北祁连山中段早中奥陶世蛇绿岩中席状岩墙杂岩的发现及其…

作为蛇绿岩套重要组成部分之一的席状岩墙杂岩近来在北祁连山中段南县大岔大坂北坡的早中奥陶世蛇绿岩中被发现，这一发现对于祁连山早古生代蛇绿岩来说尚属首次，而且对于研究绿岩的发展演化及探讨奥陶纪时洋底扩张都有重要意义，席状岩墙杂岩由一系列具单向冷凝边的辉绿岩墙组成，以一墙挨一墙的形式产出，岩墙间无任何填充物，席状岩墙杂岩在矿物组合上，常量元素，稀土元素及良量元素地球化学特征和配分模式，甚至金属硫化物矿化     

冀东新太古代蛇绿岩套基本特征的初步报道

在冀东遵化新太古代构造带内首次识别出了东湾子蛇绿岩套残片，它具备严格意义上蛇绿岩套层序，从顶部到底部依次为变形枕状溶岩和变沉积岩，席状岩墙杂岩，斜长花岗岩，辉长岩杂岩，镁铁质－超镁铁质杂岩堆积岩，超镁铁质构造岩。其中，席状岩墙杂岩规律巨大，由密集分布的基性岩墙组成，并显示特征的单向冷凝边，岩浆构造及层序指示该蛇绿岩套向西掀斜，并因构造变形使层序重复，根据已有的2．67－2．79Ga的Sm-Nd全岩等时线年龄，及其被奥长花岗岩体（锆石U－Pd2501＋18／－16Ma)侵位，可以认为东湾子蛇绿岩套形成于新太古代。它的发现对于早期板块的构造的研究意义重大。     

蛇绿岩中辉长岩的形成和变质过程研究

系统论述了扩张脊之下的洋壳增生模式、辉长岩地球化学特征及其对岩浆源区及岩浆过程的反映,总结了辉长岩在洋底环境和俯冲带中的变质作用及微量元素地球化学行为,并探讨了蛇绿混杂岩带中辉长岩的特点。对典型蛇绿岩的研究表明,在席状岩墙根部区域存在熔体透镜,来自地幔的岩浆在此贮存、分异。蛇绿岩中不同层位辉长岩的成分差异及结构、构造特点反映了该分异过程。辉长岩以及辉长岩中单斜辉石的地球化学特征可以反演岩浆的源区特征和岩浆分异、混合过程。辉长岩发生的洋底变质包括与洋脊附近热液对流相关的绿片岩相-麻粒岩相变质作用和与超镁铁岩蛇纹石化相关的异剥钙榴岩化作用。辉长岩在变质过程中不相容元素的活动性与温度、流体性质以及构造作用密切相关。     

云南新平县双沟蛇绿岩的初步研究

双沟蛇绿岩由基底岩石、辉长—辉绿岩和玄武岩三部分组成。岩相学和地球化学研究表明,双沟斜长二辉橄榄岩中存在地幔交代作用的证据,属于浸染橄榄岩(impregnated peridotite)。蛇绿岩岩石组合中缺少超镁铁质堆晶岩和席状岩墙群,而辉绿岩和玄武岩的化学成分与MORB相拟,表明双沟蛇绿岩的形成机制与大洋中脊环境类似,但岩浆房很小,扩张速度缓慢,推测相当于哀牢山古特提斯小洋盆扩张早期的裂谷阶段的产物。     

藏北羌塘中部桃形湖早古生代蛇绿岩的岩石学特征

桃形湖早古生代蛇绿岩是龙木错－双湖板块缝合带近期的重要发现。通过对桃形湖蛇绿岩进行详细的野外地质调查和岩石学、年代学、地球化学的研究发现,桃形湖早古生代蛇绿岩各单元出露齐全,由下到上分别为变质橄榄岩、超基性堆晶杂岩、堆晶辉长岩、基性岩墙群和枕状玄武岩,在堆晶岩中有不同规模的斜长花岗岩（层）脉体。桃形湖堆晶辉长岩的时代为中奥陶世,并具有大洋中脊型的地球化学特点。桃形湖早古生代蛇绿岩的发现说明龙木错－双湖板块缝合带中存在完整的蛇绿岩组合,同时也是古特提斯洋早期裂解的重要证据。     

