微细浸染型金矿床成矿机制新探

通过对微细浸染型金矿床矿物流体包裹体的化学组成、金矿物的化学成分、主要共、伴生矿物组合的研讨,结合该类型矿床的成矿环境及金氢化物、金合金氢化物、金羰基化合物的物理化学性质,认为金氢化物、金合金氢化物、金羰基化合物是微细浸染型金矿床金的主要迁移形式。它们从地球深部富氢、富CO强还原环境,随岩浆、热液、热气迁移至地壳浅部,由于压力、温度、pH值下降、Eh值上升,氢、CO逃逸,氧化、分解形成微粒金矿物,沉淀富集形成金矿床。此后,如再发生地质构造、地壳演化运动,微粒金矿物可重新活化,进行接力式迁移、叠加富集。     

苏北东海水晶矿床的形成机理初探

通过对硅的迁移形式和条件、苏北东海水晶矿床中石英流体包裹体的化学成分、部分飘动气体自然、晶洞与水晶的密切相关性以及水晶的共生伴生矿物等的研究,提出该矿床的形成机制为：在地球深部高温高压强还原富氢环境下,硅呈气态硅氢络合物活化并纯化、迁移至地壳浅部低温低压氧化环境,硅氢化物较快氧化形成石英脉,并在有利部位形成石英外壳（晶洞壳）,晶洞内的硅氢化物在温和稳定环境中缓慢氧化,并自由结晶分异纯化形成水晶矿床。     

钛迁移成矿地球化学模式新探索

通过对钛氢化物和钛合金氢化物的形成条件及理化特征、钛矿物的价态及化学成分、钛矿物的共伴生矿物组合、有关矿物中钛的固态包裹体及流体包裹体气相成分的研讨,考虑到氢在地球形成演化中的作用与重大贡献,认为:钛氢化物、钛合金氢化物是钛的重要迁移形式,它们随岩浆、热液从地球深部迁移至地球浅部,在较还原环境形成自然钛、低价钛矿物,在较氧化环境形成钛的高价矿物,并可在有利部位富集形成钛矿床。     

铀的迁移富集机理新探索

描述了铀迁移、富集成矿的新机制。通过对铀氢化物、铀合金氢化物的形成条件及理化性质，铀矿石的矿物流体包裹体物质成分，主要内生铀矿物化学成分及其微观结构，铀矿物的共、伴生矿物组合的研究，并结合地球的形成和演化史，认为铀主要呈铀氢化物、铀合金氢化物从地壳深部迁移至地壳浅部，由于环境发生变化，氢逃逃、氧化，上述氢化物被氧化分解、富集成矿。     

苏鲁超高压榴辉岩中的钛成矿作用:大陆板块汇聚边界的成矿作用

榴辉岩型钛矿床是重要的钛矿床类型之一。苏鲁超高压榴辉岩中的钛成矿作用以金红石型钛矿床为主,其中金红石以变质矿物中的包裹体、晶间颗粒或脉状形式出现。富钛石榴子石是金红石包裹体出溶的初始矿物。岩石地球化学研究表明,有利于金红石成矿的榴辉岩为高钛榴辉岩,其源岩为富钛基性岩。利用红外显微镜对金红石进行的流体包裹体研究表明,金红石中主要存在三类流体包裹体,即型H2O溶液包裹体、型CO2-H2O包裹体和型CH4包裹体,其中I型原生和假次生流体包裹体和型流体包裹体反映出的压力范围为0.6~1.3GPa,与榴辉岩角闪岩相退变质作用的压力相当,说明与这类金红石形成有关的变质流体源于榴辉岩退变质作用所释放的水。苏鲁地区超高压榴辉岩是华南—华北板块碰撞的结果,巨量陆壳物质俯冲—折返形成了多样式的高压—超高压岩石,与此同时也发生了以金红石为主要矿石矿物的钛成矿作用。综合矿物学、岩石学、地球化学等研究,我们提出大陆板块汇聚边界的钛成矿作用应该经历了原岩的初始富集、陆壳物质俯冲过程中钛的成矿作用、俯冲板块折返过程中钛的成矿作用和流体阶段的金红石成矿作用四个主要成矿阶段。     

金银铂族元素成矿机理的新探索

通过对金、银、铂族元素的氢化物，羧基化合物理化性质，贵金属矿物主要和次要化学成分，贵金属矿物的共伴生矿物组合，有关矿物流体包裹体化学成分，类地行星概况，生产实验等相关问题的讨论，认为金、银、铂族元素主要呈单质及其合金氢化物，单质羧基化合物，单质羧基氢化物迁移的。它们随岩浆，热液，热气迁至地壳浅部，由于减压，降温，氧逸度显著加大，Eh、Ph值发生变化，H2，CO逃逸，氧化，形成贵金属的单质及合金矿物，有的还能与硫，硫化氢作用形成贵金属的硫化矿物和硫盐矿物。     

