吉林通化赤柏松铜镍硫化物矿床Re-Os同位素研究及其地质意义

赤柏松岩浆型铜镍硫化物矿床位于华北克拉通胶辽吉带,含矿镁铁质—超镁铁质岩侵入到鞍山群最下部的四道砬子河组变质岩中;该矿床硫化物矿样品的Os和Re浓度分别为19×10^-3~490×10^-3和0.47×10^-3~13.97×10^-3,对这些数据分析得出了一条6点Re-Os等时线年龄为1 885±94 Ma,矿石的初始(187)^Os/(188)^Os 比值为0.80±0.16 (MSWD=0.17),表明矿石为岩浆源,熔体主要由地幔贡献,但在成矿过程及岩浆侵位期间有不少地壳物质混入成岩成矿系统。新的Re-Os年代学结果表明,赤柏松镁铁质—超镁铁质侵入体与铜镍矿床形成于古元古代,而不是前人认为的早白垩世。     

桂北龙胜上朗变镁铁质岩锆石UPb年龄及其地质意义

本文采用LAICPMS锆石UPb测年对桂北龙胜地区上朗变镁铁质岩进行年代学研究。2件年代学样品给出近乎一致的年龄信息,集中在(114.8±1.6)、(152.0±5.0)、(213.9±3.5)、(274.6±9.4)、(442.5±6.7)、(553.5±9.2)、(774.2±5.9)和(822.0±10.0) Ma等8个年龄峰值。锆石成因类型研究表明,(774.2±5.9) Ma锆石为样品中最年轻的岩浆锆石,代表上朗变镁铁质岩的侵位时代。UPb年龄大于(822.0±10.0) Ma的锆石为捕获锆石,代表岩浆侵位过程中捕获物质的时代。(114.8±1.6)、(152.0±5.0)、(213.9±3.5)、(274.6±9.4)、(442.5±6.7)和(553.5±9.2) Ma为热液锆石年龄,代表变镁铁质岩成岩后遭受后期构造热事件影响的时限。其中,(442.5±6.7) Ma代表寿城—三门断裂韧性变形的时代,与区域NNE向韧性断裂的变形时代一致。而小于(442.5±6.7) Ma的热液锆石年龄,表明岩石韧性变形后遭受多期构造热事件的影响。泛非期(553.5±9.2) Ma热液锆石的存在,表明华南大陆曾受泛非构造热事件的影响,应具有冈瓦纳大陆的亲缘性。     

湖北红安群的时代：变质花岗质侵入体U－Pb定年提供的制约

湖北红安群的原岩形成时代一直是个有争议的问题。笔者对红安群中两个不同类型的花岗质侵入体进行了锆石U-Pb定年,在位于红安群之下的双峰尖岩体中获得岩浆侵位年龄为(813±6)Ma,在侵入于红安群中的高格岩体获得岩浆侵位年龄为(638±142)Ma,高压变质年龄为(229±22)Ma。结合目前在扬子板块和大别造山带内部获得的一系列新元古代年代学数据,认为红安群变质杂岩中沉积地层的形成时代应限制在825～630Ma之间,是扬子大陆基底在新元古代裂解的产物。这套岩石在印支期(约230Ma)华北与扬子板块碰撞过程中经历了低温高压蓝片岩—榴辉岩相变质作用。     

