藏北双湖鄂柔地区变质岩和玄武岩的40Ar/39Ar年龄及其意义

在藏北龙木错—双湖缝合带东段双湖鄂柔地区,获得绿泥阳起石片岩中阳起石矿物的40Ar/39Ar坪年龄为(235·9±2·6)Ma和枕状玄武岩中蚀变辉石斑晶的40Ar/39Ar坪年龄为(232·5±2·4)Ma,两个年龄具有极好的一致性,记录了中三叠世晚期—晚三叠世早期沿龙木错—双湖缝合带发生俯冲碰撞作用的构造-热事件。羌塘地区中三叠世晚期—晚三叠世早期的俯冲碰撞造山事件使得龙木错—双湖缝合带及其以北的大部分地区(即北羌塘盆地)转变为前陆盆地,区域上三叠统底部不整合面和底砾岩的发育是碰撞造山作用地质记录的重要标志。绿泥阳起石片岩的原岩主要为富含玄武岩的火山-沉积岩系,绿泥阳起石片岩和蚀变枕状玄武岩具有Ti O2、P2O5、MgO含量较高和LREE富集型、无Eu异常,以及“大隆起”微量元素配分模式和富集Nb、Ta、Ti元素等地球化学特征,显示为较典型的洋岛型碱性玄武岩性质。     

A Paleogeographic and Depositional Model for the Neogene Fluvial Succession,Pishin Belt,Northwest Pakistan: Effect of Post Collisional Tectonics on Sedimentation in a Peripheral Foreland Setting

Detailed facies analysis of the Neogene successions of the Pishin Belt (Katawaz Basin) has enabled documentation of successive depositional systems and paleogeographic settings of the basin formed by the collision of the northwestern continental margin of the Indian Plate and the Afghan Block. During the Early Miocene, subaerial sedimentation started after the final closure of the Katawaz Remnant Ocean. Based on detailed field data, twelve facies were recognized in Neogene successions exposed in the Pishin Belt. These facies were further organized into four facies associations i.e. channels, crevasse splay, natural levee and floodplain facies associations. Facies associations and variations provided ample evidence to recognize a number of fluvial architectural components in the succession e.g., low‐sinuosity sandy braided river, mixed‐load meandering, high‐sinuosity meandering channels, single‐story sandstone and/or conglomerate channels, lateral accretion surfaces (point bars) and alluvial fans. Neogene sedimentation in the Pishin Belt was mainly controlled by active tectonism and thrusting in response to the oblique collision of the Indian Plate with the Afghan Block of the Eurasian Plate along the Chaman‐Nushki Fault. Post Miocene deformation of these formations successively caused them to contribute as an additional source terrain for the younger formations.     

Structural and Chronological Evidence for the India-Eurasia Collision of the Early Paleocene in the Eastern Himalayan Syntaxis, Namjagbarwa

The eastern Himalayan syntaxis in Namjagbarwa is a high-grade metamorphic terrain formed by the India-Eurasia collision and northward indentation of the Indian continent into Asia. Right- and left-lateral slip zones were formed by the indentation on the eastern and western boundaries of the syntaxis respectively. The Dongjug-Mainling fault zone is the main shear zone on the western boundary. This fault zone is a left-lateral slip belt with a large component of thrusting. The kinematics of the fault is consistent with the shortening within the syntaxis, and the slipping history along it represents the indenting process of the syntaxis. The Ar-Ar chronological study shows that the age of the early deformation in the Dongjug-Mainling fault zone ranges from 62 to 59 Ma. This evidences that the India-Eurasia collision occurred in the early Paleocene in the eastern Himalayan syntaxis.     

秦岭印支期构造背景、岩浆活动及成矿作用

秦岭造山带以其独特的大地构造位置、复杂的地质演化和丰富的矿产资源而成为地质科学研究的焦点,科学家已经基本清楚了其大地构造格局和地质演化轮廓,共识其在印支期(三叠纪:251～199.6Ma)彻底实现了由海盆向大陆造山带的转变。但是,盆山转变的过程细节、洋盆闭合的时间、三叠纪大地构造属性以及相关的岩浆作用和成矿作用研究薄弱,认识分歧较多。笔者通过综合分析地质、地球物理、地球化学、矿产资源等方面的研究成果,认为三叠纪的秦岭恰似现今地中海,并存着洋陆俯冲和陆陆碰撞,并逐渐由洋陆俯冲转变为陆陆碰撞体制;秦岭古特提斯洋于230～200Ma期间自东向西拉链式缝合,扬子陆块与华北-秦岭联合大陆之间的碰撞造山作用接踵而至;三叠纪的秦岭构造背景并非单一的陆陆碰撞,更非过去认为的造山后或碰撞后。秦岭印支期岩浆作用强烈,形成了埃达克岩、钙碱性花岗岩、高钾钙碱性花岗岩、碱性岩、疑似奥长环斑花岗岩、碳酸岩等多种岩浆岩;它们自勉略缝合带向北显示分带性,依次是:阳山—胭脂坝过铝质S型或改造型花岗岩带、南秦岭高镁埃达克质的钙碱性花岗岩带、北秦岭高钾钙碱性花岗岩带、华北克拉通南缘碱性岩-碳酸岩带;印支期岩浆作用的复杂性、多样性、空间分带性和成分极性等特点无法用陆陆碰撞或碰撞后构造体制来解释,而应是勉略洋板块向北俯冲的结果。秦岭印支期成矿作用长期被忽视,但最近已发现有重要经济价值的印支期矿床类型有碳酸岩脉型、造山型和斑岩型钼矿床,卡林型-类卡林型、造山型和斑岩-爆破角砾岩型金矿床,造山型银多金属矿床,表明在洋陆俯冲向陆陆碰撞转变体制的成矿作用强烈、成矿类型多样,印支期矿床的找矿潜力较大。     

