内蒙古野芨里镁铁质——超镁铁质岩体的岩石地球化学特征

野芨里岩体分布于金川铜镍(铂)硫化物矿床北偏东约100 km处,位于内蒙古境内。岩体主要由单斜辉石橄榄岩、二辉橄榄岩、辉长岩和闪长岩组成。岩体的稀土元素配分模式显示轻稀土元素略为富集,曲线为近于平坦型,w(La)_N/w(Yb)_N=1.866～2.713,不具备会聚型板块边缘玄武岩的特点;ε_Nd(t)＞0,为亏损地幔源区特征。Mg^#值和Ni丰度显示其为岩浆早期阶段堆晶作用的产物。与金川矿区超镁铁质岩体比较,二者均为华北大陆边缘成矿系统的组成部分,m/f值显示二者主要为铁质超基性岩,稀土元素及微量元素显示其具相似的地球化学特征,但野芨里岩体具早期堆晶就地熔离的特征,而金川岩体具有深部熔离-多期贯入的特征;野芨里岩体中Ni相对亏损。这些特征表明野芨里岩体具成矿的可能性。     

Petrological, Geochemical and Isotopic Constraints on the Origin of the Harzburg Intrusion, Germany

We present mineralogical, petrological and geochemical datato constrain the origin of the Harzburg mafic–ultramaficintrusion. The intrusion is composed mainly of mafic rocks rangingfrom gabbronorite to quartz diorite. Ultramafic rocks are veryrare in surface outcrops. Dunite is observed only in deepersections of the Flora I drill core. Microgranitic (fine-grainedquartz-feldspathic) veins found in the mafic and ultramaficrocks result from contamination of the ultramafic magmas bycrustal melts. In ultramafic and mafic compositions cumulatetextures are widespread and filter pressing phenomena are obvious.The order of crystallization is olivine pargasite, phlogopite,spinel plagioclase, orthopyroxene plagioclase, clinopyroxene.Hydrous minerals such as phlogopite and pargasite are essentialconstituents of the ultramafic cumulates. The most primitiveolivine composition is Fo_89·5 with 0·4 wt % NiO,which indicates that the olivine may have been in equilibriumwith primitive mantle melts. Coexisting melt compositions estimatedfrom this olivine have mg-number = 71. The chemical varietyof the rocks constituting the intrusion and the mg-number ofthe most primitive melt allow an estimation of the approximatecomposition of the mantle-derived primary magma. The geochemicalcharacteristics of the estimated magma are similar to thoseof an island-arc tholeiite, characterized by low TiO₂ and alkalisand high Al₂O₃. Geochemical and Pb, Sr and Nd isotope data demonstratethat even the most primitive rocks have assimilated crustalmaterial. The decoupling of Sr from Nd in some samples demonstratesthe influence of a fluid that transported radiogenic Sr. Leadof crustal origin from two isotopically distinct reservoirsdominates the Pb of all samples. The ultramafic rocks and thecumulates best reflect the initial isotopic and geochemicalsignature of the parent magma. Magma that crystallized in theupper part of the chamber was more strongly affected by assimilatedmaterial. Petrographic, geochemical and isotope evidence demonstratesthat during a late stage of crystallization, hybrid rocks formedthrough the mechanical mixing of early cumulates and melts withstrong crustal contamination from the upper levels of the magmachamber. KEY WORDS: Harzburg mafic–ultramafic intrusion; Sr–Nd–Pb isotopes; magma evolution; crustal contamination     

豫西花山花岗岩基岩石学和地球化学特征及其成因

花山花岗岩岩基是燕山期在华北地台南缘发生的陆内挤压俯冲作用的产物。组成该岩基的万村、蒿坪和金山庙岩体的矿物学、岩石化学、稀土及微量元素地球化学特征均可以与Ⅰ型（或华南同熔型）花岗岩相类比，反映出该地壳重熔成因的花岗岩对源岩──变质的中基性火山岩（太华群）的继承作用。因此，在划分花岗岩类的成因类型时，应考虑到其形成的地质背景、源岩性质及成岩方式等因素。     

