Zr-in-rutile thermometry of eclogites from the Karakaya Complex in NW Turkey: Implications for rutile growth during subduction zone metamorphism

Eclogites occur as a tectonic slice within a metabasite-phyllite-marble unit of the Karakaya Complex in northwest Turkey. The high-pressure mineral assemblage in eclogite is mainly composed of garnet + omphacite + glaucophane + epidote + quartz. Trace element characteristics of rutile and Zr-in-rutile temperatures were determined for eclogites from the Karakaya Complex. Core-rim analyses of rutile grains yield remarkable trace element zoning with lower contents of Zr, Nb and Ta in the core than in the rim. The variations in Zr, Nb and Ta can be ascribed to growth zoning rather than diffusion effects. The Nb/Ta and Zr/Hf ratios increase with a decrease in Ta and Hf contents, which could be ascribed to the effect of metamorphic dehydration in subduction zones on rutile Nb/Ta differentiation. The rutile grains from eclogites in the Karakaya Complex are dominated by subchondritic Nb/Ta and Zr/Hf ratios. It can be noted that subchondritic Nb/Ta may record rutile growth from local sinks of aqueous fluids from metamorphic dehydration.The Zr contents of all rutile grains range between 81 and 160 ppm with an average of 123 ppm. The Zr-in-rutile thermometry yields temperatures of 559–604 °C with an average temperature of 585 °C for eclogites from the Karakaya Complex. This average temperature suggests growth temperature of rutile before peak pressure during the subduction. However, some rutile grains have higher Zr contents in the outermost rims compared to the core. Zr-in-rutile temperatures of the rims are about 20 °C higher than those of the cores. This suggests that the outermost rims would have grown from a distinct fluid at higher temperatures than that of the cores. Moreover, Zr contents and calculated temperatures in both inclusion rutile and matrix rutile from eclogites are identical, which suggests that eclogites within the Karakaya Complex belong to the same tectonic slice and underwent similar metamorphic evolution.     

塔里木盆地库鲁克塔格地区二叠纪末-中三叠世基性岩床的发现及其地质意义

新疆塔里木盆地东北缘库鲁克塔格地区的中寒武统莫合尔山组沉积地层中发现三条形成于二叠纪末到中三叠世的基性岩床。三条岩床沿沉积岩层面顺层侵入,按照从下到上的顺序,分别为辉绿岩床(厚3m)、辉长岩床(厚20m)和粗玄岩床(厚2.5m)。三条岩床的地球化学特征相似,稀土含量高(∑REE=210×10^-6~297×10^-6),轻稀土元素富集((La/Yb)_N =13.54~17.96),Eu负异常不明显(δEu=0.97~1.21),Ce稍具正异常(δCe=1.11~1.25)。大离子亲石元素(Rb、Ba、Th、Sr)富集,Sr具明显正异常; Ta、Nb和Hf具负异常。低氧化度(0.13~0.40)。三条岩床为同源岩浆活动的产物,岩浆源于上地幔或下地壳,但有下陆壳成分混染。三个样品的MgO含量在4%~6%之间,Mg^#值在37.6~55.6之间,固结指数SI值位于18.7~29.3之间,反映原始的岩浆经历了比较明显的分异作用。粗玄岩床K-Ar年龄为255.2±7.3Ma,辉绿岩床K-Ar年龄为242.8±5.7Ma,辉长岩床Ar-Ar年龄为229.7±3.7Ma。本次岩浆侵入事件发生在南天山洋闭合之后,构造背景为造山后碰撞伸展环境。     

重庆长河碥矿煤的微量元素地球化学特征

运用煤岩学和地球化学的理论和方法,对重庆长河碥矿晚三叠世须家河组煤中微量元素进行了研究。结果表明,长河碥矿各煤层中明显富集Pb,其平均值为29.58μg/g。长河碥矿煤中潜在的有害微量元素Be (5.9μg/g)、Cr (28.6μg/g)、Cu (34.06μg/g)、As (10.03μg/g)和Th (12.49μg/g)均较富集;稀土元素含量为59.79²87μg/g,均值为136.92μg/g,略高于中国煤中稀土元素总量均值(119.7μg/g),高于美国煤中的稀土元素总量均值(53.59μg/g)。8煤中稀土元素含量异常可能是地下水淋滤作用的结果。长河碥矿煤中有害微量元素主要受控于陆源物质的供给。     