大陆碰撞成矿论

基于经典的板块构造而建立的成矿理论已日臻完善,完好地解释了增生造山成矿作用及汇聚边缘成矿系统发育机制,但却无法解释碰撞造山成矿作用及大陆碰撞带成矿系统。通过对青藏高原碰撞造山与成矿作用的详细研究,并与中国秦岭和其它碰撞造山带综合对比,本文系统提出了一套全新的大陆碰撞成矿理论,简称"大陆碰撞成矿论",初步阐明了大陆碰撞带成矿系统和大型矿床的成矿动力背景、深部作用过程和形成机制。该理论认为,伴随大陆三段式碰撞过程而发育的主碰撞陆陆汇聚环境、晚碰撞构造转换环境和后碰撞地壳伸展环境,是大陆碰撞带成矿系统和大型矿床的主要成矿构造背景。对应于三段式碰撞而在深部出现的俯冲板片断离、软流圈上涌和岩石圈拆沉过程,是导致大规模成矿作用的异常热能驱动力。伴随三段式碰撞而分别出现的压-张交替或压扭/张扭转换的应力场演变,是驱动成矿系统形成发育的构造应力机制。大陆碰撞产生的不同尺度的高热流、不同起源的富金属流体流、不同级次的走滑-剪切-拆离-推覆构造系统和张性裂隙系统,是形成成矿系统和大型矿床的主导因素。成矿金属在碰撞形成的壳/幔混源高fO2岩浆-热液系统、地壳深熔低fO2岩浆-热液系统、剪切变质-富CO2流体系统以及逆冲推覆构造驱动的区域卤水系统和浅位岩浆房诱发的对流循环流体系统中,伴随成矿金属的积聚与淀积是形成大型矿床的关键机制。"大陆碰撞成矿论"还强调,完整的大陆碰撞过程可以引发三次大规模成矿作用,形成一系列标示性的大型矿床:在主碰撞陆陆汇聚成矿期,大陆碰撞引发地壳加厚与深熔,产生富W-Sn壳源花岗岩,形成花岗岩型Sn-W矿床;大陆俯冲板片断离诱发软流圈上涌,产生富金属的壳/幔混源花岗闪长岩,形成岩浆-热液型或叠合型Pb-Zn-Mo-Fe矿床;大陆碰撞从变质地体排挤出富CO2流体,在剪切带形成造山型Au矿,从造山带排泄出建造流体,在前陆盆地形成MVT型Zn-Pb矿。在晚碰撞构造转换成矿期,大规模走滑断裂系统诱发壳幔过渡带和富集地幔减压熔融,其岩浆在浅部地壳岩浆房出溶成矿流体,分别形成斑岩型Cu(-Mo-Au)矿床和碳酸岩型REE矿床;深切岩石圈的剪切作用与下地壳变质产生含Au富CO2流体,形成造山型Au矿;逆冲推覆构造驱动地壳流体长距离迁移汇聚、走滑拉分导致流体大量排泄和充填,形成Pb-Zn-Cu-Ag矿。在后碰撞地壳伸展成矿期,新生下地壳部分熔融产生富金属、富水、高fO2埃达克质岩浆浅成侵位和流体出溶,产生斑岩型Cu矿;中上地壳部分熔融层(岩浆房)驱动地热流体系统,在地热区发育热泉型Cs-Au矿,在构造拆离带形成热液脉型Pb-Zn-Sb和Sb-Au矿。     

塔里木盆地西南坳陷发现晚新生代伸展构造

通过认真、系统的地震资料解释, 我们在塔里木盆地西南坳陷首次发现晚新生代正断层。 这些正断层发育于西南坳陷的东北部, 走向 NE-SW, 剖面上组合成堑垒构造, 个别剖面上显示负花状构造特征。 正断层主要发育于新生界, 向上断至的最高层位是第四系更新统下部。 倾向相反的正断层向下交汇后断距消失, 断层继续向下延伸的情况不清楚。 根据断距 变化和生长指数计算, 正断层形成于上新世晚期, 持续演化至更新世早期。 正断层的形成演化过程与以往在阿瓦提凹陷、巴楚隆起和塘沽孜巴斯坳陷发现的晚新生代正断层基本一致, 正断层活动时间为 ca. 3～2 Ma。 它们形成于一个区域性弱伸展构造应力场, 代表印度-亚洲碰撞远程效应下, 塔里木盆地脉式挤压冲断过程中的一个构造间歇期。     

