青藏高原拉萨地块碰撞-后碰撞岩浆作用的三种类型及其对大陆俯冲和成矿作用的启示：Sr-Nd同位素证据

青藏高原拉萨地块是揭示印度与亚洲大陆碰撞的最重要的地区之一,其中广泛发育的碰撞-后碰撞岩浆作用记录了这一地区从特提斯洋俯冲消减到印度大陆陆内俯冲的全过程.本文基于对最新的Sr-Nd同位素资料的分析,从高原岩石圈的三种主要地球化学端元入手,分析了拉萨地块碰撞-后碰撞岩浆作用的类型及其在大陆俯冲与成矿作用方面的意义.青藏高原岩石圈可以分为三种主要的地球化学端元,一是青藏高原北部地球化学省（包括羌塘、可可西里和西昆仑）代表的青藏原始岩石圈地幔地球化学端元,42Ma以来在高原北部广泛分布的钾质岩浆岩的Nd-Sr同位素成分比较均一和稳定,同位素比值的范围较窄,^87Sr/^86Sr=0.707101～0.710536,εNd=-2～-9,tDM=0.7～1.3Ga;二是雅鲁藏布江蛇绿岩代表的新特提斯洋地幔端元,^87Sr/^86Sr=0.703000～0.706205,εNd=＋7.8～＋10,呈印度洋型MORB特征,属于印度洋型地幔域;三是喜马拉雅带地壳基底和花岗岩类显示的喜马拉雅地壳地球化学端元,εNd=-12～-25,^87Sr/^86Sr=0.733110～0.760000,具相对古老的Nd模式年龄,tDM=1.9～2.9Ga.拉萨地块碰撞-后碰撞岩浆作用可以划分出三种地球化学类型,即拉萨地块原地型、亲特提斯洋型和亲喜马拉雅型.这三种岩浆作用类型受控于上述三种地球化学端元在其源区的比例及相互作用.其中,拉萨地块原地型与青藏高原北部地球化学省特征一致,亲特提斯洋型代表了与新特提斯洋俯冲消减及其后的再循环有关的岩浆作用,亲喜马拉雅型岩浆岩的Sr-Nd同位素特征则可能指示了喜马拉雅大陆地壳端元的参与.超钾质火山岩是揭示印度大陆岩石圈向北俯冲的重要证据,印度大陆岩石圈俯冲作用可能同时控制了超钾质岩石和盐类矿床的产出,古老地壳物质作为源区参与了超钾质岩石和盐类矿床的成岩与成矿作用.拉萨地块中部地区的含矿斑岩属于亲特提斯洋型岩浆作用,因此具亲特提斯洋型特征的火山岩、浅成斑岩和深成侵入岩,是进一步寻找铜、钼、金矿床的重要目标.     

青藏高原拉萨地块西部中新世赛利普超钾质岩石的地球化学与岩石成因

西藏拉萨地块西部赛利普中新世碰撞后超钾质火山岩由中国地质调查局地质填图首次发现,露头呈残丘状集中分布于中新世赛利普盆地,为一套含地幔包体的粗面岩,SiO_2含量中等(55.36%～6.70%),高K_2O含量(6.70%～7.50%)和K_2O/Na_2O比值(3.34～4.93)。岩石高MgO(6.4%～7.95%)、Cr(174×10~(-6)～421×10~(-6))、Ni(268×10~(-6)～337×10~(-6))和Mg~#(68～72),岩石为地幔部分熔融的原始岩浆。岩石高度富集大离子亲石元素(LILE)和轻稀土元素(LREE)、具有明显的Nb、Ta、Ti的负异常、富集放射性成因Sr、Pb及Nd同位素(~(87)Sr/~(86)Sr=0.727327～0.727803,~(206)Pb/~(204)Pb=18.705～18.779,~(207)Pb/~(204)Pb=15.731～15.761,~(208)Pb/~(204)Pb=39.775～39.919,~(143)Nd/~(144)Nd=0.511848～0.511861)、较低的ε_(Nd)值(≈15)和古老的Nd模式年龄(t_(DM)=2.2～2.4 Ga),这些地球化学特征揭示出赛利普的岩浆源区为富集地幔(EMⅡ)。将赛利普与拉萨地块西部其他地点和青藏高原北部的北羌塘和西昆仑地区出露的超钾质岩石进行综合对比表明,赛利普超钾质岩石可能为尖晶石相含金云母橄榄岩及少量石榴石相含金云母橄榄岩地幔的低度部分熔融的产物。拉萨地块超钾质岩石的形成可能与印度大陆岩石圈俯冲,或是俯冲的印度大陆地壳前缘撕裂和分段俯冲有关。     