川南平川镁铁质-超镁铁质岩锆石U-Pb年龄及地质意义

为探讨镁铁质-超镁铁质岩的岩石学特征及成岩成矿作用时间序列, 完善区域成岩成矿年代学格架, 对平川地区的镁铁质-超镁铁质岩进行了元素地球化学分析和LA-ICP-MS锆石U-Pb定年.测试结果显示, 黄草坪辉长岩成岩年龄为259.7±1.2 Ma, 其捕获锆石结晶年龄为269.8±2.4 Ma, 辉绿(玢)岩等次火山岩参考成岩年龄为248± Ma, 其变质锆石年龄为67± Ma.研究结果表明, 平川地区的镁铁质-超镁铁质岩产出于大陆裂谷环境, 岩浆源区来自上地幔尖晶石相二辉橄榄岩, 为一套同源异相有利于铁矿化形成的富钠质拉斑玄武质岩石系列.岩浆活动开始孕育时间不晚于269.8±2.4 Ma, 大规模岩浆活动发生于259.7±1.2 Ma, 其约束了岩浆分异型和火山喷发(溢)沉积型矿化的成矿时间, 次火山岩的成岩年龄约束了次火山热液型矿化的成矿时间上限, 变质锆石U-Pb年龄记录了平川地区经历了喜马拉雅期陆内造山作用.平川地区构造岩浆活动具有爆发性、阶段性和成矿专属性等特点, 镁铁质-超镁铁质岩的形成可能与岩石圈的大规模减薄作用有关, 攀西地区海西-印支期的成岩-成矿作用为同源岩浆受区域统一深部地球动力学背景约束演化的异相产物.      

碰撞后岩浆作用与陆壳生长：以柴北缘超高压变质带为例

碰撞后岩浆活动对于了解造山带垮塌和去根过程及陆壳生长具有重要意义.总结了柴北缘超高压变质带中形成于400～360 Ma的碰撞后花岗岩-辉长岩侵入体和镁铁质岩脉的年代学和地球化学特征.其中，花岗岩侵入体具有典型的I-型花岗岩特征，形成于壳幔相互作用的岩浆混合.来自地幔的镁铁质岩脉可以划分为两组：（1）392～375 Ma中基性岩脉；（2）约360Ma超基性岩脉.其地球化学特征表明，镁铁质岩脉的微量元素和同位素随形成时间的变新而逐渐亏损，地幔源区从岩石圈地幔变为软流圈地幔.这种源自地幔的镁铁质岩浆活动是碰撞后岩浆活动开始和造山带垮塌的关键指标.结合碰撞后岩浆作用的特征，提出了一个地球动力学模型来解释柴北缘约35百万年（Ma）的造山带垮塌去根过程，在395～375 Ma发生缓慢的岩石圈地幔侵蚀，360 Ma前岩石圈发生拆沉作用，岩石圈地幔垮塌，同时软流圈地幔上升.地幔岩浆的加入表明碰撞后阶段是大陆生长的重要时期.     

吉林中部漂河川镁铁-超镁铁质杂岩带的特征：对华北东北缘构造带性质和演化的约束

漂河川镍矿的辉长岩锆石SHRIMPU-Pb定年给出了222Ma±8Ma的年龄,表明其形成于晚三叠世。研究结果表明,该岩体不属于蛇绿岩的成员,而是热侵位的镁铁—超镁铁质岩,侵位时代在区域性的变质变形事件之前。结合地球化学资料、相邻地区的大地构造相及热年代学的研究结果,认为区域上的造山作用主幕很可能发生在中生代,而不是原来认为的二叠纪末。漂河川和相关地区的镁铁—超镁铁质岩应该形成于碰撞造山之前,很可能属于大陆边缘裂谷性质。     

新疆香山杂岩体的成岩与成矿时序

新疆东天山香山地区镁铁-超镁铁杂岩体中产有香山中中型铜镍矿和香山西大型铜镍-钛铁矿床.杂岩体可分为辉长岩类、超镁铁质岩类和钛铁辉长岩类.野外证据表明三者具有先后侵位关系.本文通过对香山杂岩体不同岩相年代学资料梳理,补充了定年数据,获得香山杂岩体侵位年龄为283.2±2.1Ma,验证了不同岩石系列的侵位时序.此外,锆石年龄数据还记录了本地区曾经发生过的构造-岩浆热事件.利用角闪石40Ar/39Ar测年结果,并结合锆石U-Pb测年结果推测香山西岩体侵位较深,香山中岩体侵位较浅,进一步推测西岩体剥蚀量较大,而中岩体剥蚀量较小.结合野外穿插关系,厘定了杂岩体侵入-成矿事件的时序.     