Petrological, Geochemical and the Origin of the Cuobuzha Peridotite in the Western Yarlung Zangbo Suture Zone

<正>Ophiolites are fragments of ancient oceanic lithosphere emplaced onto continental margins,accretionary prisms,or island arcs during plate collisions(Dilek and Furnes,2011).The well-preserved ophiolitic sequence provides important information on melt extraction,melting,and melt-rock interaction in the upper mantle of paleo-oceanic     

河北省丰宁县大草坪钼矿区花岗质岩石地球化学特征及地质意义

大草坪钼矿区侵入体由花岗岩和花岗闪长岩组成,两者呈侵入接触关系,接触带附近石英脉较发育并见钼矿化。花岗岩与花岗闪长岩具有相似的岩石地球化学特征:主量元素特征均显示富含硅、碱质,普遍具有较高的钾含量,主要属钙碱性系列;稀土元素球粒陨石标准化配分模式显示LREE相对富集,球粒陨石标准化曲线都一致向右倾斜,曲线之间呈现近于平行的特征,说明两者具有同源性。笔者同时认为,大草坪岩体的成因类型为I型花岗岩,岩浆物质具壳幔混源特征;岩体与矿体具有明显的同源分异特征,可为成矿提供一定物质来源。     

Magma Mixing Origin of Yamatu Granite in Nuoergong-Langshan Area,Western Part of the Northern Margin of North China Craton:Petrological and Geochemical Evidences

华北地块北缘西段巴音诺尔公—狼山地区的牙马图岩体以二长花岗岩为主,岩体中广泛发育岩浆暗色包体,二者界线明显.包体为岩浆结构,大多数具有塑性外形,发育淬冷边、反向脉,存在多种不平衡结构和矿物组合,如斜长石环带、石英眼斑、针状磷灰石等,显示岩浆混合特征;包体的SiO2含量为48.40％～55.40％,寄主花岗岩SiO2含量为65.03％～72.85％,具有明显的SiO2含量间隔;与寄主花岗岩相比,包体的Fe、Mg、Ca、Ti含量较高;包体和寄主花岗岩的主要氧化物之间具有很好的线性关系,微量元素和稀土元素特征相似.包体和寄主花岗岩的这些地球化学特征显示出明显的岩浆混合趋势.岩相学和元素地球化学特征表明暗色包体是基性岩浆侵入到酸性岩浆淬冷的产物,牙马图岩体存在两种岩浆的混合作用.     

Indosinian Tectonic Transition in Yunkai Massif: Petrological and Geochemical Constraints from Two-mica Granite in Yangchun Area,South China