蛇绿岩岩石组合及洋脊下岩浆作用

蛇绿岩的岩石组合从下至上分为４个单元,即：变质橄榄岩单元、深成杂岩单元、席状岩墙群杂岩单元和喷出岩单元。各单元的岩石组合是多种多样的：变质橄榄岩单元主要由方辉橄榄岩、二辉橄榄岩和少量纯橄岩及斜长二辉橄榄岩组成;深成杂岩单元单元包括辉长岩－镁铁质堆晶岩和超镁铁质堆晶岩,在深成杂岩和席状岩墙群杂岩单元内在复杂的岩浆侵入事件;喷出岩单元不仅仅由玄武岩组成,还包括安山岩、玻安岩、钠长岩以及乐砾岩、凝灰岩等     

日喀则蛇绿岩研究中的几个问题

日喀则蛇绿岩是中国最著名的蛇绿岩,但是,许多问题存在争论,许多现象没有搞清楚。文中讨论了日喀则蛇绿岩中一些重要的现象以及对目前发现的许多矛盾如何考虑的问题。例如,(1)日喀则蛇绿岩中是否存在席状岩墙群?是否存在席状岩床群?本文认为,席状岩墙群应当是存在的,因为有不对称冷凝边出现。而席状岩床群可能是有问题的,岩床作为侵入体可以出现在许多地方,但是,蛇绿岩中不可能出现席状岩床群,尤其还把它作为蛇绿岩岩石组合的一个单元。笔者认为,所谓的席状岩床群可能是席状岩流群,它不是一个独立的单元,是玄武岩单元下部的成员。(2)日喀则蛇绿岩是否统统是蛇绿岩是一个需要考虑的问题,雅鲁藏布江东西两段出现的岩石组合及其产出背景与日喀则地区的蛇绿岩明显不同,其中有些可能未必是蛇绿岩。(3)自1972年彭罗斯会议以来,蛇绿岩研究发展到现在,可能已经进入了一个关键时期。文中回顾了蛇绿岩的定义及其构造意义,指出1972年彭罗斯会议关于蛇绿岩的定义仍然是适用的。蛇绿岩可以概括为洋壳+地幔,这个洋壳来自板块扩张脊,是年轻的;这个地幔是大洋岩石圈地幔,也可能保留有古老岩石圈地幔的印记。蛇绿岩产于板块扩张脊,这是蛇绿岩构造含义的唯一解,蛇绿岩不存在多解性。(4)日喀则蛇绿岩的许多基本观点主要是法国学者提出来的,如关于岩床群的见解,慢速扩张的见解等。但是,上述见解是否都是对的是需要思考的。日喀则蛇绿岩具有得天独厚的条件,我们应当很好利用这个条件,努力把我们的研究做好,为全球蛇绿岩研究贡献我们的一份力量。     

甘孜－理塘蛇绿混杂岩带特征及其构造意义

本文系统总结了甘孜－理塘蛇绿混杂岩带的地质学、岩石学和地球化学特征。该蛇绿岩由变质橄榄岩、堆积岩、席状岩墙、枕状玄武岩与块状玄武岩和放射虫硅质岩组成。岩石地球化学特征表明，蛇绿岩形成于洋脊扩张环境。该蛇绿混杂岩带是义敦碰撞造山带大地构造相中的弧前混杂带相。     

准噶尔北部科克森套蛇绿岩中辉长岩年代学、岩石化学特征及地质意义

新疆西准噶尔北部科克森套蛇绿岩由辉长岩、辉橄岩、橄辉岩、辉石岩、蛇纹岩、玄武岩、硅质岩、含放射虫硅质板岩及片岩、片麻岩组成。辉长岩化学特征表现为富Al_2O_3、CaO、MgO,贫K_2O、TiO_2特点,与岛弧玄武岩相似。稀土元素与E-MORB特征基本一致,反映岩浆来源于富集地幔。微量元素具大离子亲石元素Rb,Th,K,Sr相对富集,高场强元素Nb,Ta,Ti相对亏损特征,显示与俯冲带流体交代有关。辉长岩锆石年龄(405±4) Ma,代表洋壳形成年代。在构造环境上,科克森套蛇绿混杂岩显示富集洋脊玄武岩特征,形成于岛弧环境,与岛弧消减带扩张环境相一致,因此,科克森套蛇绿混杂岩应形成于早泥盆世。从时间、空间分布及构造环境上,科克森套蛇绿岩与库尔提蛇绿岩、沙尔布拉克蛇绿岩及布尔根蛇绿岩具相似性,为早泥盆世古亚洲洋在准噶尔北缘向西伯利亚板块俯冲所形成的沟-弧-盆体系下的弧后系统,与相邻哈萨克斯坦斋桑蛇绿岩带、蒙古比基蛇绿岩带共同构成西伯利亚与准噶尔板块间的缝合带。     

