However, the less alkaline mafic rocks in Qianyang and Guzhang might have been generated in the relatively later stage of the extension, and may have resulted from a small degree of partial melting of the asthenospheric mantle. Keywords: mafic rocks, petrogenesis, post-orogenic extension, Neoproterozoic, South China.

A 50 m drill core (core no. 383-334) collected from the contact metamorphic aureole in the Mouat Ni-Cu prospect in the Mountain View area of Stillwater County, Montana, exhibits evidence of in situ fluid-absent biotite dehydration melting and local back reaction of melts derived from metasediments and metavolcanics. The drill core was investigated to characterize the mineral assemblages and their textures, to search for evidence of partial melting, and to determine mineral and whole-rock geochemistry to provide an understanding of the petrogenesis of the homfels close to the contact with the Stillwater Complex. The rocks investigated are predominantly quartz-plagioclase-cordierite-orthopyroxene-biotite [+ or -] spinel hornfels, Fe-Cu-Ni sulfides, and Fe-Ti oxides. One sample contains garnet ([Alm.sub.73-77][Pyr.sub.20-17][Sps.sub.3][Grs.sub.4]) in addition to cordierite. Three samples contain cordierite-hercynite symplectites surrounded by a narrow mantle devoid of orthopyroxene, plagioclase, and biotite that are roughly ovoid to lenticular in shape. Partially melted samples show back reaction between crystallizing melt and restite such that retrograde skeletal intergrowths of biotite and quartz in the mesosome were developed. Average T-P conditions of hornfels and melt genesis are 786 [degrees]C and 3.7 kbar. Back reactions that produced biotite occurred at somewhat lower temperatures. Whole-rock geochemistry suggests that the protolith of the hornfelsic rocks was likely a mixture of greywacke and additional intermediate to marie volcanogenic components. Keywords: Stillwater Complex, hornfels, partial melting, back reactions

The trace element compositions of aplite dikes in the Sierra Nevada batholith of California differ profoundly from high-silica rhyolites (HSRs) and contradict a genetic connection to them. The aplites are strongly depleted in all middle rare earth elements (REEs), whereas HSRs are strongly depleted only in Eu and enriched in other REEs; the aplites are strongly depleted in Y and variably enriched in Sr, whereas HSRs are enriched in Y and strongly depleted in Sr. Volcanic rocks with the trace element characteristics of these aplites are rare to absent in the geologic record. Aplite REE patterns are likely controlled by titanite, which has large distribution coefficients for REEs, whereas HSRs cannot have equilibrated with titanite. Titanite may crystallize late in dacitic magma and thus HSR may be extracted before titanite saturation is reached; aplites would form after titanite appears, but when the melt percentage is too low and the water content of the melt too high (at fluid saturation) for the magma to ascend without rapid crystallization, thus preventing eruption. HSRs could also form by low-degree partial melting of granodiorite plutons in which titanite melts out early. Alternatively, HSRs may be extracted from silica-rich plutons that lack titanite; leucogranite plutons with REE contents that could be complementary to HSRs are present but uncommon in the Sierra Nevada. Keywords: igneous petrology, geochemistry, California, Sierra Nevada, rare earth elements.

A significant portion of the continental crust of northern Eurasia is thought to have formed during the evolution of the Central Asian Orogenic Belt at the time of accretion of continental terranes and island arcs. Records of this event are well preserved within the Siberian craton-Central Asian Orogenic Belt transition zone in Lake Baikal region, particularly in the Olkhon terrane. Our results establish granulite-facies conditions for peak metamorphism in the Olkhon terrane, and indicate that the granulites were derived from island arc mafic volcanic rocks and back-arc basin sediments. Sensitive high-resolution ion microprobe dating of metamorphic zircons from two mafic granulites yielded [sup.238]U/[sup.206]Pb ages of 507 [+ or -] 8 and 498 [+ or -] 7 Ma, and magmatic zircons from syntectonic syenite yielded an age of 495 [+ or -] 6 Ma. The main metamorphic event occurred at about 500 Ma, and was probably related to collision of the Barguzin microcontinent with the Siberian craton. Ages from 535 to 2750 Ma for detrital zircon cores in early Palaeozoic metasediments of the Olhkon terrane were obtained. Archaean ages of detrital zircons in such metasediments suggest that the Barguzin microcontinent was originally part of the Aldan Province of the Siberian craton that was detached in late Mesoproterozoic, and reattached to the craton during early Palaeozoic collision.