The tectonic background of the Indosinian granites in South China Block remains highly debated. The Yunkai massif, connecting the Paleo-Tethys and Paleo-Pacific tectonic domains, is a key site for studying the tectonic background of the Indosinian granitoids in South China. In this paper, we select a two-mica granitic pluton from the Yangchun area of the Yunkai Massif to conduct comprehensive researches including petrology, geochronology, and geochemistry. Zircon U-Pb dating yield two concordant 206Pb/238U ages of 426.4±1.7 Ma (MSWD=2.4, n=8) and 239.1±1.7 Ma (MSWD=1.2, n=4), respectively. A further monazite U-Pb dating gives only one concordant 206Pb/238U age at 239.0±0.3 Ma (MSWD=1.2, n=31), consistent with the younger zircon U-Pb age. We therefore conclude that the Yangchun two-mica granite was formed during Triassic (ca. 239 Ma). The granite rocks belong to S-type granite with a peraluminous affinity. They also show enrichment in large ion lithophile elements and depletion in high field strength elements and relatively flat chondrite-normalized rare earth element patterns with negative Eu anomalies, and have low zircon saturation temperature of 725–747 ℃ as well. The bulk-rock and monazite Nd and zircon Hf isotope analyses yield whole-rock εNd(t) values from –10.8 to –9.4, monazite εNd(t) values from –10.9 to –8.4, and zircon εHf(t) values from –13.2 to –7.8, with depleted model age ranges of 1.8–1.9 Ga for whole rock tDM2(Nd), 1.7–1.9 Ga for monazite tDM2(Nd) and 1.8–2.1 Ga for zircon tDM2(Hf). The consistent Nd and Hf isotope data among the bulk rock, monazite and zircon in the Yangchun two mica granite indicate that the granite was derived from ancient recycled crustal components. The parent magma experienced a dominated fractionation of plagioclase and monazite which resulted in the negative Sr and Eu anomalies and low LREE concentrations. Considering the regional geological background, we propose that the two-mica granite in the Yangchun area formed during the tectonic transition between the oceanic slab subduction and orogenic collapse: The late Permian shallow-marine sedimentary sequences and I-type granitic magmatism indicate the subduction of Paleo- Tethys Ocean; the early-middle Triassic crustal shortening and thickening triggered the crustal anatexis to form the S-type granitic magmas such as the Yangchun two-mica granitic pluton; the late Triassic terrestrial red deposits and the occurrence of A2-type granite suggest a stage of orogenic collapse and the resultant lithospheric extension. © 2023 Science Press. All rights reserved.     

湖南千里山花岗岩的岩石学和地球化学研究

本文从岩石学、岩石化学等方面详细研究了湘南东坡矿田内的花岗岩体,认为岩体分四次侵入就位。前三次侵入岩体在岩体的产状、岩石的矿物成分、化学成分及稀土元素和其他微量元素的分配上都具有明显的相同演化趋势,表明它们是同源岩浆分离结晶作用的产物,而第四次侵入岩体则不符合这一演化趋势,表明与前三者不是同源岩浆产物,根据其产状特征,可能来自更深的位置。不同期次的侵入体,具有不同的矿化特征,从而构成本矿田特有的成矿模式。     

安徽月山岩体地球化学特征及成因机理分析

通过对长江中下游地区具代表性的大型矽卜岩－热液脉型铜（铁）、金、多金属矿田中成矿岩体－月山岩体的地质地球化学特征及其成因制约与反演讨论，认为该岩体为深源的碱性玄武质岩浆经过结晶分异和同化混染联合作用（AFC过程）形成的，其中，幔源物质约占70％，同化的壳源物质占30％。这种开放岩浆系统的形成与演化对于该区金属矿床成矿流体系统的形成与演化具有极其重要的意义。     

Magnetic susceptibility mapping of felsic magmatic lithounits in the central part of Bundelkhand Massif,central India

Late Archaean to Palaeoproterozoic felsic magmatic lithounits exposed in the central part of the Bundelkhand massif have been mapped and their redox series (magnetite vs ilmenite series) evaluated based on magnetic susceptibility (MS) data. The central part of Bundelkhand massif comprises of multiple felsic magmatic pulses (∼2600–2200 Ma), commonly represented by coarse grained granite (CGG-grey granite, CPG-pink granite), medium grained pink granite (MPG), fine grained pink granite (FPG), grey and pink rhyolites and granite porphyry (GP). However, the pink colour of these felsic rocks is the result of hydrothermal fluid-flushing leading to potassic alteration of grey granites. MS values of CGG vary from 0.058 to 14.75×10⁻³ SI with an average of 6.35×10⁻³ SI, which mostly represent oxidized type, magnetite series (73%) granites involving infracrustal (igneous) source materials. CPG (av. MS=3.95×10⁻³ SI) is indeed a pink variety of CGG, the original oxidizing nature of which must have been similar to the bulk of CGG, but has been moderately to strongly reduced because of distinctly more porphyritic nature together with partial assimilation of metapelitic (supracrustal) materials, surmicaceous enclaves, carbonaceous material included in the source materials, and to some extent, induced by hydrothermal and later deformational processes. MPG (av. MS= 1.15×10⁻³ SI) as lensoidal stock-like bodies intrudes the CPG and represent both magnetite series (18%) and ilmenite series (82%) granites, which are probably formed by heterogeneous (mixed) source rocks. GP (av. MS=6.26×10⁻³ SI) occur as dykes (mostly trending NE-SW) intrudes the MPG, CPG and migmatites and bears the nature similar to oxidized type, magnetite series granite. FPG (av. MS= 0.666×10⁻³ SI) trending NE-SW occur as lensoid bodies including a large outcrop, is intrusive into both CPG and MPG, and is moderately to very strongly reduced type, ilmenite series granites, which may be derived by the melting of metapelitic crustal sources. FPG hosting microgranular (mafic magmatic) enclaves commonly exhibit high MS values (7.31–10.22×10⁻³ SI), which appear induced by the mixing and mingling of interacting felsic and mafic magmas prevailed in an open system. Grey (av. MS=10.30×10⁻³ SI) and pink (av. MS=6.72×10⁻³ SI) rhyolites represent oxidized type, magnetite series granites, which may have been derived from infracrustal (magmatic) protoliths. Granite series evaluation of felsic magmatic rocks of central part of Bundelkhand massif strongly suggests their varied redox conditions (differential oxygen fugacity) mostly intrinsic to magma source regions and partially modified by hydrothermal and tectonic processes acting upon them.     