铬的迁移形式、成矿机理新探

通过对地球深部富氢流体、若干金属氢化物及合金氢化物的形成条件与性质、铬矿物的化学成分及其共生伴生矿物的研讨,结合铬铁矿成矿的地质背景,认为铬氢化物、铬合金氢化物是铬成矿的主要迁移形式。它们从地球深部富氢强还原环境随岩浆迁移至地壳浅部,由于H2,CO,CH4等逃逸、氧化,氧逸度大增,温度、压力下降,铬氢化物和铬合金氢化物分解、氧化、固化富集成铬矿床。     

钴的迁移形式成矿机理初探

通过对钴有关化合物的形成条件和理化性质,钴矿床矿物流体包裹体的化学成分、代表性钴矿物的化学成分、共、伴生矿物组合的探究,结合钴成矿地质背景和环境研究认为,钴的氢化物、合金氢化物、羰基化合物、羰基氢化物是内生钴的主要迁移形式。它们形成于地球深部高压、高温、富氢、富CO的强还原环境,通过断裂、裂隙随岩浆、热液迁移至地壳浅部,由于压力、温度骤降,氧逸度渐增、H2和CO逃逸、氧化,上述钴的化合物分解、氧化、硫化、砷化,沉淀富集形成内生钴矿床,并在以后地质事件中进一步叠加富集,形成更富更大的钴矿床。     

钨的迁移形式成矿机理新探

通过对钨羰基络合物及钨合金氢化物的物理化学性质、钨矿床矿物流体包裹体的化学组成、钨矿物的化学成分、主要共生伴生矿物组合的研讨,结合钨成矿的地质背景和环境,认为钨羰基络合物及钨合金氢化物是钨的主要迁移形式。它们形成于地球深部高压、富氢、富CO的强还原环境,随着岩浆、热液、热气迁移至地壳浅部,由于压力、温度下降,氧逸度大增,H2、CO逃逸、氧化,钨羰基络合物、钨合金氢化物分解,氧化形成钨矿物,沉淀富集形成钨矿床。     

锰的迁移形式成矿机理新探

通过对锰氢化物、锰羰基化合物、锰羰基氢化物的形成条件和理化性质,现代火山气体化学成分,现代海底喷口热液流体成分,有关矿床矿物流体包裹体气相成分,有代表性锰矿物化学成分及铁锰结核的物质组构,菱锰矿的碳同位素组成、锰矿物的共生、伴生矿物组合的探究,认为锰氢化物、锰羰基化合物、锰羰基氢化物是原生锰矿的主要迁移形式.它们从地球深部强还原富H2、富CO高压环境通过断裂、裂隙随岩浆、热液迁移至地壳浅部,由于压力、温度骤降,氧逸度大增,H2和CO逃逸、氧化,锰氢化物、锰羰基化合物、锰羰基氢化物分解、氧化、硫化成原生锰矿,经氧化淋(浸)滤,形成锰的高价氧化矿物.     

江苏省新沂市小焦榴辉岩型金红石矿床的特征及成因初探

江苏小焦榴辉岩型金红石矿床是苏鲁超高压变质带中发现的品位最富、连续宽度最大的大型矿床,它与超高压变质榴辉岩密切相关。矿体主要赋存在含金红石的块状榴辉岩中,呈似层状、长条状和透镜状产出。地球化学特征表明榴辉岩的原岩为来自上地幔或壳幔过渡区的基性至超基性岩。金红石在矿石中主要呈包裹体、粒间充填、蚀变残余、热液充填4种赋存形式,分别代表了4个不同的形成及演化阶段。电子探针分析结果显示,在高压、超高压变质作用期间,富含Na的深部流体对金红石的成矿可能起了重要的作用。研究表明该矿床属典型的榴辉岩型金红石矿床,在成因上与超高压变质作用有关,类似于挪威的Engebfjellet、俄罗斯的Shubino矿床和意大利的PianPaludo矿床,而不同于中国已知的主要金红石矿床。此外,通过本次研究以及对普查和勘探资料的总结,提出了该类矿床的主要找矿标志。     