云南鲁春晚三叠世硅质岩的地球化学特征及成因

云南鲁春晚三叠世火山沉积盆地是在江达-维西火山弧的基础之上,通过拉张作用形成的碰撞后拉张盆地,盆地内广泛发育一套由玄武岩和流纹岩组成的“双峰式”火山岩及与其相伴的硅质岩。硅质岩可分为凝灰质硅质岩和纹层状硅质岩两类。通过对两类硅质岩所进行的地球化学研究和分析,表明云南鲁春晚三叠世火山沉积盆地中的凝灰质硅质岩属火山沉积成因,而纹层状硅质岩为海底喷流热液/热泉(热水)沉积成因的热水硅质岩。     

Low-grade metamorphic rocks from the Pulur complex,NE Turkey: implications for the pre-Liassic evolution of the Eastern Pontides

In the Pulur complex (Sakarya Zone, Eastern Pontides, Turkey) a low-grade tectonometamorphic unit (Doankavak) is exposed in three tectonic windows beneath a complex medium-pressure high-temperature metamorphic unit of late Carboniferous age. The thrust plane between both units is transgressively covered by Liassic conglomerates. The Doankavak unit comprises a sequence of metabasites with MORB-type chemical compositions and phyllites, with subordinate calcareous phyllites, marbles, quarzofeldspathic schists and metacherts. This sequence is interpreted as a former accretionary complex related to the consumption of the Palaeotethys. Mineral parageneses in the metabasites allow for the distinction of two domains with slightly different peak metamorphic conditions, i.e. 375–425 °C/0.5–0.8 GPa (greenschist facies) and 400–470 °C/0.6–1.1 GPa (albite-epidote amphibolite facies). The age of metamorphism is constrained at ~ 260 Ma (early Late Permian) by two Rb-Sr mineral-whole rock ages (hornblende, phengite) and one ⁴⁰Ar/³⁹Ar single step total fusion age (phengite). In conjunction with previous data on other accretionary complexes in the Sakarya zone in Northern Turkey, the data presented in this study suggest a continuous subduction of the Palaeotethys at least from Early/Late Permian to Late Triassic and a discontinuous preservation of accretion complexes in both space and time.     

右江盆地中三叠世碎屑岩地球化学特征及其物源分析∶以贵州册亨地区为例

右江盆地中三叠世充填了一套巨厚的复理石沉积,岩性为细砂岩、粉砂岩、泥岩及其过渡岩石,其独特的沉积特征颇受国内外地质学界关注,但目前对该套碎屑岩的物源尚有争议。文章通过对册亨地区中三叠世碎屑岩开展详细的岩石学和地球化学分析,结果显示：碎屑岩成分成熟度与结构成熟度都较低,具近源沉积特征。SiO₂（平均为58.49%）含量较低,变化范围较大,说明石英含量较低;Al₂O₃（平均为12.46%）含量较高,说明粘土矿物及长石含量较高;Al₂O₃/SiO₂的比值平均为0.22,与杂砂岩（0.20~0.23）一致,说明碎屑岩成熟度较差,亦具近源沉积特征;CaO（平均为7.83%）含量较高,说明含碳酸盐类物质较多。微量元素表现为富集Rb、Th、La、Nd、Hf和Pb以及相对亏损P、Ti、Sr、Nb和Ta的特点,稀土元素具有ΣREE变化范围大,轻稀土富集,Eu亏损的特点。主量、微量和稀土元素分析表明,碎屑岩的源岩以长英质岩石为主,并有少量中性岩及石英质沉积岩的混入;源区构造背景以大陆岛弧为主,兼有被动大陆边缘及活动大陆边缘特 征。化学蚀变指数（CIA）值为53.93~74.80,均值为65.12。通过CIA以及Th/U比值,表明碎屑岩源区主要经历了中等化学风化作用。     

Petrological evolution of the Middle Triassic Predazzo Intrusive Complex,Italian Alps