Petrological evidences of impact-induced shock metamorphism in the basement granitoids and rhyolitic melt breccia of Mohar area,Shivpuri district,Madhya Pradesh

The circular structure at Mohar (Dhala structure) in the western part of Bundelkhand Gneissic Complex, is marked by a prominent outlier of Kaimur sediments surrounded by low lying concentric sequence of sediments of Dhala Formation and basement granite breccia. This has been interpreted as a volcanic eruption related cauldron structure and meteoritic impact crater structure by various authors, on the basis of absence or presence of shock indicators in the clasts of a rhyolite-like rock that crops out scantily in the north western part of the structure. During the course of extensive sub-surface uranium exploration in this structure, the geoscientists of Atomic Minerals Directorate for Exploration and Research observed unequivocal and rampant evidences of shock metamorphic features for the first time in drill core samples of basement granitoids which constitute the bed rock for the rhyolite-like melt breccia, which overlies it. Published data of shock metamorphic features from this area are largely confined to the surface samples of the rhyolite-like melt rock, exposed in sparse outcrops. The shock metamorphic features recorded in the sub-surface granitoid bed rock samples during the present study, comprise planar deformation features (PDF) in quartz, feldspar, apatite and zircon, toasted, diaplectic, ladder-textured feldspars, selectively shock-melted feldspars and melt-veined quartz. The shock metamorphic features recorded in surface and sub-surface samples of the melt rock include ballen quartz, PDF in quartz clasts, toasted and diaplectic feldspar clasts shocked basic rock fragments with isotropised feldspars. Both the shocked bedrock granitoid and the melt rock bear uncharacteristic geochemical signatures with elevated K₂O, MgO and depleted CaO. The study also observes that the melt breccia overlying the granitoid bedrock also occurs as pocket-like patches at various depths within the granitoids. Thus, the present findings have helped in understanding the attributes of the basement granitoid and associated melt breccia, thereby linking the genesis of the latter by selective melting of the former, due to the process of impact. It reinforces the already propounded theory of impact as the likely cause for the development of the structure in the basement Bundelkhand granitoid that was later filled by sediments standing out presently as a mesa.     