准噶尔—天山—北山蛇绿岩:对中亚造山带西南缘洋陆格局演化的制约

准噶尔、天山和北山52个蛇绿岩的地质特征、地球化学性质和同位素年代学资料系统集成研究表明它们可以分为14条蛇绿(混杂)岩带。绝大多数蛇绿岩呈"岩块+基质"的混杂岩型式沿重要断裂带(构造线)线状分布,少数蛇绿岩以构造岩片叠置方式面状产出。混杂岩的基质有蛇纹岩(碳酸盐化蛇纹岩)和糜棱岩化细碎屑岩两类,岩块既有地幔橄榄岩、基性杂岩和基性火山岩等蛇绿岩组分,也有其它非蛇绿岩组分岩石。堆晶岩出露局限,典型席状岩墙群没有发育。这些蛇绿岩可归类为SSZ(Supra-Subduction Zone)和MORB(Mid-Ocean Ridge)两种类型,前者玄武岩具大离子亲石元素(LILE)富集和高场强元素(HFS)亏损特征,后者不显示该特点;洋岛玄武岩(OIB)既可出现在SSZ型蛇绿混杂岩中,也可为MORB型的组成部分;SSZ型蛇绿混杂岩辉长岩和玄武岩比MORB型具有相对更富集的Sr-Nd同位素组成,但部分形成于弧后(间)盆地的SSZ型蛇绿岩与MORB型一致,具有近亏损地幔的Sr-Nd同位素组成。已确认的最老蛇绿岩为西准噶尔572 Ma玛依勒,次之为北山542~527 Ma月牙山—洗肠井和西准噶尔531 Ma唐巴勒,最年轻蛇绿岩为325 Ma北天山巴音沟和321 Ma北山芨芨台子。根据蛇绿岩证据,结合近年来中亚造山带古地磁、岩浆岩、高压—超高压变质岩和构造地质方面的进展,可以推断埃迪卡拉纪末期—早寒武世,古亚洲洋已达到一定规模宽度,发育洋岛和洋内弧;早古生代时期,多岛洋格局发育至鼎盛期,一系列弧地体分别归属哈萨克斯坦微陆块周缘的科克切塔夫—天山—北山线性弧、成吉思弧、巴尔喀什—西准噶尔弧体系和西伯利亚南部大陆边缘弧体系;晚古生代时期,古亚洲洋于石炭纪末期闭合,增生杂岩和弧地体组成哈萨克斯坦拼贴体系和蒙古拼贴体系两个巨型山弯构造。     

甘肃北山早古生代蛇绿岩带的特征及演化

板块构造学说问世以来,地质学有了突破性进展。现代大洋岩石与大陆蛇绿岩之间明显的相似性,使人们把蛇绿岩视为消失大洋在大陆造山带中的残留标志。笔者综合有关蛇绿岩的研究成果,在我国北山首次确定了早古生代的蛇绿岩带,并对其发展演化做了研究     

Geologie und Bau des Sithonia-Ophioliths (Chalkidiki,NE-Griechenland): Anmerkungen zur Bildung ozeanischer Krusten

The Upper Jurassic Sithonia ophiolite of Chalkidiki (NE Greece) provides the opportunity to study the processes of the formation of fossil oceanic crusts in detail. This ophiolite consists from top to base of:

1. an over 900 m thick succession of shallow-water sediments frequently interlayered with basic volcanics;
2. an about 700 m thick basaltic layer which predominantly consists of hyaloclastics;
3. an excellently developed sheeted dyke complex which is at least 1.2 km thick. It is the main scope of this study.