青藏高原Pb同位素地球化学及其意义

根据青藏高原不同构造单元基底片麻岩、花岗岩类和火山岩等不同类型岩石的486套Pb同位素数据的整理和分析,发现青藏高原岩石圈存在3种主要类型,即亏损Pb同位素的特提斯洋地幔域端元、富集Pb同位素的喜马拉雅成熟大陆地壳端元和青藏高原北部的过渡型Pb同位素的地幔端元。这3类地球化学端元与前人通过Sr-Nd同位素研究获得的3类端元一致。拉萨地块内部不同类型岩石的Pb同位素地球化学特征指示出两类岩浆作用,一类是特提斯洋岩石圈俯冲消减再循环和亏损地幔物质注入导致的亲特提斯洋型岩浆作用,另一类是与类似于喜马拉雅大陆地壳物质加入导致的富集地幔源区有关的超钾质岩浆作用。岩浆作用的Pb同位素地球化学记录了特提斯洋俯冲消减作用和随后发生的印度大陆向北拼合、碰撞和俯冲过程,也记录了大规模的壳幔相互作用对高原岩石圈演化与隆升的贡献。     

青藏高原南部与北部新生代高镁钾质岩地球化学对比:南北地幔源区差异

青藏高原广泛分布有一些新生代高镁钾质岩(MgO≥6%,K_2O/Na_2O>1),通常认为它们应起源于地幔源区,虽然它们均有着富钾、富集大离子亲石元素和亏损高场强元素的共同特征,但青藏高原南部和北部的这些新生代火山岩在形成时代和地球化学特征方面均有明显的不同。青藏高原南部和北部新生代火山岩在形成时间和空间上是不连续的。青藏高原南部和北部的高镁钾质岩可能均源于与古俯冲环境相联系的富集地幔源区,但它们的地幔源区矿物组成和形成深度却是不同的;高原南北高镁钾质岩明显不同的组成可能是因它们源区的壳源物质的来源或含量不同所致,而高原南部比北部高镁钾质岩明显低的~(143)Nd/~(144)Nd但高的~(87)Sr/~(86)Sr同位素比值特征,暗示后者起源于一个相对亏损的(含较少沉积物组分的)富集地幔源区。虽然对流减薄和陆内俯冲模式分别可以解释青藏高原抬升和与其共生的新生代火山岩的部分现象,但从总体上看北向俯冲的印度岩石圈的多次断离和南向俯冲的亚欧板块相结合的模式可能是解释新生代以来青藏高原的抬升和与其共生的火山岩最有效的形成机制。     

藏西措勤含铜岩系的物质来源与成因

青藏高原中西部措勤县城东南(约100km)的日阿铜矿区发育两种矿化类型,一种是与二长花岗斑岩岩株有关的夕卡岩型铜矿化,另一种是与辉绿玢岩岩脉有关的细脉浸染型铜矿化。Nd、Sr同位素分析表明,它们以高87Sr/86Sr比值,低143Nd/144Nd比值和负εNd(t)为特征,清楚地显示出地壳组分的特点;Pb同位素则以富含放射性成因Pb为特征,206Pb/204Pb,207Pb/204Pb,208Pb/204Pb比值分别为18.672~18.926,15.630~15.685和39.018~39.432,显示出俯冲板片组分在岩浆形成过程中的作用。Nd、Sr、Pb同位素分析表明,它们形成于碰撞后伸展环境。在该环境下,富集的大陆岩石圈地幔发生部分熔融形成的具OIB特征的镁铁质岩浆底侵与地壳岩石相互作用形成了措勤含铜岩系。这个岩系产生于拉萨地块内,从俯冲带演化历史来看,它与南部的印度河-雅鲁藏布江洋壳的俯冲无关,而是北部班公湖-怒江洋壳向南俯冲的结果。     