西藏泽当地幔橄榄岩中的异常矿物及其指示意义

雅鲁藏布江蛇绿岩带内多个地幔橄榄岩体产有金刚石、碳硅石等异常矿物组合,为了进一步探讨这些异常矿物形成的物理化学条件,在前人已有的研究基础上,对泽当地幔岩体中526 kg的方辉橄榄岩样品开展人工重砂矿物学研究工作。研究表明,同雅鲁藏布江蛇绿岩带内的其他岩体相似,泽当地幔橄榄岩也选出了包含金刚石、碳硅石、锆石等30余种矿物。异常矿物组合指示泽当地幔橄榄岩中存在局部的超高压、极还原环境,可能经历了复杂的演化过程:即古老地壳物质通过深俯冲或者折沉作用,进入地幔甚至是地幔过渡带(410~660 km),随后经历了超高压、极还原环境的改造,在后续的地幔柱或地幔对流作用中从洋中脊上升至浅部环境并返回到地壳中。该过程中地幔橄榄岩中的异常矿物组合记录了岩石的演化信息,因此开展地幔橄榄岩中异常矿物组合的精细矿物学研究,对认识壳-幔物质交换以及深部地幔动力学过程都有重要的研究意义。     

华中榴辉岩域的岩浆型榴辉岩及其形成机制

中国中部鄂豫皖苏鲁的榴辉岩分布面积约达５００００ｋｍ＾２，构成地球上一个罕见的宏大的榴辉岩域。榴辉岩的主要围岩是长曲质片麻岩，它与榴辉岩不是相同高压变质作用的产物。     

Ultrahigh-pressure eclogite transformed from mafic granulite in the Dabie orogen, east-central China

Although ultrahigh‐pressure (UHP) metamorphic rocks are present in many collisional orogenic belts, almost all exposed UHP metamorphic rocks are subducted upper or felsic lower continental crust with minor mafic boudins. Eclogites formed by subduction of mafic lower continental crust have not been identified yet. Here an eclogite occurrence that formed during subduction of the mafic lower continental crust in the Dabie orogen, east‐central China is reported. At least four generations of metamorphic mineral assemblages can be discerned: (i) hypersthene + plagioclase ± garnet; (ii) omphacite + garnet + rutile + quartz; (iii) symplectite stage of garnet + diopside + hypersthene + ilmenite + plagioclase; (iv) amphibole + plagioclase + magnetite, which correspond to four metamorphic stages: (a) an early granulite facies, (b) eclogite facies, (c) retrograde metamorphism of high‐pressure granulite facies and (d) retrograde metamorphism of amphibolite facies. Mineral inclusion assemblages and cathodoluminescence images show that zircon is characterized by distinctive domains of core and a thin overgrowth rim. The zircon core domains are classified into two types: the first is igneous with clear oscillatory zonation ± apatite and quartz inclusions; and the second is metamorphic containing a granulite facies mineral assemblage of garnet, hypersthene and plagioclase (andesine). The zircon rims contain garnet, omphacite and rutile inclusions, indicating a metamorphic overgrowth at eclogite facies. The almost identical ages of the two types of core domains (magmatic = 791 ± 9 Ma and granulite facies metamorphic zircon = 794 ± 10 Ma), and the Triassic age (212 ± 10 Ma) of eclogitic facies metamorphic overgrowth zircon rim are interpreted as indicating that the protolith of the eclogite is mafic granulite that originated from underplating of mantle‐derived magma onto the base of continental crust during the Neoproterozoic (c. 800 Ma) and then subducted during the Triassic, experiencing UHP eclogite facies metamorphism at mantle depths. The new finding has two‐fold significance: (i) voluminous mafic lower continental crust can increase the average density of subducted continental lithosphere, thus promoting its deep subduction; (ii) because of the current absence of mafic lower continental crust in the Dabie orogen, delamination or recycling of subducted mafic lower continental crust can be inferred as the geochemical cause for the mantle heterogeneity and the unusually evolved crustal composition.     

Near-solidus melts of MORB + 4 wt% H<Subscript>2</Subscript>O at 0.8–2.8 GPa applied to issues of subduction magmatism and continent formation