The sheeted dyke complex consists entirely of dykes. They have intruded each other preferably along their margins. Two groups of dykes may be distinguished. The first group comprises those dykes which were obviously formed within the active spreading zone. These dykes make up the structure of the sheeted complex. They are in average 3.9 m thick and do not display a clear polarity of their chilled margins. The dykes of the second group were formed later, i.e. off-ridge. They are up to 0.8 m thick and almost always symmetrically chilled. The general strike of the dykes is N 54° E. This direction is almost perpendicular to the major tectonic units of Chalkidiki. The geometrical relations between the dykes can be best explained by formation at an oscillatory spreading axis. Available geological and geochemical data suggest a low to very low spreading rate. A periodic process of dyke injection is recognized. The dyke injection periods are of variable duration. This together with the restricted and variable magmatic differentiation within the different periods points towards a nonsteady state magma chamber beneath the spreading axis. The off-ridge dykes impart valuable information as regards the spreading direction and the relative position of the paleoridge. Some ideas about the spreading rate may also be obtained from these dykes. The shallow-water conditions during the sedimentation may be explained as due to the tectonic uplift of the Upper Jurassic oceanic crust possibly along a transcurrent fault. This interpretation is supported by other geological observations.     

Sheeted dykes in Kandra ophiolite complex,Nellore schist belt,Andhra Pradesh — Vestiges of Precambrian oceanic crust

Extensive field and petrological studies carried out in Kandra ophiolite complex (KOC) in the southern part of Nellore schist belt (NSB) revealed the existence of sheeted dykes in Kandra- Kondakuru-Gollapalli section. The sheeted dykes occur in the northern part of the complex and compositionally vary from medium-grained dolerites showing typical sub-ophitic texture to diabase dykes that are extremely fine grained aphanitic to fine-grained cryptocrystalline parallel basic dykes (varying in width from 4 cm to 1.25 m). These dykes show chilled margins on either side with the host dykes into which these are intruded. Veins of oceanic plagiogranite (0.5 × 5 m) are noticed in a major sheeted dyke. Occurrence of oceanic plagiogranite as ovoid / semicircular patches of 6 cm diameter resembling “immiscible droplets” within basic dykes is also noticed. The southern part of the complex is made of a major NW-SE trending cumulus gabbro that grades into olivine gabbronorite in its eastern part. The southern gabbros represent the plutonic component and form the deeper part of the complex. In this paper an attempt has been made to present the field, petrographic and mineral chemistry account of various lithounits that constitute the Kandra ophiolite complex in a succinct manner.     

丁青蛇绿岩新知

1982年7—8月间,我们在青藏高原东部横断山地区综合科学考察工作中,对丁青一带的蛇绿岩进行了初步调查,发现了席状岩墙群和一个比较连续的蛇绿岩剖面。 丁青蛇绿岩位于班公湖—东巧—怒江蛇绿岩带的中段。近几年来,不少人对这个带进行了研究。由于构造破坏,蛇绿岩强烈肢解,迄今为止,还未报道过有如丁青那样连续的蛇绿岩剖面。丁青蛇绿岩的新发现,对于青藏高原第二条缝合线内蛇绿岩的性质以及古特提斯海演化历史的研究提供了新的资料。 席状岩墙群出露于西藏丁青县沙贡区海拔5120米的日隆山的北坡。岩墙走向NE—NNE,倾角很陡,倾向sE或NW。岩墙宽约4米至20厘米,有的仅数厘米。主要由辉绿岩组成,中粒至细粒,有的为隐晶质的。     

Geochronology and Geochemistry of the Middle Proterozoic Aoyougou Ophiolite in the North Qilian Mountains,Northwestern China

The Aoyougou ophiolite lies in an early Palaeozoic orogenic belt of the western North Qilian Mountains, near the Aoyougou valley in Gansu Province, northwestern China. It consists of serpentinite, a cumulate sequence of gabbro and diorite, pillow and massive lavas, diabase and chert. Ages of 1840±2 Ma, 1783±2 Ma and 1784±2 Ma on three zircons from diabase, indicate an early Middle Proterozoic age. The diabases and basalts show light rare-earth element enrichment and have relatively high TiO2 contents, characteristic of ocean island basalts. All of the lavas have low MgO, Cr, Ni contents and Mg numbers indicating a more evolved character. They are believed to have been derived from a more mafic parental magma by fractionation of olivine, Cr-spinel and minor plagioclase. Based on the lava geochemistry and regional geology, the Aoyougou ophiolite was probably believed to have formed at a spreading centre in a small marginal basin. Subduction of the newly formed oceanic lithosphere in the Middle Proteroz     