The Predazzo Intrusive Complex (PIC), a Ladinian plutonic body located in the Southern Alps (NE Italy), is made up of a 4.5 km³ gabbroic to syenitic and syenogranitic intrusion, basaltic to latitic volcanic products (about 6 km³ in volume) and by an extended dike swarm intruding both intrusive and volcanic rocks. An extensive field survey of the complex, followed by detailed petrographic and geochemical analyses, allowed the identification of three different magmatic units: a Shoshonitic Silica Saturated Unit (SS), 3.1 km³ in volume, a Shoshonitic Silica Undersaturated Unit (SU), 0.3 km³ in volume, and a Granitic Unit (GU), 1.1 km³ in volume. K-affinity, marked Nb and Ti negative anomalies and a strong Pb enrichment are distinctive markers for all PIC lithotypes. A general HFSE (Th, U, Pb), LREE (La, Ce, Pr, Nd) and Na enrichment characterizes the SU suite with respect to the SS series. Mass balance calculations, based on major and trace element whole rock and mineral compositions, have been used to simulate the fractionation process of SS and SU suites, showing (i) the complexity of the evolutionary stages of the PIC and (ii) the analogy between the calculated subtracted solid assemblages and the natural cumulitic lithotypes outcropping in the area. The field relationships between the various portions of the intrusive complex, the volcanic products and the dike swarm define the temporal evolution of the PIC, in which the SS magma batch was followed by the GU and later on by the SU intrusion. The presence, in both eastern and western portions of the complex, of a transitional magmatic contact between the intrusive rocks of the SS suite and the volcanics is not in favour of the hypothesis of a caldera collapse to explain the ring-like shape of the PIC.     

Geochemistry of Cretaceous mafic rocks from the Lower Yangtze region, eastern China: Characteristics and evolution of the lithospheric mantle

Geochemical and isotopic data for Cretaceous mafic rocks (basalt, gabbro, and diorite) from the Lower Yangtze region, northern Yangtze block, constrain the evolution of the lithospheric mantle. The mafic rocks, separated into the northeast and southwest groups, are alkaline and evolved, with low Mg# values (44–58) and variable SiO₂ contents (47.6–57.4 wt%). Enriched LREEs, LILEs, and Pb, together with depleted Nb, Zr, and Ti, suggest that the mantle sources were metasomatized by slab-derived fluid/melt. All samples show high radiogenic ²⁰⁷Pb/²⁰⁴Pb(t) (15.41–15.65) and ²⁰⁸Pb/²⁰⁴Pb(t) (37.66–38.51) ratios at given ²⁰⁶Pb/²⁰⁴Pb(t) (17.65–19.00) ratios, consistent with the mantle sources having been metasomatized by ancient slab-derived material. Mafic rocks of the southwest group show enriched Sr–Nd isotopic characteristics, with ⁸⁷Sr/⁸⁶Sr(t) ranging from 0.7056 to 0.7071 and ε_Nd(t) ranging from −5.3 to −8.3, indicating an origin from enriched lithospheric mantle. Mafic rocks of the northeast group, which record ⁸⁷Sr/⁸⁶Sr(t) ratios of between 0.7044 and 0.7050 and ε_Nd(t) of −2.8 to −0.7, possibly formed by the mixing of melts from isotopically enriched lithospheric mantle and isotopically depleted asthenospheric mantle. Taking into consideration the geochemical and isotopic characteristics of Cretaceous mafic rocks, Cenozoic basalts, and basalt-hosted peridotite xenoliths from the Lower Yangtze region, we propose that an isotopically enriched, subduction-modified lithospheric mantle was replaced by or transformed into an isotopically depleted “oceanic-type” mantle. Such a process appears to have occurred in the eastern North China Craton as well as the eastern Yangtze block, probably in response to subduction of the paleo-Pacific plate beneath East Asia.     