Experiments on MORB?+?4 wt% H₂O at 0.8–2.8 GPa and 700–950 °C (Liu in High pressure phase equilibria involving the amphibolite–eclogite transformation. PhD dissertation, Stanford University, Stanford, California, 1997; Liu et al. in Earth Planet Sci Lett 143:161–171, 1996) were reexamined for their major and trace element melt compositions and melting relations. Degree of melting diminishes at greater pressures, with corresponding evolution of melt from andesitic at the lowest pressures and hottest temperatures to high-silica rhyolitic at the greatest pressure and coolest temperature. Quartz contributes greatly to the production of near-solidus melts of basaltic eclogite, with the result that melt productivity falls markedly following quartz exhaustion. This limits the extent of melting attainable in the basaltic eclogite portions of sub-arc subducting plates to no more than ~?2?×?the modal wt% quartz in the mafic eclogite protolith. Synthesized residual mineral assemblages lack an epidote-series mineral at temperatures?>?750 °C, and as a result, melts from the rutile eclogite and rutile-amphibole eclogite facies have elevated concentrations of light rare earth elements, U, Th, have elevated Ba, K, and Sr, high Sr/Y, and are strongly depleted in Nb, Y, and the heavy rare earth elements. Models of eclogite partial melt reacting with peridotite of the mantle wedge reproduce major and trace element characteristics of parental arc magmas so long as the proportions of infiltrating melt to peridotite are relatively high, consistent with channelized ascent. Melt mass is estimated to increase roughly three- to ten-fold, consistent with H₂O concentrations of 3–7 wt% in the magmas produced by reaction. Partial melts of subducting basaltic eclogite are predicted to have positive Sr concentration anomalies, relative to Ce and Nd, that persist through melt-peridotite reactions. Primitive arc magmas commonly have positive Sr anomalies, whereas such anomalies are smaller in estimates of the bulk continental crust. Overall, Sr anomalies diminish passing from primitive to more evolved arc volcanic rocks, consistent with extensive mineral-melt differentiation (crystallization, partial remelting) involving plagioclase. On the order of 50 wt% differentiation would be necessary to eliminate Sr positive anomalies, based on geochemical variations in the Cascade and western Aleutian magmatic arcs. Loss to the mantle of cumulates and restites with high Sr anomalies, in abundances broadly equal to the mass of the preserved crust, would be required to form the continents via processes similar to present-day subduction magmatism.     

"罗田穹隆"中的下地壳俯冲成因榴辉岩及其地质意义

在“罗田穹隆”中发现了下地壳俯冲成因榴辉岩．榴辉岩呈透镜状或板状产于含石榴子石条带状片麻岩中．新鲜的榴辉岩主要由石榴子石、绿辉石、金红石等组成．含少量退变质的角闪石、斜长石、紫苏辉石、透辉石、(钛)磁铁矿和石英等．研究区榴辉岩以保留早期麻粒岩相变质矿物残留体以及经受晚期麻粒岩相和角闪岩相退变为特征．指示它们由扬子镁铁质下地壳麻粒岩相岩石俯冲到深部发生变质并形成榴辉岩．然后折返至下地壳发生麻粒岩相退变，由于麻粒岩相退变质阶段仅以后成合晶形式出现．因而它们可能在下地壳停留时间不长．就又进一步被构造抬升至中上地壳而发生角闪岩相退变．大别山造山带乃至扬子板块北缘现今缺乏厚层镁铁质下地壳．它们也很少出露地表．推测这些俯冲的镁铁质下地壳可能已拆离再循环进人地幔．从而为“罗田穹隆”的形成和演化以及大别山高压-超高压岩石的形成与折返机制等研究提供了关键性的岩石学证据。     

中国大陆科学钻探主孔0～4500米变质岩石锆石中保存的超高压矿物包体

中国大陆科学钻探主孔0-4500米的岩心主要由榴辉岩、斜长角闪岩、副片麻岩、正片麻岩以及少量的超基性岩所组成。岩相学研究结果表明,榴辉岩的围岩普遍经历了强烈角闪岩相退变质作用的改造,峰期超高压变质的矿物组合已完全被后期退变质过程中角闪岩相矿物组合所替代。采用激光拉曼技术,配备电子探针和阴极发光测试,发现主孔224件岩心中有121件(包括榴辉岩、斜长角闪岩、副片麻岩和正片麻岩)样品的锆石中普遍隐藏以柯石英为代表的超高压矿物包体,且不同岩石类型锆石中所保存的超高压矿物包体组合存在明显差异。(含多硅白云母)金红石石英榴辉岩锆石中保存的典型超高压包体矿物组合为柯石英 石榴石、柯石英 石榴石 绿辉石 金红石和柯石英 多硅白云母 磷灰石。黑云绿帘斜长角闪岩锆石中保存的超高压矿物组合为柯石英 石榴石 绿辉石、柯石英 石榴石 多硅白云母和柯石英 绿辉石 金红石,与榴辉岩所保存的超高压矿物组合十分相似,表明该类斜长角闪岩是由超高压榴辉岩在构造折返过程中退变质而成。在副片麻岩类岩石,如石榴绿帘黑云二长片麻岩锆石中,代表性的超高压包体矿物组合为柯石英 多硅白云母和柯石英 石榴石等;而在石榴黑云角闪钠长片麻岩锆石中,则保存柯石英 硬玉 石榴石 磷灰石、柯石英 硬玉 多硅白云母 磷灰石和柯石英 石榴石 磷灰石等超高压矿物包体。在正片麻岩锆石中,标志性的超高压矿物包体为柯石英、柯石英 多硅白云母、柯石英 蓝晶石 磷灰石和柯石英 蓝晶石 榍石等。此外,在南苏鲁东海至临沭一带的地表露头以及一系列卫星孔岩心的锆石中,也普遍发现以柯石英为代表的标志性超高压矿物包体,表明在南苏鲁地区由榴辉岩及其围岩的原岩所组成的巨量陆壳物质(方圆>5000km2,厚度超过4.5km)曾整体发生深俯冲,并经历了超高压变质作用。该项研究对于重塑苏鲁-大别超高压变质带俯冲-折返的动力学模式有着重要的科学意义。     