昆仑造山带晚泥盆世沉积特征及构造古地理环境

昆仑造山带基本构造-地层格架奠基于古生代,晚泥盆世是加里东造山旋回和华力西造山旋回转换的关键阶段,加里东碰撞造山和其后的伸展裂陷等记录均存在于晚泥盆世沉积地层中。西昆仑晚泥盆世奇自拉夫组为一套紫红色碎屑岩沉积,属典型的碰撞造山型磨拉石建造,为加里东碰撞造山的产物;东昆仑晚泥盆世黑山沟组和哈尔扎组岩性组合特征与牦牛山组极为相似,均为一套陆相、滨浅海相的碎屑岩、碳酸盐岩和中酸性火山岩组合,为典型的裂陷伸展型磨拉石建造,是晚古生代裂陷伸展盆地演化开始的标志。     

豫西蛇尾秦岭群P-T轨迹定量计算及其地质意义

河南省西峡县北部蛇尾地区秦岭群变质泥质岩系的黑云二长榴线岩中的石榴石成分环带是连续变质反应的结果。本文根据该岩石的石榴石环带成分定量计算了变质作用P-T轨迹。P-T轨迹样式表明,本区秦岭群的变质作用可以分为两大期:第一期发生在大陆碰撞带环境中,变质的温度压力演化受均匀地壳增厚及隆起侵蚀过程控制;第二期发生在岛弧环境或活动大陆边缘环境,变质温压条件早阶段与深部上升的热流有关,中阶段受侵位的炽热花岗岩体控制,晚阶段受地体背冲推覆的构造过程制约。     

Oxygen, carbon, and strontium isotope geochemistry of diamond-bearing carbonate rocks from Kumdy-Kol, Kokchetav Massif, Kazakhstan

Diamond-bearing carbonate rocks from Kumdy-Kol, Kokchetav massif, Kazakhstan, were strongly altered by fluids flowing through fractures and infiltrating along grain boundaries during exhumation. Alteration includes retrogradation of high-grade silicate assemblages by hydrous minerals, replacement of diamond by graphite and of dolomite by calcite. Diamond-bearing carbonate rocks are among the most intensely altered isotopically with δ¹⁸O_VSMOW values as low as +9‰, δ¹³C_VPDB=−9‰, and ⁸⁷Sr/⁸⁶Sr as high as 0.8050. Evidence of isotopic equilibration between coexisting dolomite and high-Mg calcite during ultrahigh-pressure metamorphism (UHPM) is preserved only rarely in samples isolated from infiltrating fluids by distance from fractures. Isotopic heterogeneity and isotopic disequilibrium are widespread on a hand-specimen scale. Because of this lack of homogeneity, bulk analyses cannot provide definitive measurements of ¹³C/¹²C fractionation between coexisting diamond and carbonate. Our study adequately documents alteration on a scale commensurate with observed vein structures. But, testing the hypothesis of metamorphic origin of microdiamonds has not fully succeeded because our analytical spatial resolution, limited to 0.5 mm, is not small enough to measure individual dolomite inclusions or individual diamond crystals.     

新生代埃达克岩两种成因类型的含矿性和源区:西南太平洋带与东太平洋带的对比

埃达克岩是一种新型的火成岩(Sr/Y值≥20),形成于环太平洋带的大洋岛弧、大陆边缘造山带和陆缘火山弧环境,依据REE配分模式可将其划分为两种成因类型:大洋型(O-型)埃达克岩和大陆型(C-型)埃达克岩。西南太平洋带是世界上新生代埃达克岩和类埃达克岩广泛分布的地区之一。这些中酸性岩浆岩广泛分布于东南亚地区的菲律宾群岛、苏拉威西和加里曼丹中部、印度尼西亚几内亚岛和巴布亚新几内亚至所罗门群岛一带,零星见于班达岛弧、苏门答腊和西爪哇等地。研究结果表明:不同成因类型的埃达克岩具有不同的含矿性,反映各自来源于不同的岩浆岩源区。无论在西南太平洋带还是东太平洋带(智利),C-型埃达克岩(La/Yb值≥12)是俯冲板块的部分熔融作用叠加岩浆上侵过程中MASH(熔融-混染-储存-均一化)和AFC(混染-分异-结晶)作用的产物,与世界级斑岩铜-金矿床共生;而O-型埃达克岩(La/Yb比值≤12)则与俯冲的海洋平缓板块部分熔融作用有关,在西南太平洋带主要与浅成热泉金矿带和喷气型矿床有成因联系。