特提斯喜马拉雅带中段东部三叠纪火山岩的地球化学和岩石成因

三叠纪火山岩分布于特提斯喜马拉雅带中段东部,古地理上位于大印度北东部.分别采用原子吸收分光度法、ICP-MS和全岩同位素稀释法对三叠纪火山岩的主量元素、微量元素和Sr-Nd同位素进行了分析,并用来研究其成分特征和成因.岩相学和地球化学指标显示三叠纪火山岩为玄武岩,MgO含量均很低（范围在4.27%～7.72%）,属于演化岩浆.早三叠世热马组和中三叠世桑康组具有较高的TiO2、TFeO和P2O5含量,稀土元素总量和轻重稀土元素的分馏程度均较高,Ti/V、Ti/Y、Zr/Y比值较高,富集高场强元素（如Nb、Zr等）,地球化学特征与峨眉山高Ti玄武岩相似,以更富集La、Ce、Zr、Hf等元素而有别于夏威夷碱性玄武岩,它们属大陆边缘裂谷背景的具有OIB型地球化学特征的碱性玄武岩;晚三叠世涅如组玄武岩以较低TiO2、TFeO和P2O5含量为特征,稀土元素总量和轻重稀土分馏程度均较低,高场强元素（如Nb、Zr等）丰度很低,为大陆边缘裂谷背景的具有E-MORB地球化学特征的拉斑玄武岩.三叠纪玄武岩Nd同位素组成随时间从轻度富集到亏损（εNd（t）=-1.2→-0.5→4.4）,指示岩浆源区具有从轻度富集到亏损的演化趋势.不相容元素（如La/Sm、La/Ta以及（Th/Ta）PM、（La/Nb）PM等）指示热马组和桑康组玄武岩遭受了一定程度下地壳混染,而涅如组没有遭受地壳混染.热马组和桑康组玄武岩还显示岩石圈地幔物质的印记,并与石榴石相二辉橄榄岩的低度部分熔融有关,而涅如组玄武岩除了具有E-MORB特征外,还与尖晶石相二辉橄榄岩的较高程度部分熔融有关.它们被解释为上涌的软流圈地幔物质与岩石圈地幔物质混合后在不同程度的拉张背景下发生减压熔融的产物.特提斯喜马拉雅带的三叠纪裂谷作用很可能具有主动裂谷作用的性质,较小规模的火山岩浆作用可用裂谷带之下上涌的地幔物质由于传导作用而变冷或正在孕育的地幔柱成因模式来解释.     

广西那龙地区中三叠世火山岩地球化学特征及构造意义

右江盆地西南缘广泛出露早—中三叠世火山岩,目前对这些火山岩没有精确的年代学和地球化学研究。本文选择广西那坡县那龙地区下三叠统罗楼组与中三叠统百逢组之间的一套厚层状分布的火山岩作为研究对象,对其进行了LA-ICP-MS锆石U-Pb同位素定年、锆石主微量元素及全岩的地球化学研究。锆石206Pb/238U同位素年龄为241.2±1.9Ma(MSWD=0.69),代表火山岩的结晶年龄。锆石稀土元素总量较高,富集重稀土元素,具有明显Eu负异常及Ce正异常,含有较低的Th、Th/U、Ce/Sm和δEu值及相对较高的Hf、Yb/Gd和U/Ce值,指示原岩岩浆源区有地壳熔体的组分。火山岩全岩SiO2含量为51.28%～56.17%,并显示低TiO2含量(0.79%～1.28%)和高Al2O3含量(13.52%～15.51%)的特征。稀土元素地球化学特征表现为Eu负异常(δEu=0.60～0.71),富集大离子亲石元素(Rb、Cs、Ba、U、Sr、Pb、Th、K)和轻稀土元素而亏损高场强元素(Nb、Ta、Zr、Hf、P、Ti)及重稀土元素,与岛弧火山岩的特征一致。Ce/Pb及Nb/U值接近大陆地壳,Zr/Y值和Zr含量偏高,表明原始岩浆源区可能为地壳熔体和俯冲洋壳熔体组成的混合物,岩浆在形成上升过程中有深海沉积物或地壳物质的加入,岩石成因与俯冲作用有关。但Ba/Th值(2.92～69.75)小于300,表明原始岩浆在上升过程中受到流体混染的程度比较小。结合前人研究成果可得出,广西那龙中三叠世岛弧火山岩的发现,代表早中生代古特提斯洋东延部分存在一个俯冲消减带。     