Xenoliths from Hawk's Nib (Bute, SW Scotland), entrained in alkali basalt of late Carboniferous early Permian age, generally possess unrecrystallized igneous cumulate textures. Most are inferred to derive from lower crustal (20-30 km) depths, with a small minority from the underlying restitic mantle. Compositions range from ultramafic cumulates (dunite, wehrlite, websterite, clinopyroxenite) to gabbros and anorthosites. The suite is unique in being dominated by poikilitic wehrlites and olivine clinopyroxenites. Major element variation in the cumulates is controlled by modal mineral variations. The ultramafic cumulates all have high REE contents and light REE (LREE)-enriched patterns, with websterites being the least enriched. Gabbroic xenoliths have uniform patterns in which both LREE and heavy REE are depleted relative to the middle REE, with small positive Eu anomalies. Present-day Sr-Nd isotopic data for the suite are the most depleted among Scottish xenoliths. The xenoliths are inferred to be products of young replenishments of the lower crust by basaltic magmas during continental underplating. Orthopyroxene-bearing lithologies crystallized from tholeiitic magmas whereas alkali basalts formed the elinopyroxene-rich samples; both parental magma-types were derived from similar mantle sources.

The Mount Whitney Intrusive Suite is a nested intrusion composed of three granitic plutons that were emplaced along the eastern margin of the Sierra Nevada batholith between 88 and 83 Ma. Geologic relations indicate the suite was formed by magmas that spread laterally at a depth of ~10 km after initially rising along fractures developed at an extensional stepover between the proto--Kern Canyon fault and the Sierra Crest shear zone. Cenozoic uplift and erosion have exposed the interior of the suite, making it possible to study textural and compositional variations within the body that yield insights into the complementary roles of source variability and crystal fractionation in producing zoned intrusions. Although isotopic data indicate that contributions to the Mount Whitney Intrusive Suite from preexisting crustal rocks increased over time, major differences in the compositional and textural zoning of its members also reflect gradual warming of the upper crust. The oldest pluton is isotopically and compositionally diverse, and consists of distinct phases that apparently underwent limited mixing and fractionation following their emplacement into cool host rocks. Conversely, the younger members are more isotopically uniform, and the youngest displays regular pluton-scale variations in composition and texture consistent with individual inputs having mixed, fractionated, and undergone textural coarsening as it cooled slowly within the older members or wall rocks warmed by them. A thermal model of the suite indicates that the intervals during which successive magma inputs were likely to hybridize and undergo subsequent in situ differentiation increased as the intrusion grew. For recharge at an interval intermediate between those required for 50% crystallization in different parts of the suite, model results suggest that the outer part would have developed as a composite body in which individual phases underwent limited differentiation, whereas the inner part would have developed as a more homogeneous body capable of large-scale differentiation. These predictions match trends among the suite's members and suggest that warming of the upper crust may account for much of its textural and compositional diversity. Local differentiation also occurred in the upper parts of the younger members, where rhyolitic melts were segregated as a result of solidification front instability. Keywords: Sierra Nevada batholith, Mount Whitney Intrusive Suite, pluton, crystal fractionation, emplacement, thermal modeling

The main mineralogical/lithological composition of the Varzaneh aeolian sands is sedimentary and igneous lithics. The minor one is metamorphic lithics and mineral grains (such as quartz, feldspar and heavy mineral grains) respectively. The origin of the sedimentary lithics (mainly carbonates) mostly is from sedimentary rocks exposed in the west and the southwest of the study area. These rocks belong to Cretaceous and Jurassic outcrops. The origin of the igneous lithic grains chiefly belongs to Tertiary highlands, located to the north and the northeast of the study area. The main origin of the metamorphic lithic grains is from the mountain ranges located in the north-western and the western part of the drainage basin of the Zayandeh river. Texture of the aeolian sand grains is similar to the Zayandeh river sediments. Concentration of the aeolian sands at the west of the Zayandeh river delta, variation of their mineralogical/lithological composition from north to south, and textural characterizations of sand grains indicate that the water laid sediments of the Zayandeh river, widespread to the north of the aeolian sands, are the main supply of the aeolian sands and sediments deposited by the two ephemeral streams in the south and the southwest of the sand dunes are minor one. Key words: aeolian sand, lithic grains, mineralogical composition, texture, sediments, INTRODUCTION The term provenance, in general, refers to a location of origin, where the sediments are derived from, and the nature of source rocks (2). In provenance studies, however, it [...]