长白山地区新生代火山岩的岩石化学及Sr、Nd、Pb同位素地球化学研究

通过主元素、稀土元素、Sr、Nd、Pb同位素地球化学特征并结合板块俯冲模式来讨论长白山地区新生代火山岩系的形成和演化。大部分样品都进入上地幔Sr演化范围,具低Sr高~(87)Sr/~(86)Sr特点;∑Nd介于-2.3—+2.9之间;不同岩性熔岩的Pb同位素组成变化不大。主元素、REE模式和同位素的资料都证实区内火山岩是源自上地幔的同源岩浆分异演化而成,并有地壳物质的混染。     

青藏高原中新生代花岗岩Sr、Nd同位素研究

青藏高原中新生代岩浆活动强烈，本文报道青藏高原西部中新生代代表性花岗岩的Sr，Nd同位素测定结果，结合前人已发表的东部地区花岗岩同位素资料，初步探讨了青藏高原地区中新生代花岗岩的Sr，Nd同位素组成、物质来源与成因。研究表明，分布于冈底斯地块北南边界(即冈底斯花岗岩北带和南带)与洋壳俯冲有关的燕山晚期花岗岩，具有低^87Sr／^86Sr初始值(小于0．706)、正εNd(t)值和年轻的t2DM模式年龄的特征，岩浆来源于俯冲洋壳的熔融；与陆-陆碰撞及碰撞后有关的冈底斯花岗岩^87Sr／^86Sr初始值变化大(0．706～0719)，而εNd(t)值和t2DM都在很小范围变化，Sr、Nd同位素组成似乎与时代、岩性无关，说明壳幔混合花岗岩的同位素源区长时期保持相对均一。无洋壳物质参与的通过陆内俯冲作用形成的喜马拉雅区花岗岩，具有高^87Sr/^86Sr初始值(大于0.720)、古老模式t2DM年龄(1792～2206Ma)和低εNd(t)值(-10．3～-16．3)特征，并与基底岩石的Sr，Nd组成一致，岩浆源区为壳源。由此说明花岗岩类及其岩石组合的形成主要取决于深部部分熔融物质的成分，不同火成岩组合的差异反映了青藏高原岩石圈组成和演化的不均一性。     

长江中下游地区蝌蚪山晚中生代玄武岩的地球化学研究: 岩石圈地幔性质与演化的制约

长江中下游地区繁昌火山盆地蝌蚪山晚白垩世玄武岩为硅饱和岩石, SiO2含量在 47.63%～ 50.02%之间,在 TAS图上位于碱性和亚碱性的分界线上,多数属于玄武岩,少数为粗面玄武岩. MgO含量较低( 3.72%～ 5.58%),但 Mg#值较高( 61～ 71).岩石富集大离子亲石元素 Ba、 Th、 U、 LREE和 Pb,亏损高场强元素 Nb、 Zr和 Ti,具富集的 Sr、 Nd和 Pb同位素组成.初始 87Sr/86Sr(t)比值介于 0.706 5～ 0.706 6之间,ε Nd(t)值介于-5.5～-7.3之间.在 87Sr/86Sr(t)-ε Nd(t)相关图上投在富集的第Ⅳ象限,并趋向于 EMⅡ地幔端员. 206Pb/204Pb(t)、 207Pb/204Pb(t)和 208Pb/204Pb(t)比值分别为 17.928～ 18.311、 15.426～ 15.621和 37.785～ 38.525,在 Pb同位素相关图上处在 DMM和 EMⅡ地幔端员之间.蝌蚪山玄武岩的地球化学特征表明其原始岩浆来源于岩石圈地幔,底侵到壳幔边界后曾有一段时间的滞留,并经历了一定程度的以橄榄石和斜方辉石为主的结晶分异,随后在上升过程中没有受到明显的地壳物质的混染.本地区晚中生代时期陆下岩石圈地幔具有同位素富集的性质,曾受到过古老俯冲事件中析出流体 /熔体的交代.与本地区新生代玄武岩地球化学性质的对比表明,从晚中生代至新生代,由于岩石圈拉张和软流圈的上涌,长江中下游地区发生了岩石圈的减薄,其过程和华北地块东部的岩石圈减薄事件基本一致.造成华北地块东部和华南地块东部的岩石圈减薄具有一致的动力学机制和背景,很可能是晚中生代时期古太平洋板块向亚洲大陆之下俯冲造成的弧后盆地的拉张减薄.     