西藏南部日喀则地区蛇绿岩地质

近年来,对雅鲁藏布蛇绿岩带的研究引起了国内外学者的广泛兴趣,因为它不仅对了解中生代以来特提斯海的演变,而且对阐明青藏高原地质发展历史都是十分重要的。虽然,这条带内大规模超基性岩体的分布早已被发现,有些岩体已作过很好的研究。但是,整个蛇绿岩组合的综合性研究还刚开始。最近一些作者根据野外路线调查,对这条蛇绿岩带作了初步的论述。但由于缺乏对蛇绿岩比较系统的填图工作,关于它的分布、组成、层序、形成、侵位及其演化历史还有许多重要情况不十分清楚。     

Propagating rift tectonics of a Caledonian marginal basin: Multi-stage seafloor spreading history of the Solund-Stavfjord ophiolite in western Norway

The Late Ordovician Solund-Stavfjord ophiolite in western Norway represents a remnant of the Iapetus oceanic lithosphere that developed in a Caledonian marginal basin. The ophiolite contains three structural domains that display distinctively different crustal architecture that reflects the mode and nature of magmatic and tectonic processes operated during the multi-stage seafloor spreading evolution of this marginal basin. Domain I includes, from top to bottom, an extensive extrusive sequence, a transition zone consisting of dike swarms with screens of pillow breccias, a sheeted dike complex, and plutonic rocks composed mainly of isotropic gabbro and microgabbro. Extrusive rocks include pillow lavas, pillow breccias, and massive sheet flows and are locally sheared and mineralized, containing epidosites, sulfide-sulfate deposits, Fe-oxides, and anhydrite veins, reminiscent of hydrothermal alteration zones on the seafloor along modern mid-ocean ridges. A fossil lava lake in the northern part of the ophiolite consists of a >65-m-thick volcanic sequence composed of a number of separate massive lava units interlayered with pillow lavas and pillow breccia horizons. The NE-trending sheeted dike complex contains multiple intrusions of metabasaltic dikes with one- and two-sided chilled margins and displays a network of both dike-parallel normal and dike-perpendicular oblique-slip faults of oceanic origin. The dike-gabbro boundary is mutually intrusive and represents the root zone of the sheeted dike complex. The internal architecture and rock types of Domain I are analogous to those of intermediate-spreading oceanic crust at modern mid-ocean ridge environments. The ophiolitic units in Domain II include mainly sheeted dikes and plutonic rocks with a general NW structural grain and are commonly faulted against each other, although primary intrusive relations between the sheeted dikes and the gabbros are locally well preserved. The exposures of this domain occur only in the northern and southern parts of the ophiolite complex and are separated by the ENE-trending Domain III, in which isotropic to pegmatitic gabbros and dike swarms are plastically deformed along ENE-striking sinistral shear zones. These shear zones, which locally include fault slivers of serpentinite intrusions, are crosscut by N20°E-striking undeformed basaltic dike swarms that contain xenoliths of gabbroic material. The NW-trending sheeted dike complex in the northern part of Domain II curves into an ENE orientation approaching Domain III in the south. The anomalous nature of deformed crust in Domain III is interpreted to have developed within an oceanic fracture zone or transform fault boundary.REE chemistry of representative extrusive and dike rocks from all three domains indicates N- to E-MORB affinities of their magmas with high Th/Ta ratios that are characteristic of subduction zone environments. The magmatic evolution of Domain I encompasses closed-system fractional crystallization of high-Mg basaltic magmas in small ephemeral chambers, which gradually interconnected to form large chambers in which mixing of primary magmas with more evolved and fractionated magma caused resetting of magma compositions through time. The compositional range from high-Mg basalts to ferrobasalts within Domain I is reminiscent of modern propagating rift basalts. We interpret the NE-trending Domain I as a remnant of an intermediate-spread rift system that propagated northeastwards (in present coordinate system) into a pre-existing oceanic crust, which was developed along the NW-trending doomed rift (Domain II) in the marginal basin. The N20°E dikes laterally intruding into the anomalous oceanic crust in Domain III represent the tip of the rift propagator. The inferred propagating rift tectonics of the Solund-Stavfjord ophiolite is similar to the evolutionary history of the modern Lau back-arc basin in the SW Pacific and suggests a complex magmatic evolution of the Caledonian marginal basin via multi-stage seafloor spreading tectonics.     