东昆仑造山带中灶火地区早中生代镁铁质岩墙群的成因及地质意义

东昆仑造山带中灶火地区镁铁质岩墙群以闪长玢岩为主,含少量闪斜煌斑岩、辉绿玢岩及辉绿岩,LA-ICPMS锆石U-Pb年代学指示该套岩墙群结晶侵位年龄为(249±1)Ma。稀土元素含量整体较高,富集轻稀土元素(∑REE=99.9×10-6~173.9×10-6,(La/Yb)N=3.5~9.3);微量元素表现出富集大离子亲石元素(LILE),亏损高场强元素(HFSE)的特征;源区分析表明,镁铁质岩浆为俯冲洋壳析出的流体交代富集地幔的结果,且在岩石成因中部分熔融起到主导作用,地壳混染和分离结晶作用对岩浆成分分异起到的作用有限。构造环境分析表明,岩石的形成与俯冲作用有关,结合区域构造演化认为镁铁质岩墙群的成因为:早三叠世,在古特提斯洋向北俯冲的环境下,俯冲板片释放的流体交代富集地幔,诱发地幔部分熔融形成镁铁质岩浆,受弧后伸展的动力学背景影响,岩浆最终上升侵位形成镁铁质岩墙群。     

中条山中生代镁铁质侵入岩年代学与地球化学:对华北克拉通南部岩石圈地幔性质的制约

镁铁质岩石作为幔源岩浆产物,其成因研究有助于探讨华北克拉通深部地幔性质及其演化过程.对中条山地区镁铁质侵入岩开展了系统的锆石U-Pb年代学、全岩主、微量元素、全岩Sr-Nd同位素和锆石Hf同位素研究,揭示了晚三叠世(217±2 Ma)和早白垩世(121±2 Ma)两期镁铁质岩浆活动.晚三叠世镁铁质侵入岩SiO2含量低至...     

内蒙古达茂旗北部闪长岩锆石SHRIMP U-Pb、角闪石~(40)Ar/~(39)Ar年代学及其地质意义

内蒙古达茂旗北部的早古生代闪长岩侵入体产于包尔汉图-白乃庙岛弧带的西部,采用SHRIMP锆石U-Pb定年及角闪石40Ar/39Ar测年对其进行了精确的年代学研究。两件闪长岩样品分别获得的SHRIMP锆石U-Pb年龄为453±3Ma和446.8±5.3Ma,角闪石40Ar/39Ar坪年龄为459.2±2.4Ma和442.9±4.2Ma。这为研究该时期弧岩浆作用提供了新的年代学证据,并表明该岩浆侵位后,经历了结晶并快速冷却的过程,可能揭示了本区岛弧带和华北板块碰撞的构造意义。     

http://www.sciencedirect.com/science/article/pii/S1674987112000618

The Moyar Shear Zone(MSZ) of the South Indian granulite terrain hosts a prominent syenite pluton (～560 Ma) and associated NW-SE to NE-SW trending mafic dyke swarm(～65 Ma and 95 Ma). Preliminary magnetic fabric studies in the mafic dykes,using Anisotropy of Magnetic Susceptibly(AMS) studies at low-field,indicate successive emplacement and variable magma flow direction.Magnetic lineation and foliation in these dykes are identical to the mesoscopic fabrics in MSZ mylonites,indicating shear zone guided emplacement.Spatial distribution of magnetic lineation in the dykes suggests a common conduit from which the source magma has been migrated.The magnetic foliation trajectories have a sigmoidal shape to the north of the pluton and curve into the MSZ suggesting dextral sense of shear.Identical fabric conditions for magnetic fabrics in the syenite pluton and measured field fabrics in mylonite indicate syntectonic emplacement along the Proterozoic crustal scale dextral shear zone with repeated reactivation history.     