藏北祖尔肯乌拉山地区新生代高钾钙碱岩系火山岩同位素地球化学研究

通过对藏北祖尔肯乌拉山地区新生代高钾钙碱岩系火山岩Sr,Nd,Pb同位素成分的系统测试分析表明,火山岩具有相对高的^87Sr／^86Sr和低的^143Nd／^144Nd值及高的Pb同位素组成特点,且Sr,Nd,Pb同位素比值变化范围很窄,反映了其具有同源岩浆的特点,并且经历了类似的地球化学动力学过程。Sr,Nd,Pb同位素组成及相关图解判别表明,藏北祖尔肯乌拉山地区新生代高钾钙碱岩系火山岩来源于被大洋沉积物和地壳物质所混合的不均一富集地幔源区,显示源区具有壳幔混源性质,与EMⅡ型富集地幔源特征一致。     

印度-亚洲大陆碰撞过程中新特提斯洋岩石圈的命运

印度-亚洲大陆碰撞之后的新特提斯洋板片的断离过程及其产生的岩浆作用一直是青藏高原南部地质研究中受到广泛关注但存在极大争议的问题.分析了青藏高原南部拉萨地块上新特提斯洋板片断离存在的问题,总结了目前用于限制板片断离过程的岩石学方法.对拉萨地块南部典型地区早新生代镁铁质岩石开展了详细的地质年代学、主微量元素和Sr-Nd-Hf同位素地球化学分析,厘定了~57 Ma和~50 Ma与新特提斯洋板片断离过程密切相关的两套岩石.~57 Ma的镁铁质岩石显示出高的Zr/Y和Ti/Y比值,不同于拉萨地块南部广泛分布的岛弧岩浆地球化学特征,表明它们形成于板内伸展背景下,很可能代表了新特提斯板片断离的开始.~50 Ma的镁铁质岩石为富闪深成岩,反映了印度-亚洲大陆碰撞后南拉萨地块岩石圈中的富水环境,暗示大洋板片断离后仍然持续释放流体至上覆岩石圈地幔中.结合拉萨地块上已有的镁铁质岩石的年代学和地球化学数据,重建了新特提斯洋在印度-亚洲大陆碰撞之后从初始撕裂至板片完全断离的全过程,即新特提斯板片在~57 Ma开始发生初始撕裂,随后以高角度俯冲并与印度大陆岩石圈脱离,导致中拉萨和南拉萨地块同时出现广泛的镁铁质岩浆作用,在~50 Ma大洋板片完全断离.拉萨地块内部岩石圈地幔地球化学组成存在极大的不均一性,中拉萨地块和南拉萨地块东部的局部地区存在古老的岩石圈物质组成,而南拉萨地块中部主要为亏损的岩石圈.拉萨地块内局部古老富集岩石圈可能受到新特提斯洋板片断离后深部地幔物质上涌的影响转变为新生的亏损岩石圈,这一过程很可能促进了拉萨地块的中酸性岩浆大爆发作用和大陆地壳生长.      