西昆仑库地蛇绿岩地质、地球化学及其成因研究

西昆仑库地蛇绿混杂岩由方辉橄榄岩和纯橄榄岩等地幔变质橄榄岩、豆荚状铬铁矿、堆晶橄榄岩、堆晶辉石岩和辉长岩、辉绿岩墙、块状和枕状玄武岩等组成。强亏损方辉橄榄岩为主的地幔岩组合,二辉石的低Al含量和铬尖晶石的高Cr^#,以及岩石的富Mg、Ni和贫Al、Ca特征一致表明地幔橄榄岩类是经较高程度部分熔融后的地幔残余,与消减带之上蛇绿岩中的同类岩石相近。岩石富Rb、Ba、U、Th、LREE,说明地幔残余岩石受到了来自消减带的洋壳重熔组分的混染。堆晶岩以辉石岩和辉长岩为主,可能属PPG系列,指示岩浆是在消减带环境和含水条件下熔融的。辉长岩为低Ti蛇绿岩型,代表洋内弧后盆地早期环境或弧前环境。辉绿岩和玄武岩为洋中脊拉斑玄武岩和岛弧拉斑玄武岩的过渡类型;玄武岩和辉绿岩相比富Ba、Th、LREE,贫Ta,指示玄武岩较辉绿岩更多地受到来自消减带洋壳重熔组分的影响。库地蛇绿岩形成时的古构造环境是消减带之上的弧间或弧后盆地。     

The origin and emplacement of the Lajishankou ophiolite complex in the South Qilian belt: evidences from geological mapping

Many ophiolite complexes like those of Oman and New Caledonia represent fragments of ancient oceanic crust and upper mantle generated at supra‐subduction zone environments and have been obducted onto the adjacent rifted continental margin together with the accretionary complexes and intra‐oceanic arcs. The Lajishan ophiolite complexes in the Qilian orogenic belt along the NE edge of the Tibet‐Qinghai Plateau are one of several ophiolites situated to the south of the Central Qilian block. Our geological mapping and petrological investigations suggest that the Lajishankou ophiolite complex consists of serpentinite, wehrlite, pyroxenite, gabbro, dolerite, and pillow and massive basalts that occur in a series of elongate fault‐bounded slices. An accretionary complex composed mainly of basalt, radiolarian chert, sandstone, mudstone, and mélange lies structurally beneath the ophiolite complex. The Lajishankou ophiolite complex and accretionary complex were emplaced onto the Qingshipo Formation of the Central Qilian block which shows features typical of turbidites deposited in a deep‐water environment of passive continental margin. Our geochemical and geochronological studies indicate that the mafic rocks in the Lajishankou ophiolite complex can be categorized into three distinct groups: massive island arc tholeiites, 509 Ma back‐arc dolerite dykes, and 491 Ma pillow basaltic and dolerite slices that are of seamount origin in a back‐arc basin. The ophiolite and accretionary complex constitute a Cambrian‐early Ordovician trench‐arc system within the South Qilian belt during the early Paleozoic southward subduction of the South Qilian Ocean prior to Early Ordovician obduction of this system onto the Central Qilian block.     

北补连蛇绿岩的特征,形成环境及其构造意义

文中总结了北祁连蛇绿岩的特征，指出北祁连蛇绿岩大多具有ＭＯＲＢ的性质，有玻安岩产生，形成在弧后和岛弧环境，北祁连蛇绿岩大多侵位在岛弧增生楔或活动陆缘地体之上，蛇绿岩属于科迪勒拉型，早古生代的北祁连造山带属于科迪勒拉型造山带，部分蛇绿岩之上整合产出一套沉积一火山岩系，称为蛇绿岩的上覆岩系，指出蛇绿岩及其上覆岩系的枕状熔岩分别来自不同的源区，具有不同的构造意义，还讨论了北祁连早古生代板块构造格局，认为