朝鲜半岛咸北地区晚二叠世基性火山岩的地球化学特征:岩石成因与地质意义

晚古生代火山作用既是探究朝鲜半岛北部大地构造归属的基本要素,又是认识东北亚大陆两大构造域转折之际地球动力学过程的关键窗口。针对咸北地区会宁基性火山岩开展的离子探针锆石U-Pb年代学和地球化学研究表明,其喷发时代为晚二叠世(257±3Ma);主要岩石类型包括玄武安山岩和安山岩,其Si O2含量介于51.9%~55.3%,Mg#变化于40~58,属于钙碱性系列;岩石富集大离子亲石元素、亏损高场强元素(如Nb,Ta,Ti),并具有高正的锆石εH f(t)(+10~+16)值。元素-同位素地球化学示踪指示该基性火山岩的岩浆源区为俯冲沉积物熔体交代而形成的不均一岩石圈地幔,其部分熔融则可能归因于俯冲后的板内伸展背景。会宁基性火山岩不仅为判定咸北地块属于中亚造山带在朝鲜半岛的东延部分提供了岩石学证据,而且与中国相邻地块上的同期岩浆事件一道,构成见证古亚洲洋东段沿西拉木伦-长春-延边一线断裂带最终闭合的空间标记。     

延边地区晚三叠世火山岩的岩石地球化学特征及其构造意义

延边地区晚三叠世火山岩主要由安山岩和流纹岩构成，其中包括少量玄武安山岩。火山岩的岩石化学和地球化学研究表明，晚三叠世火山岩属于亚碱性系列，并具有钙碱性系列演化特征，位于中钾和高钾钙碱性岩系列范围。岩石组合、主要元素和稀土元素(REE)等显示晚三叠世火山岩的形成与活动大陆边缘伸展环境有关，它标志着泛太平洋板块(法拉隆板块)对欧亚大陆作用的开始，同时也标志着古亚洲枸造域的结束。     

青海南山中三叠世中酸性侵入岩的地球化学、 锆石U-Pb年代学特征及构造意义

青海南山位于秦祁昆造山带结合部,大地构造位置特殊,构造演化复杂.对不同期次岩浆岩组合开展岩石地球化学和锆石U-Pb年代学研究,可为区域构造单元划分、构造阶段厘定和深部过程等提供丰富信息.对青海南山地区一些中酸性侵入岩开展岩石地球化学和锆石U-Pb年代学研究,结果如下:切如闪长岩体两个样品206Pb/238U加权平均年龄237.9±2.3 Ma(MSWD=2.1)和241.0±3.2 Ma(MSWD=2.4),黑马河含黑云角闪二长花岗岩体两个样品206Pb/238U加权平均年龄242.7±1.5 Ma(MSWD=0.61)和239.30±2.0 Ma(MSWD=1.7),表明这些侵入体的结晶年龄集中于237~242 Ma,属中三叠世;地球化学上属钠质、富镁、铝不饱和的中钾钙碱性-高钾钙碱性岩石,稀土元素配分模式表现为中等程度右倾、中等程度的负铕异常.年代学和地球化学研究表明青海南山地区中酸性侵入岩形成于后碰撞环境.     

青海南部三叠纪结扎群火山岩地球化学特征及其构造环境分析

对青海南部治多-杂多一带晚三叠世结扎群火山岩进行了主量元素、稀土元素、微量元素及Sr、Nd同位素分析.结果表明:该火山岩是一套主要由玄武质粗面安山岩、粗面安山岩组成的偏碱性岩石,岩石化学上表现为低Ti,高Al;稀土元素特征表现为轻稀土元素富集,轻重稀土呈现较强的分馏并具有轻微的负铕异常;在微量元素地球化学方面,表现为富集大离子亲石元素,高场强元素Nb、Zr、P、Ti相对亏损,略具Ta、Nb槽;在Hf/3-Th-Nb/16及10TiO2-Al2O3-10K2O图解中,样品均落入岛弧火山岩区.火山岩的ISr、εNd(t)变化在0.70728～0.70818、-2.4～-4.2之间,表明形成晚三叠世火山岩的原始岩浆是壳幔混合型.综合上述火山岩的各种地球化学特征,表明该套火山岩形成于岛弧环境,由于晚三叠世班公湖-怒江洋发生海底扩张,甘孜-理塘洋向南西俯冲消减,产生强烈的碰撞造山,地幔物质在上涌过程中,受到陆壳的混染,结扎群火山岩为挤压造山机制下的陆缘火山弧岩石.     