The distribution of major, minor and trace elements in the Cenozoic alkali basalt from north-eastern Jordan indicates a homogeneous lava flow from a mantle source. These basaltic rocks contain abundant upper mantle xenoliths (spinal lherzolite, harzburgile and olivinewebsterite). Theses xenoliths contain olivine, orthopyroxne, clinoporoxene and a few amounts of spinal. Their mineral assemblages, chemistry, texture and major elements abundances indicate they were derived and equilibrated under upper mantle conditions within temperature range for 970-1090[degrees]C. Pressure estimates based on the spinal lherzolite stability field restrict the xenoliths source depth to around 65 km. The concentrations of incompatible trace elements (Ba, Rb and Sr.) imply a derivation from ultramafic predictive source from the upper mantle with low degree of melting ( Keywords: Alkali olivine basalt, contamination of the basaltic magma, ultramfic xenoliths, INTRODUCTION The Tertiary-Quaternary basaltic plateau of northeast Jordan is part of the large intra-continental volcanic province of Harrat Al-Shaam, which covers an area of about 45.000 [km.sup.2] and extends continuously [...]

A new thermodynamic model for sodic pyroxenes involving jadeite-diopside-hedenbergite-acmite is presented. This model allows for ordering of Mg, Al, [Fe.sup.2+], and [Fe.sup.3+] on the M1 sites, with coupled Na and Ca ordering on the M2 sites. It is calibrated on the basis of experiments in three chemical subsystems together with available information on ordering in different pyroxenes and on the limited calorimetric data. Central to the determination of the parameters of the model is the use of relationships among the end-member Gibbs energies and the interaction energies in the various possible non-independent sets of end-members. An important aspect of this model, which uses the symmetric formalism, is that Fe-Mg (FM) and Al-[Fe.sup.3+] (AF') mixing is not assumed to be ideal. The model accounts successfully for the experiments at both 600[degrees]C and at higher temperatures involving ordered and disordered pyroxenes coexisting with albite and quartz in NCMAS, NCFAS, NF'AS systems as well as the available calorimetry. It is also able to predict the positions and slopes of tielines in coexisting jadeite + omphacite and omphacite + augite found in nature at lower temperatures. Although the model requires a large number of energy parameters, some of these are not critical to the behavior of the model, while for others the constraints from experiment, calorimetry, ordering state and solvi lead to very limited allowable combinations. The model places some restrictive constraints on the shape of the phase relations in the jadeite-augite-acmite system. Petrological applications of the model are illustrated via a phase diagram example for a MORB bulk composition eclogite. Keywords: Thermodynamics, omphacite, activity-model, eclogite, phase equilibria, metamorphic petrology, mixing properties

The Ti-in-zircon thermometer is a potentially powerful new petrological tool, but conclusions drawn from such data are meaningful only to the extent that the underlying interpretational framework is sound. In the case of interpretation of detrital zircon crystallization temperature spectra, it has been assumed that comparisons can be made with potential host rocks based on calculated bulk zircon saturation thermometry. We show by calculation that most igneous rocks formed at high temperature (>750 [degrees]C) will yield Ti-in-zircon temperatures ([T.sub.Ti.sup.zir]) well above the wet granite solidus. This prediction is borne out by results from the Dala igneous complex, southeastern Tibet, which show a 300 [degrees]C range in [T.sub.Ti.sup.zir] beginning >100 [degrees]C above the calculated bulk zircon saturation temperature. Thus the dominant [T.sub.Ti.sup.zir] peak of >4 Ga zircons at ~680 [degrees]C implies a wet, anatectic magma source rather than an origin in intermediate and mafic magmas. Given that preservation and analytical effects select against, or obscure recognition of, zircons formed at low temperature, the best explanation for the low Hadean [T.sub.Ti.sup.zir] peak is that it reflects derivation from rocks that experienced prograde melting conditions under near-water-saturated conditions. Keywords: zircon, crystallization, saturation, Ti thermometer, tonalite, Jack Hills.