太行山北段中生代岩基及其包体锆石U-Pb年代学和Hf同位素性质及其地质意义

太行山北段出露大规模中生代岩浆岩带,以中酸性岩为主,普遍含有基性微粒包体。锆石的SHRIMP U-Pb年代学研究表明,包体形成于126Ma左右,与寄主岩石大致同时形成。锆石的LA-MC-ICPMS Lu-Hf同位素原位测量研究表明,基性岩来自富集地幔的部分熔融,并遭受了一定程度的地壳混染;主要的中酸性岩基形成于壳幔岩浆混和过程,而岩基中微粒基性包体是经历分离结晶的基性岩浆注入酸性岩浆房中形成。     

西藏甲玛铜多金属矿床岩浆混合作用及对成矿的贡献

西藏甲玛铜多金属矿床存在明显的岩浆混合作用,对其研究有助于探测地球的深部过程。本文以构造-岩浆事件理论为依据,根据花岗岩类构造组合特征和成因建立了甲玛矿床所在的冈底斯成矿带的构造-岩浆演化序列,阐述了岩浆混合作用发生的直接原因为岩浆底侵作用,论证了混合岩浆的起源机制(源区继承性),可能为约40%的基性端元(镁铁质岩浆)与约60%酸性端元(花岗闪长质岩浆)在15 Ma左右于源区预混合和就位过程中发生的以机械混合为主的再次混合作用;得出了甲玛矿床成矿流体中的金属元素和S主要来源于岩浆混合作用的幔源铁镁质岩浆,暗示岩浆混合对成矿具有贡献。     

川西峨边地区金口河辉绿岩脉SHRIMP锆石U-Pb年龄及其对Rodinia裂解的启示

川西金口河地区中元古代峨边群中发育大量基性侵入岩,其具体侵位时间对厘定峨边群的时限、研究扬子西缘前寒武纪构造属性具有重要意义。对峨边群枷担桥组层型剖面中一条辉绿岩脉进行了SHRIMP锆石U-Pb定年。结果表明,该辉绿岩脉的锆石发育清楚且宽缓的内部环带结构,具有较高的Th/U比值,属典型基性岩浆成因的锆石,其206Pb/238U年龄加权平均值为(813.4±8.2)Ma(MSWD=0.56),代表了该辉绿岩脉的侵位时间,也限定了峨边群枷担桥组的上限年龄。综合扬子西缘新元古代中期基性岩浆活动的最新同位素年龄,证实存在2个主要的活动期:830~800Ma和780~745Ma,且830~800Ma期间基性岩浆活动的峰值年龄为(821±2)Ma。这与前人总结的华南和澳大利亚同期基性岩浆活动的年龄分布特征完全一致,暗示川西金口河辉绿岩脉的形成可能与新元古代导致Rodinia超大陆裂解的地幔柱幕式活动有关。     

内蒙古固阳地区侵入渣尔泰群中新元古代早期辉长岩岩床的发现及其意义

华北克拉通由于新元古代早期构造-岩浆活动的地质记录较少,制约了对其新元古代时期构造演化的认识。本文对内蒙古中部固阳地区侵位于渣尔泰群阿古鲁沟组中3个变辉长岩岩床样品进行了锆石LA-ICP-MS U-Pb年代学测试,显示其侵位年龄为-925 Ma,表明华北克拉通北缘存在新元古代早期的岩浆活动。该岩床与同时期华北克拉通中部-925 Ma的基性岩墙群(大石沟岩墙)和东南部945-890 Ma的基性岩床群(徐淮-辽东-沙里院岩床)具有相似的岩石地球化学特征和重叠的Nd同位素组成,表明其可能是新元古代早期华北克拉通中—东部发育的大规模基性岩浆活动事件在克拉通北缘的响应,但其规模相对华北克拉通东南缘明显较小。华北克拉通北缘新元古代早期基性岩浆活动的发现,为深入了解华北克拉通北缘新元古代构造演化及其与罗迪尼亚超大陆的关系提供了重要线索。     

Timing of granitic magma mixing in the southeastern Gyeongsang Basin,Korea: SHRIMP-RG zircon data

Late Cretaceous calc-alkaline granites in the Gyeongsang Basin evolved through the mixing of mafic and felsic magmas. The host granites contain numerous mafic magmatic/microgranular enclaves of various shapes and sizes. New SHRIMP-RG zircon U–Pb ages of both granite and mafic magmatic/microgranular enclaves are 75.0?±?0.5 Ma and 74.9?±?0.6 Ma, respectively, suggesting that they crystallized contemporaneously after magma mixing. The time of injection of mafic melt into the felsic magma chamber can be recognized as approximately 75 Ma by field relations, petrographic features, geochemical evolution, and SHRIMP-RG zircon dating. This Late Cretaceous magma mixing event in the Korean Peninsula was probably related to the onset of subduction of the Izanagi (Kula)–Pacific ridge.     