江西相山铀矿田成矿物质来源的Nd、Sr、Rb同位素证据

对相山大型火山岩型铀矿田中邹家山和沙洲铀矿床及其赋矿围岩（碎斑熔岩及次花岗闪长斑岩）进行了Nd、Sr、Pb同位素研究。结果表明：成矿期萤石的εNd(t)值（－6．7～-8．3）和初始^87Sr/^86Sr比值（0．7145－0．7207）与赋矿围岩的εNd(t) 值（－6．2～－9．4）和初始^87Sr/^86Sr比值（0．7121－0．7192）相似。在εNd(t)-tl图上，成矿期萤石数据点的投影域与赋矿围岩的基本吻合，均落在相山元古宙基底演化域范围内。成矿期黄铁矿的铅组成在^206Rb/^204Pb-^207Pb/^204Pb关系图上呈线性分布，而火山岩的铅同位素组成位于此相关线低值一端。利用异常铅线的斜率及成矿年龄计算出富铀体质体的形成年龄为144Ma，这与赋矿围岩的成岩年龄（135－140Ma)接近。因此，相山铀矿田成矿物质主要来自富铀的火山－侵入杂岩,而火山－侵入杂岩则是由类似于地表出露的元古宙基底变质岩部分熔融形成的。由引可见，相山铀矿田的成矿物质主要来源于地壳。     

Complete recycling of a magmatic arc: evidence from chemical and isotopic composition of Quaternary trench sediments in Chile (36°–40°S)

Marine Quaternary trench and slope sediments were sampled along the margin of the Southern Andes, Chile between 36° and 40°S. Major and trace element contents indicate only minor influence of weathering and transport fractionation. The whole rock composition of the sediments is similar to the average rock of the Cretaceous to Holocene magmatic arc of this section of the southern volcanic zone. Sr, Nd, and Pb isotope composition of the sediments also resembles closely the average composition of the magmatic arc. The contribution of compositionally distinct Palaeozoic crust, which makes up most of the volume of the forearc, is ~0–20% crustal Sr, Nd, and Pb according to the isotope record of the trench and slope sediments. Input of sediments from the continent into the subduction system was dominated by detritus from the magmatic arc at least for the last 20 My on the basis of the Oligocene to Holocene exhumation history of the margin.     

High‐Precision Sr‐Nd‐Hf‐Pb Isotopic Composition of Chinese Geological Standard Glass Reference Materials CGSG‐1, CGSG‐2, CGSG‐4 and CGSG‐5 by MC‐ICP‐MS and TIMS

To assess the homogeneity of and provide the first Sr‐Nd‐Hf‐Pb isotopic reference values for the Chinese Geological Standard Glasses CGSG‐1, CGSG‐2, CGSG‐4 and CGSG‐5, we measured these isotopes in several measurement sessions over the course of nearly 3 years. The results were obtained by high‐precision MC‐ICP‐MS and TIMS. Our investigation indicates that these CGSG glass reference materials are homogenous with regard to Sr‐Nd‐Hf‐Pb isotopic distribution and are therefore suitable geochemical materials for Sr‐Nd‐Hf‐Pb isotope measurements. Clear differences in Sr‐Nd‐Hf‐Pb isotopic composition were observed between the glasses and the original powdered rock reference materials (CGSG‐2 and GSR‐7, and especially CGSG‐5 and GSR‐2) because of flux addition during preparation of the glasses. The new Sr‐Nd‐Hf‐Pb isotope data provided here might be useful to the geochemical community for in situ and bulk analysis.     