Potassic Magmatism in Western Sichuan and Yunnan Provinces, SE Tibet, China: Petrological and Geochemical Constraints on Petrogenesis

Potassic volcanism in the western Sichuan and Yunnan Provinces,SE Tibet, forms part of an extensive magmatic province in theeastern Indo-Asian collision zone during the Paleogene (40–24Ma). The dominant rock types are phlogopite-, clinopyroxene-and olivine-phyric calc-alkaline (shoshonitic) lamprophyres.They are relatively depleted in Na₂O, Fe₂O₃, and Al₂O₃ comparedwith the late Permian–early Triassic Emeishan continentalflood basalts in the western part of the Yangtze craton, andhave very high and variable abundances of incompatible traceelements. Primitive mantle-normalized incompatible element patternshave marked negative Nb, Ta and Ti anomalies similar to thoseof K-rich subduction-related magmas, although the geodynamicsetting is clearly post-collisional. Spatially, some incompatibletrace element abundances, together with inferred depths of meltsegregation based on the Mg-15 normalized compositions of thesamples, display progressive zonation trends from SW to NE withincreasing distance from the western boundary of the Yangtzecraton. Systematic variations in major and trace element abundancesand Sr–Nd–Pb isotope compositions appear to havepetrogenetic significance. The systematic increases in incompatibletrace element abundances from the western margin to the interiorof the Yangtze craton can be explained by progressively decreasingextents of partial melting, whereas steady changes in some incompatibletrace element ratios can be attributed to changes in the amountof subduction-derived fluid added to the lithospheric mantleof the Yangtze craton. The mantle source region of the lamprophyresis considered to be a relatively refractory phlogopite-bearingspinel peridotite, heterogeneously enriched by fluids derivedfrom earlier phases of late Proterozoic and Palaeozoic subductionbeneath the western part of the Yangtze craton. Calculationsbased on a non-modal batch melting model show that the degreeof partial melting ranges from 0·6% to 15% and the proportionof subduction-derived fluid added from0·1% to 0·7%(higher-Ba fluid) or from 5% to 25% (lower-Ba fluid) from theinterior to the western margin of the Yangtze craton. Some pre-existinglithospheric faults might have been reactivated in the areaneighbouring the Ailao Shan–Red River (ASRR) strike-slipbelt, accompanying collision-induced extrusion of the Indo-Chinablock and left-lateral strike-slip along the ASRR shear zone.This, in turn, could have triggered decompression melting ofthe previously enriched mantle lithosphere, resulting in calc-alkalinelamprophyric magmatism in the western part of the Yangtze craton. KEY WORDS: Tibet; potassic magmatism; lithospheric mantle; metasomatism     

Geochemical and Isotopic Geochemical Characteristics of PGE Mineralization in the Lukkulaisvaara Layered Massif,Karelia, Russia

The study of the Lukkulaisvaara layered massif from the Olang group of intrusions in northern Karelia corroborates the important role of supplementary intrusive phases of PGE mineralization. Injection and crystallization of new magma portions result in (1) the formation of potholelike depressions within intrusion and (2) a return to high-temperature olivine-bearing mineral assemblages in the mafic part of section. PGM formation is accompanied by crystallization of secondary minerals in a wide range of temperatures and pressures. To provide insight into these problems, a geochemical study of Nadezhda area has been performed and new data obtained for the distribution of isotopes in the Rb–Sr, Pb–Pb, and Sm–Nd systems.     

Geochemical specifics of ongonites in the Ary-Bulak Massif, eastern Transbaikalia