Isotopic responses to basaltic injections into silicic magma chambers: a whole-rock and microsampling study of macrorhythmic units in the Pleasant Bay layered gabbro-diorite complex, Maine, USA

The Pleasant Bay layered gabbro-diorite complex (420 Ma) formed via repeated injections of mafic magma into a felsic magma chamber. It is dominated by repeating sequences (macrorhythmic units) with chilled gabbroic bases which may grade upward into medium-grained gabbro, diorite and granite. Each unit represents an injection of mafic magma into the chamber followed by differentiation. Increases in Sr_i and decreases in )_Ndi with stratigraphic height indicate open-system isotopic behaviour and exchange between the mafic and felsic magmas. Isotopic variations of whole-rock samples in individual macrorhythmic units do not conform to bulk mixing or AFC models between potential parental magmas. Sr isotopic studies of single feldspar crystals from one macrorhythmic unit indicate that exchange of crystals between the resident felsic magma and mafic influxes was important, that some of the rocks contain feldspar xenocrysts, and that the rocks are isotopically heterogeneous on an intercrystal scale. Xenocryst abundance increases with stratigraphic height, suggesting that crystal exchange occurred in situ. The lack of disequilibrium textures in the xenocrystic feldspar indicates the evolved macrorhythmic magma and resident silicic magma were of a similar composition and likely in thermal equilibrium at the time of crystal transfer. Mafic chilled margins are enriched in alkalis and isotopically evolved compared with mafic dikes (representing the parental melts) and suggest rapid in-situ diffusional exchange following emplacement of individual mafic replenishments.     

抚顺南部早前寒武纪变质杂岩的地质事件序列

抚顺南部早前寒武纪变质杂岩是华北克拉通北缘辽北-吉南早前寒武纪变质地块的一个重要组成部分,主要由浑南群石棚子组角闪岩相变质火山岩、火山碎屑岩及相伴生的沉积岩等表壳岩系和侵位于其中的石英闪长质片麻岩、英云闪长质-奥长花岗质-花岗闪长质(TTG)片麻岩和花岗闪长岩-二长花岗岩-钾长花岗岩岩石组合组成。LA-ICP-MS锆石U-Pb同位素分析结果显示,侵位于表壳岩中的石英闪长质片麻岩样品12LN39-3的岩浆结晶年龄为2571±7Ma,指示存在老于该年龄的表壳岩系。英云闪长质片麻岩样品12LN04-1和奥长花岗质片麻岩样品13LB49-3的岩浆结晶年龄分别为2544±4Ma和2550±10Ma,记录了一期重要的英云闪长质-奥长花岗质片麻岩侵位事件。斜长角闪岩(样品12LN25-2)的岩浆结晶的最小年龄为2530±5Ma,指示另一火山喷发阶段。晚期钾长花岗岩样品12LN01-1和奥长花岗质片麻岩样品12LN27-1分别侵位于2522±4Ma和2518±23Ma,说明它们的岩浆作用发生于同一时期。而采自于晚期未变形侵入体的石英闪长岩样品12LN30-2的岩浆结晶年龄为2496±18Ma,与上述表壳岩和深成侵入体的主要变质作用(2510~2470Ma)同期发生。这些年代学结果表明,抚顺南部地区新太古代大规模的铁镁质火山喷发作用在大于2571±7Ma已经发生,紧接着2571±7Ma发生石英闪长质岩浆侵位,在2550±10Ma~2544±4Ma之间发生英云闪长质-奥长花岗质岩浆侵位。接下来铁镁质火山再度喷发(~2530±5Ma),随后为钾长花岗岩和奥长花岗质岩浆的侵位(2522±4Ma~2518±23Ma)。晚期为角闪岩相变质作用时期(2510~2470Ma),伴随一定规模的石英闪长岩侵位。     