Geochemistry of the Batang Group in the Zhaokalong Area,Yushu, Qinghai: Implications for the Late Triassic Tectonism in the Northern Sanjiang Region,China

The Batang Group in the Zhaokalong area not only hosts an important Fe-Cu polymetallic deposit but also reveal important insights for the Late Triassic tectonism in the northern Sanjiang region. In order to delineate the tectonic setting and evolutionary process of the paleo arc-basin system, geochemical studies on the Batang Group strata have been carried out. The results suggest that andesite in the Zhaokalong area mainly belongs to the tholeiite series and is characterized by obvious fractionation of LREE and HREE, enrichment in LILE and depletion in HFSE, and a distinctly elevated δ~(34)SCDT average of 10.5‰. The sandstone is classified as lithic sandstone, which is also characterized by obvious fractionation of LREE and HREE, as well as weak negative Ce and Eu anomalies. The limestone displays positive Eu anomalies, with δ~(13)CPDB ranging from-1.3‰ to 4.4‰ and δ~(18) OSMOW ranging from 14.6‰ to 22.5‰. These results indicate that the andesite has a dual signature of both arc andesite and rift volcanic rocks, whereas the sandstone may be formed in an active continental margin, and the limestone could be deposited in a weak oxidizing shallow sea. The sandstone in the Zhaokalong area represents sedimentation in a platform slope facies, corresponding to the main stage of the Jinshajing oceanic basin subduction during the middle period of Late Triassic. The continental arc volcanic activity resulted from subsequent strengthened subduction, forming the andesite in the North Qiangtang backarc basin. Afterwards, the limestone was formed after the cessation of magmatic activity. The information gleaned from the Batang Group strata helped constrain the evolution of the paleo-Jomda island arc and Jinshajiang oceanic subduction in the Late Triassic.     

内蒙古西乌旗格尔楚鲁晚三叠世流纹岩年代学、地球化学特征及其地质意义

为确定西乌旗格尔楚鲁地区的一套浅色流纹岩的形成时代及其成岩构造环境,进而为探讨古亚洲洋闭合时间提供新的证据,本文对其开展了锆石U-Pb年代学、岩石学和地球化学研究。结果表明,流纹岩形成于221±1Ma;岩石富硅碱、贫钙镁、高Ga/Al值,A/CNK1;轻、重稀土元素分馏不明显,具有显著的Eu负异常;强烈亏损Sr、P、Ti,富集Zr,具有A2型花岗岩的特征,其成因可能是造山后伸展环境下幔源岩浆的底侵和地壳减薄,暗示研究区在三叠纪已经处于伸展背景,古亚洲洋在三叠纪之前已经闭合。研究区三叠纪伸展背景之下的岩浆活动始于早三叠世并一直持续到晚三叠世。     

Geochemistry and geochronology of mafic rocks from the Spanish Central System:Constraints on the mantle evolution beneath central Spain