A genetic model for magmatic rocks of the Ary-Bulak Massif is discussed based on a detailed geological map of the massif (prepared by the authors) and on original data of the authors on the petrography of the massif, its compositional zoning, trace-element geochemistry, physicochemical parameters of its crystallization, and melt inclusions in its minerals. The Ary-Bulak Massif was determined to be zonal, with the predominance (approximately 70% by area) of porphyritic topaz ongonites (central facies), which grade toward contacts into weakly porphyritic ongonites bearing topaz and, occasionally, fluorite (margin facies). Aphyric rocks with fluorite (inner-contact facies) occur as a stripe 50–80 m wide at the southwestern inner contact of the massif. Analysis of petrographic and geochemical data indicates that subvolcanic rocks of the Ary-Bulak Massif differ from typical elvanes (as they occur in the Cornwall province) but are similar to classic ongonites in the central and marginal facies of the massif. Rocks in the southwestern inner-contact zone are unusual high-F and high-Ca varieties, whose analogues have never been found in any rare-metal provinces with ongonites and which provide evidence of a complicated evolutionary history of the Ary-Bulak Massif. The geochemical evolution of this massif was determined to be characterized by the enrichment of the older inner-contact facies rocks in CaO, K₂O, F, and Rb, Cs, B, Ba, Sr, Sn, and Ta, whose concentrations decrease in the ongonites of the central facies. The central-facies ongonites thereby have much higher Na₂O and Li concentrations than those in the inner-contact facies rocks. It is demonstrated that the intense heating and melting of crustal material in this region at the Jurassic-Cretaceous boundary could have been induced by subalkaline basaltic magma. The chemical composition of the rocks, which is unusual for typical ongonites in, for example, high Ca and Sr concentrations, could be caused by the possible assimilation by the magma of limestones, which occur in the territory at a certain depth in the Ust’-Borzya Formation that hosts the Ary-Bulak Massif. The genesis of most rocks in the massif was controlled by the magmatic differentiation of crustal granitic magma, with the residual melts forming Li-F granites enriched in several trace elements (Li, Rb, Cs, B, Ba, Sr, etc.) and ongonites as their subvolcanic analogues.     

A Study of Macro-Rhythmic Layering and Cumulate Processes in the Jimberlana Intrusion, Western Australia. Part I: The Upper Layered Series

The upper layered series of the Jimberlana Intrusion rests unconformablyon the lower layered series and has resulted from a major newpulse of magma which entered the magma chamber during the finalstages of crystallization of the lower series. All parameterswhich vary systematically with fractionation are sharply reversedat the contact between the two layered series. The lower portion of the ultramafic zone of the upper layeredseries is composed of a repeated macro-rhythmic succession ofolivine cumulates, bronzite-olivine cumulates, and bronzitecumulates. A detailed investigation was made of this sequenceso that the contacts between the units could be compared withthe contact between the upper and lower layered series. Cu,Ni, Cr, P, and U were measured on a whole rock basis; the Mg/Mg?Feratios of the pyroxenes and olivines, the Cr content of pyroxenesand the Ni content of olivines were determined by the electronmicroprobe. Each of the macro-rhythmic units is associated witha reversal in mineral variation and in the Ni-Cr trends andhas a zone of high sulphide values at its base. These featuresare also found at the contact between the upper and lower layeredseries and, if the upper series is due to a new influx of magma,it follows that the macro-units are also due to multiple injection.This conclusion is strongly supported by the size of the reversalswhich are too large to be explained by the alternative hypothesesto multiple injection suggested by Jackson (1961) and Wager(1959). The anomalous sulphide-rich zones at the contacts between theupper and lower layered series and between the macro-rhythmicunits are thought to have formed from a narrow supercooled zonewhich developed for a brief period at the bottom of the magmachamber following each new magma pulse. The olivines from thesesulphide-rich zones are depleted in Ni, suggesting that Ni hasbeen scavenged by the sulphides. This is only possible if theolivine grains crystallized with the sulphides in the restrictedsupercooled zone at the bottom of the magma chamber.     

大兴安岭中南段中生代中基性火山岩岩石学地球化学研究

大兴安岭中南段中生代火山岩的成因和形成时的构造背景涉及南蒙古-兴蒙造山带的后期构造演化及区内众多的铜、银多金属矿床的形成,因而对其成因的研究具有重要意义。在野外工作基础上,对大兴安岭中南段中生代中基性火山岩进行了较为系统的岩石学和元素地球化学研究。结果表明,火山岩的岩石类型为玄武粗安岩、粗面安山岩、英安岩及粗面岩,属钙碱性岩石系列;玄武粗安岩、粗面安山岩、英安岩及粗面岩的常量元素以富集SiO2,Na2O,K2O和亏损Fe2O3,FeO,MgO,CaO等为特征,微量元素以富集亲石元素和亏损铁族元素及Nb,Ta为特征;火山岩的稀土元素分配模式为轻稀土富集型;(^87Sr／^86Sr)．为0．7045～0．7077,且主要集中在0．7045～0．7055的区间内,εNd(t)多数为正值。火山岩是地幔物质部分熔融的产物,形成于张性构造环境,它们是天山一兴安造山带后造山期软流圈或地幔柱上涌所引起的岩石圈伸展作用、内蒙古-吉黑印支造山带造山期后的伸展作用和蒙古-鄂霍茨克残余洋“剪刀式”闭合所形成的拉张作用等综合效应的响应事件。     