Geochemical and isotopic characteristics and evolution of the Jurassic volcanic arc between Arica (18°30′S) and Tocopilla (22°S), North Chilean Coastal Cordillera

The present-day North Chilean Coastal Cordillera between 18°30′S and 22°S records an important part of the magmatic evolution of the Central Andes during the Jurassic. Calc-alkaline to subordinate tholeiitic members from four rock groups with biostratigraphically constrained age display incompatible element pattern characteristic of convergent plate-margin volcanism, whereas alkaline basalts of one group occurring in the Precordillera show OIB-type trace element signatures. The correlation of biostratigraphic ages, regional distribution, and composition of the volcanic rocks provides a basis for the discussion on geochemical evolution and isotope ratios.Major and trace element distributions of the volcanic rocks indicate their derivation from mantle-derived melts. LILE and LREE enrichments in calc-alkaline basaltic andesites to dacites and some of the tholeiites hint at the involvement of hydrous fluids during melting and mobile element transport processes. A part of the Early Bajocian to ?Lower Jurassic and Oxfordian andesites and dacites are adakite-like rocks with a substantial participation of slab melt and are characterized by high Sr/Y ratios and low HREE contents. The Middle Jurassic tholeiitic and calc-alkaline basalts and basaltic andesites have been transported and partly stored within a system of deep-seated feeder fissures and crustal strike-slip faults before eruption.The isotopic composition of Sr (⁸⁷Sr/⁸⁶Sr_i=0.7032-0.7056) and Nd (εNd_i=2.2-7.1) of the Jurassic volcanic rocks mostly fall in the range characteristic for mantle melts although some crustal components may have been involved. A few samples show slightly more radiogenic Sr isotopic composition, which is probably due to interaction with ancient sea-water. The Pb isotopic composition of the arc rocks is uncoupled from the isotopic composition of Sr and Nd and is dominated by the crustal component. Since the Cretaceous and Modern arc volcanic rocks show Pb isotopic compositions that can be largely explained by in situ Pb isotope growth of Jurassic arc volcanic rocks, we argue that the various Andean arc systems between 18°30′S and 22°S formed on the same type of basement.Most of the investigated samples have high Ba, Zr, and Th concentrations compared to island arc mafic volcanic rocks. About 20% of the Jurassic arc volcanics comprise of dacitic to rhyolitic rocks. These characteristics combined with the Pb isotopic composition that shows the influence of a Palaeozoic (or partly older) basement point to a continental margin setting for the North Chilean Jurassic arc. The distribution of the magmatic rocks throughout time, their textures, and the character of intercalated sedimentary rocks reflect westward movement of the magma sources and of the arc/back-arc boundary relative to the current coast line during the Early Bajocian on a broad front between 19°30′ and 21°S.     

海南岛中北部三叠纪花岗岩源区的锶、钕同位素制约及其意义

海南岛中北部三叠纪花岗岩的锶、钕同位素初始比值分别为I(Sr)0. 7080 ~0. 71505、εNd(t) -10 ~-5,表明这些花岗岩属壳源型,其源岩主要为海南岛结晶基底中元古界抱板群,但受到了幔源岩浆的混染。这些花岗岩所表现出来的基本一致的锶、钕同位素特征,表明测区具有统一的前寒武纪基底。     

新疆东天山康古尔塔格金矿带研究

通过矿床地质和Ｒｂ－Ｓｒ法，Ｕ－Ｐｂ法，＾４０Ａｒ－＾３９Ａｒ法，Ｓｍ－Ｎｄ法生代学及氢，氧，硫，碳，锶，铅等稳定同位素与流体包裹体研究，查明东天康古尔塔格金矿带中浅成低温热液型金矿，韧性剪切带蚀变岩型金矿及花岗岩有关的石英脉型金矿三者大地构造背景相同，成矿时代一致。成矿物质来源相似，流体包裹体成分类同，属同一成矿系列，三者之间主要是成矿地质环境不尽相同，成矿元素组合有差异，控矿构造不同，反映成矿     

Hydrothermal Fe-Si-Mn oxide deposits from the Central and South Valu Fa Ridge, Lau Basin