The isotopic compositions of xenoliths hosted in lavas from Floreana Island indicate that they formed from magmas unlike those at present-day Floreana. Instead, the xenoliths are geochemically more similar to magmas now erupting from Sierra Negra and Cerro Azul volcanoes, at the leading edge of the Galapagos hotspot. This is the first evidence for compositional evolution at a Galapagos volcano and indicates increasing contributions from an isotopically enriched source with time as the volcano is carried away from the focus of the hotspot. Clinopyroxenes in many of the xenoliths exhibit positive anomalies of Sr and Eu, which are attributed to the breakdown of plagioclase. The growth of clinopyroxene at the expense of plagioclase results from compression as the crust cools. Compression is caused by growth mostly from above, as shallow intrusions and lavas load the middle and upper oceanic crust. Keywords: xenoliths, underplating, Galapagos Islands, compression, trace elements, igneous petrology.

Incorporation of solid wall rocks is an oft-cited process in the evolution of magmas, but this process is severely limited by the energy required to dissolve xenoliths. Disaggregation without melting has been proposed as an alternative process for incorporating xenoliths into magma because disaggregation avoids expending the energy required for melting. Analysis of these processes using enthalpy-composition diagrams shows that both processes rapidly lead to high crystal contents in the hybrid magma. For example, incorporation of 25% granite at 400 [degrees]C into basalt magma at 1125 [degrees]C produces a hybrid magma at 1050 [degrees]C with >50% crystals; if the granite disaggregates without melting, the crystal content is 65%-70%. Once the crystal content reaches ~50% the viscosity of the magma is too high to allow further magma movement or xenolith incorporation. Thus, both processes are self-limiting and probably restricted in natural systems to at most a few tens of percent incorporation of xenoliths. Keywords: magma, thermodynamics, igneous petrology, assimilation.

To explore the effect of variable C[O.sub.2] concentrations on the solidus of natural carbonated peridotite, we determined near-solidus phase relations of three different nominally anhydrous, carbonated lherzolite bulk compositions at 6.6 GPa. Starting mixes (PERC, PERC2, and PERC3) were prepared by adding variable proportions of a carbonate mixture that has the same Ca:Mg:Fe:Na:K ratio as the base silicate peridotite [MixKLB-1: Mg no. = 89.7; Ca no. = molar Ca/(Ca + Mg + Fe*) = 0.05]. For all three bulk compositions, the subsolidus assemblage includes olivine, orthopyroxene, clinopyroxene, garnet, and magnesite solid solutions. Above the solidus, crystalline carbonate disappears and quenched Fe, Na-bearing dolomitic carbonatite melts were observed. For PERC3 (1.0 wt% bulk C[O.sub.2]; [Na.sub.2]O/C[O.sub.2] weight ratio = 0.30), the observed solidus is between 1190 and 1220 [degrees]C; for PERC (2.5 wt% bulk C[O.sub.2]; [Na.sub.2]O/C[O.sub.2] = 0.12), it is between 1250 and 1275 [degrees]C; and for PERC2 (5.0 wt% bulk C[O.sub.2]; [Na.sub.2]O/C[O.sub.2] = 0.06), it is between 1300 and 1330 [degrees]C. At 6.6 GPa, experimental solidi of natural magnesite peridotites are 100-200 [degrees]C lower than the CMAS-C[O.sub.2] solidus, chiefly owing to the fluxing effect of alkalis, and solidus temperatures increase with increasing bulk C[O.sub.2] (i.e., decreasing bulk [Na.sub.2]O/C[O.sub.2]), owing to dilution of Na20 in near-solidus melt. The effects of Mg no. and Ca no. on carbonated peridotite solidi appear to be less significant than that of [Na.sub.2]O/C[O.sub.2]. Trends of decreasing solidus temperature with increasing [Na.sub.2]O/C[O.sub.2] and with decreasing C[O.sub.2] indicate that natural mantle peridotite with ~100-1000 ppm bulk C[O.sub.2] will have solidus temperatures ~20[degrees] to ~100[degrees] lower than that determined experimentally. The solidus of peridotite drops discontinuously by ~600 [degrees]C (at 6.6 GPa) at the C[O.sub.2] bulk concentration (~5 ppm) at which carbonate is stabilized, but then varies little with increasing bulk C[O.sub.2]. This result contrasts with the effect of [H.sub.2]O, which lowers the solidus continuously with increasing concentration. Keywords: Carbonated peridotite, carbonatite, mantle solidus, experimental petrology, partial melting