Geochronologic Constraints on the Magmatic Underplating of the Gangdise^ Belt in the India-Eurasia Collision： Evidence of SHRIMP II Zircon U-Pb Dating

Abstract  Abundant small mafic intrusions occur associated with granitoids along the Gangdisê magmatic belt. In addition to many discrete gabbro bodies within the granitoid plutons, a gabbro‐pyroxenite zone occurs along the southern margin of the Gangdisê belt to the north of the Yarlung Zangbo suture. The mafic intrusion zone spatially corresponds to a strong aeromagnetic anomaly, which extends ～1400 km. The mafic intrusions consist of intermittently distributed small bodies and dikes of gabbro and dolerite with accumulates of pyroxenite, olivine pyroxenite, pegmatitic pyroxenite and amphibolite. Much evidence indicates that the Gangdisê gabbro‐pyroxenite assemblage is most likely a result of underplating of mantle‐derived magma. Detailed field investigation and systematic sampling of the mafic rocks was conducted at six locations along the Lhasa‐Xigazê segment of the mafic intrusive zone, and was followed by zircon SHRIMP II U‐Pb dating. In addition to the ages of two samples previously published (47.0±1 Ma and 48.9±1.1 Ma), the isotopic ages of the remaining four gabbro samples are 51.6±1.3 Ma, 52.5±3.0 Ma, 50.2±4.2 Ma and 49.9±1.1 Ma. The range of these ages (47–52.5 Ma) provide geochronologic constraints on the Eocene timing of magma underplating beneath the Gangdisê belt at ca. 50 Ma. This underplating event post‐dated the initiation of the India‐Eurasia continental collision by 15 million years and was contemporaneous with a process of magma mixing. The SHRIMP II U‐Pb isotopic analysis also found several old ages from a few zircon grains, mostly in a range of 479–526 Ma (weighted average age 503±10 Ma), thus yielding information about the pre‐existing lower crust when underplating of mafic magma took place. It is believed that magma underplating was one of the major mechanisms for crustal growth during the Indian‐Eurasia collision, possibly corresponding in time to the formation of the 14–16 km‐thick “crust‐mantle transitional zone” characterized by Vp = 6.85–6.9 km/s.     

Timing of Magma Mixing in the Gangdisě Magmatic Belt during the India-Asia Collision： Zircon SHRIMP U-Pb Dating

Abstract  Abundant mafic microgranular enclaves (MMEs) extensively distribute in granitoids in the Gangdisê giant magmatic belt, within which the Qüxü batholith is the most typical MME‐bearing pluton. Systematic sampling for granodioritic host rock, mafic microgranular enclaves and gabbro nearby at two locations in the Qüxü batholith, and subsequent zircon SHRIMP II U‐Pb dating have been conducted. Two sets of isotopic ages for granodioritic host rock, mafic microgranular enclaves and gabbro are 50.4±1.3 Ma, 51.2±1.1 Ma, 47.0±1 Ma and 49.3±1.7 Ma, 48.9±1.1 Ma, 49.9±1.7 Ma, respectively. It thus rules out the possibilities of mafic microgranular enclaves being refractory residues after partial melting of magma source region, or being xenoliths of country rocks or later intrusions. Therefore, it is believed that the three types of rocks mentioned above likely formed in the same magmatic event, i.e., they formed by magma mixing in the Eocene (c. 50 Ma). Compositionally, granitoid host rocks incline towards acidic end member involved in magma mixing, gabbros are akin to basic end member and mafic microgranular enclaves are the incompletely mixed basic magma clots trapped in acidic magma. The isotopic dating also suggested that huge‐scale magma mixing in the Gangdisê belt took place 15–20 million years after the initiation of the India‐Asia continental collision, genetically related to the underplating of subduction‐collision‐induced basic magma at the base of the continental crust. Underplating and magma mixing were likely the main process of mass‐energy exchange between the mantle and the crust during the continental collision, and greatly contributed to the accretion of the continental crust, the evolution of the lithosphere and related mineralization beneath the portion of the Tibetan Plateau to the north of the collision zone.