A series of samples from the Hine Hina hydrothermal field (HHF) and the Mariner hydrothermal field (MHF) in the Central and Southern Valu Fa Ridge (VFR), Lau Basin were examined to explain the source origin and formation of the hydrothermal Fe-Si-Mn oxide deposits. The mineralogy was studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), Mössbauer spectroscopy, and energy-dispersive spectroscopy (EDS). For the Fe-Mn oxide crusts in the HHF, varying amounts of volcanic fragments and some seawater contributions were recognized, along with higher concentrations of Mn, Al, Co, Ni, Zn, Sr, Mo, elevated ∑REE and negative Ce anomalies. In contrast, the Si-rich oxide samples of the MHF were enriched in Cu, Pb and Ba, indicative of proximity to a hydrothermal jet. Moreover, conductive cooling of hydrothermal fluid evoked the Si-rich deposit formation in the MHF. The Sr, Nd and Pb isotope data provided further constraints regarding the source and formation of the Fe-Si-Mn deposits in the VFR by showing that the samples of the HHF are a mixture of three components, namely, hydrothermal fluid, seawater and volcanic materials, whereas the samples of the MHF were dominated by hydrothermal fluids. The seawater had a minor influence on the Nd isotope data, and the Pb isotope data exhibited a close association with the substrate rock and preformed volcaniclastic layers in this area. The occurrence of relatively high Mn/Fe ratios in the hydrothermal deposits of this area may be a good indicator of the propagating activities of the VFR over geological time.     

钾玄岩系列:藏东玉龙铜矿带含矿斑岩Sr、Nd、Pb同位素组成

西藏东部玉龙铜矿带,包括玉龙、扎拉尕、莽总、多霞松多和马拉松多含矿斑岩,马牧普钾质碱性斑岩和总郭碱性火山岩等Sr、Nd、Pb同位素组成比较一致,其数据点均分布在地幔演化区,接近EMI地幔端元,暗示其物质来源于交代地幔源区。     

Plume magmatism in the northeastern part of the Altai–Sayan region: Stages,source compositions,and geodynamics (exemplified by the Minusinsk Depression)

The results of geochronological (U–Pb, Ar–Ar), geochemical, and isotopic (Sr, Nd) studies of the Ordovician and Devonian mafic volcanic–subvolcanic rock associations of the Minusinsk Depression are presented. The obtained ages of magmatic associations and the basite composition, considering previous studies, witness to the impact of two mantle plumes different in age (Late Cambrian–Ordovician and Devonian) on suprasubduction rock complexes in active continental margin settings.     

Isotopes and Geochronology of the Meixian-type Pb-Zn-(Ag)Deposits,Central Fujian Rift,South China:Implications for Geological Events

Central Fujian Rift is another new and important volcanogenic massive sulfide Pb-Zn polymetallic metallogenetic belt. In order to find out the material genesis and mineralization period of Meixian-type Pb-Zn-Ag deposits, S and Pb isotope analysis and isotope geochronology of ores and wall rocks for five major deposits are discussed. It is concluded that the composition of sulfur isotope from sulfide ore vary slightly in different deposits and the mean value is close to zero with the 834S ranging from -3.5‰ to ＋5.6‰ averaging at ＋2.0‰, which indicates that the sulfur might originate from magma or possibly erupted directly from volcano or was leached from ore-hosted volcanic rock. The lead from ores in most deposits displays radioactive genesis character （206pb/204pb〉18.140, 207Pb/204pb〉15.584, 208pb/204pb〉38.569） and lead isotope values of ores are higher than those of wall rocks, which indicates that the lead was likely leached from the ore-hosted volcanic rocks. Based on isotope data, two significant Pb-Zn metallogenesis are delineated, which are Mid- and Late-Proterozoic sedimentary exhalative metailogenesis （The single zircon U-Pb, Sm-Nd isochronal and Ar-Ar dating ages of ore- hosted wall rocks are calculated to be among 933-1788 Ma.） and Yanshanian magmatic hydrothermal superimposed and alternated metallogenesis （intrusive SHRIMP zircon U-Pb and Rb-Sr isochronal ages between 127-154 Ma）.