High-P granulites of the Songshugou area (Qinling Orogen,east-central China): Petrography,phase relations,and U/Pb zircon geochronology

High-pressure (HP) granulites provide telling records of mineral reactions at upper mantle to lower crustal levels and key information on the fate of material in subduction systems. The latter especially applies when they abut eclogite and mantle dunite because such rock associations are crucial for understanding the incompletely known processes at the interface of converging plates. A continental arc, active c. 520–395 Ma ago, formed an enigmatic example of such a rock association in the Songshugou area, Qinling Orogen. To unravel the juxtaposition of the distinct rocks, this study combines petrography, phase equilibria modelling, conventional thermobarometry, and zircon U–Th–Pb–Ti–REE analysis. Two mafic HP granulites, which contain the mineral assemblages garnet–clinopyroxene–plagioclase–rutile–mesoperthite–quartz and garnet–clinopyroxene–plagioclase–rutile, experienced peak metamorphic conditions of ≤1.4 GPa, 860°C and ~1.3 GPa, ≥910°C, respectively. During decompression and cooling, at 489 ± 4 Ma, amphibole lamellae unmixed from a clinopyroxene solid solution and orthopyroxene in part replaced garnet. A felsic HP granulite shows equilibration of garnet, perthite, antiperthite, kyanite, quartz, and rutile at 810–860°C, ~1.2 GPa, sillimanite growth during decompression, and upper amphibolite facies cooling at 510 ± 4 Ma. Though the thermobarometric data are just within the methodological errors, the U/Pb zircon ages imply the HP granulites did not evolve coherently. The HP granulites either represent foundered lower arc crust or originated from subduction erosion because their geochemistry is indistinguishable from that of the hanging-wall plate. Published and new pressure–temperature–time–deformation paths converge at ~710°C, ~0.9 GPa, and ≲470 Ma, implying exhumation tectonics juxtaposed the HP granulites with a mélange of eclogite and mantle dunite at lower crustal levels. This study highlights that lower arc crust can comprise material of diverse evolution.     

大别山超高压变质岩的变形历史及折返过程

大别山南部的超高压变质岩在其形成及折返过程中经过5期变形。D₁变形为榴辉岩相前变形,形成于扬子板块北缘陆壳基底的俯冲过程中;D₂变形形成于折返初期(220-210Ma)即超高压变质岩在浮力驱动下折返至下地壳底部的过程中,变形以块状榴辉岩的糜棱岩化及层状榴辉岩和基质的紧密-同斜褶皱为特征;D₃变形发生在折返中期(200-180Ma)即超高压变质岩在南北陆块持续碰撞作用下被挤出并向北逆冲折返至中地壳的过程中,变形以榴辉岩的布丁化和基质的强烈韧性剪切变形为特征;D₄变形是折返晚期(130-110Ma)超高压变质岩在地壳浅部伸展体制下向南滑脱所致;在折返至近地表时,超高压变质岩受到NE向断层(D₅)的切割。     

孟中榴辉岩形成和演化和P-T轨迹

本文研究了江苏东海县孟中榴辉岩富铝单斜辉石中石榴子石出溶作用,利用温压计对榴辉岩中各阶段矿物组合进行了温压估算,由此建立了孟中榴辉岩形成和演化的P-T轨迹。结果表明,该榴辉岩经历了地幔条件下由于降温和可能的升压作用,富铝单斜辉石中出溶石榴子石并形成榴辉岩;榴辉岩构造侵位到高角闪岩相片麻岩基底中;退化变质这3个阶段的演化过程。