The Spanish Central System(SCS) contains several suites of Palaeozoic mafic igneous intrusions with contrasting geochemical affinity:Ordovician tholeiitic metabasites,Variscan calc-alkaline gabbros(Gb1) and microdiorites(Gb2),shoshonitic monzogabbros(Gb3) and alkaline diabases and lamprophyres(Gb4).Not all of these rocks are accurately dated,and several aspects of their genesis are still poorly understood.We present new whole-rock geochemical data(major and trace elements,and Sr-Nd isotopes),U-Pb and Lu-Hf isotopic ratios on magmatic zircons and 40 Ar/~(39)Ar amphibole geochronology results in order to establish a precise chronology for the successive events of magmatism in the SCS,and discuss the nature of their mantle sources.Accurate ages have been determined for the Variscan gabbros(305-294 Ma),the microdiorites(299 Ma) and the accompanying felsic porphyries(292 Ma),the shoshonitic monzogabbros(285 Ma),and the alkaline diabases(274 Ma) and monzosyenites(271-264 Ma).According to this information,the Variscan mafic magmatism would be mainly concentrated in the range of 305-294 Ma,with a final manifestation represented by the minor shoshonitic dykes.The alkaline magmatism proved to be slightly older than previously thought and yielded at least two distinct pulses:diabases and lamprophyres-monzosyenites.Zircon Hf isotopes evidence the involvement of depleted and slightly enriched mantle sources.The bulk of the eHf values are in the broad range of-8 to+11,indicative of melting both depleted and enriched mantle regions.The high within-sample Hf isotope variation(up to-11 epsilon units) shown by samples from the Variscan series(gabbros,microdiorites and monzogabbros) could be explained mainly by hybridisation of magmas derived from heterogeneous lithospheric mantle sources.Pressure estimates indicate that the Variscan mafic magmas were extracted from the lithosphere.The Nd-Hf isotopic composition of these suites of rocks suggests the recycling of pelitic sediments during the Cadomian orogeny.Deeper(asthenospheric) mantle levels were involved in the generation of the alkaline suite,whose anomalous negative eHf values(moderately decoupled with respect to radiogenic Nd) could be associated with subducted oceanic components raised by mantle upwelling associated with lithosphere thinning and extension during the Permian.     

青海祁漫塔格地区岩石地球化学特征对三叠纪 多金属矿床找矿的指示

《找矿突破战略行动纲要（2011~2020年）》指出,加强基础地质调查与研究和以油气、铁、铜、铅、锌等为重点加强能源矿产勘查是找矿突破战略行动的重要任务。青海祁漫塔格地区位于东昆仑成矿带,是我国首批国家级整装勘查区之一,也是我国西部Fe、Cu、Pb-Zn矿产最重要和最有找矿潜力的地区之一。近年来,随着找矿突破战略行动的实施,该地区找矿工作取得了一系列重要的成果,但是在多金属矿床找矿方面一直没有取得较大的突破。区内多金属矿床主要与三叠纪花岗质岩石有关,其成矿作用的复杂性和多样性在国内外都十分罕见（丰成友等,2012;赵一鸣等,2013）。然而,到目前为止,对于该地区成矿规律的研究仍然较薄弱,严重制约了进一步的找矿工作。因此,查明成矿规律,寻找新矿产地、推进找矿突破,刻不容缓。本文在区内多金属矿床与三叠纪花岗质岩石存在密切成因联系的基础上,从岩石地球化学特征出发,提出了初步的找矿建议。     

青海祁漫塔格中晚三叠世花岗岩:年代学、地球化学及成矿意义

地处柴达木盆地西南缘的青海祁漫塔格地区不仅是一个特征显著的构造-岩浆岩带,而且也是重要的多金属成矿带。本文对该区中晚三叠世花岗岩开展了详细的年代学、岩石地球化学及Sr-Nd-Pb同位素组成研究,并探讨了成矿意义。结果表明,本区中晚三叠世花岗岩均系准铝质到弱过铝质高钾钙碱性花岗岩类,晚三叠世花岗岩具有更高的K2O/Na2O比值,富集大离子亲石元素(LILE)和轻稀土元素(LREE),明显亏损高场强元素(HFSE),中等初始锶比值和偏负的εNd(t)值表明它们主要源于古老地壳物质的深熔或重熔,并可能有幔源物质的加入;发育闪长质暗色微粒包体的中三叠世花岗岩锆石U-Pb年龄为230～237Ma,大多具斑状或似斑状结构的晚三叠世高分异富钾花岗岩形成于204～228Ma,表明大约240Ma祁漫塔格主造山已由挤压转入伸展并伴有幔源岩浆活动,晚三叠世后演化到后碰撞阶段;中晚三叠世花岗岩与本区密集产出的矽卡岩型和斑岩型多金属矿床的时空与成因关系密切,具有重要找矿指示意义。