Multi-stage Garnet in the Internal Brianconnais Basement (Ambin Massif, Savoy): New Petrological Constraints on the Blueschist-facies Metamorphism in the Western Alps and Tectonic Implications

Three types of garnet have been distinguished in pelitic schistsfrom an epidote–blueschist-facies unit of the Ambin andSouth Vanoise Briançonnais massifs on the basis of texture,chemical zoning and mineral inclusion characterization. Type-1garnet cores with high Mn/Ca ratios are interpreted as pre-Alpinerelicts, whereas Type-1 garnet rims, Type-2 inclusion-rich porphyroblastsand smaller Type-3 garnets are Alpine. The latter are all characterizedby low Mn/Ca ratios and a coexisting mineral assemblage of blueamphibole, high-Si phengite, epidote and quartz. Prograde growthconditions during Alpine D₁ high-pressure (HP) metamorphismare recorded by a decrease in Mn and increase in Fe (±Ca)in the Type-2 garnets, culminating in peak P–T conditionsof 14–16 kbar and 500°C in the deepest parts of theAmbin dome. The multistage growth history of Type-1 garnetsindicates a polymetamorphic history for the Ambin and SouthVanoise massifs; unfortunately, no age constraints are available.The new metamorphic constraints on the Alpine event in the massifsdefine a metamorphic T ‘gap’ between them and theirsurrounding cover (Briançonnais and upper Schistes Lustrésunits), which experienced metamorphism only in the stabilityfield of carpholite–lawsonite (T < 400°C). Thesedata and supporting structural studies confirm that the Ambinand South Vanoise massifs are slices of ‘eclogitized’continental crust tectonically extruded within the SchistesLustrés units and Briançonnais covers. The correspondingtectonic contacts with top-to-east movement are responsiblefor the juxtaposition of lower-grade metamorphic units on theAmbin and South Vanoise massifs. KEY WORDS: Alpine HP metamorphism; Ambin and South Vanoise Briançonnais basements; metamorphic gaps; multistage garnets; Western Alps     

Mineralogical and Petrological Characteristics of the Neoproterozoic Orthoamphibolite and Orthogneisses in the Mutki Area, the Bitlis Massif, Southeast Turkey

<正>The rocks form as amphibolite±garnet±epidote and orthogneisses in the Pan-African basement of the Bitlis Massif.The petrochemical data of the studied metamorphic rocks suggest different igneous protoliths ranging from calcalkaline basalt to andesite in composition. Petrochemically,the rocks can be classified as group 1(low Zr and La) and group 2(high Zr and La), all showing various enrichments in large ion lithophiles and light rare earth elements,and a depletion in high-field strength elements,suggestive of a destructive plate margin setting.The protoliths of the all samples might have formed mostly by the partial melting of an enriched source,possibly coupled with the fractional crystallization of plagioclase,apatite,and titaniferous magnetite±olivine±clinopyroxene±amphibole in relation with subduction-related magmatism neighboring the Andeantype active margins of Gondwana.The group 2 samples could,however,be generated by a relatively lower degree of the partial melting of an inhomogeneous source with a preponderance of a high-level, fractional crystallization process in comparison to group 1.The protoliths of the samples were metamorphosed up to amphibolite facies conditions,which destroys original igneous texture and mineral assemblages.Geothermobarometric calculations show that the metamorphic rocks are finally equilibrated between 540 and 610℃and～5 kbars,following a clockwise P-T-t path.