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1.
雅鲁藏布江缝合带西段出露东波和普兰等多个大型的超镁铁岩体，其成因还存在争议。为此我们近年来对东波蛇绿岩开展了地表填图并实施了一口1002m的科学钻探DSD-1。研究显示具有"厚幔极薄壳"特征的东波蛇绿岩记录了多期岩浆事件：（1）~137Ma的OIB型玄武岩和138~144Ma的OIB型辉绿岩和辉长岩，以及普遍出露熔融程度达30%以上的亏损型方辉橄榄岩，反映了早白垩世初期古洋盆受到地幔柱活动影响；（2）129Ma的薄壳均质辉长岩（I型）、128Ma的辉长岩脉（Ⅱ型）和科钻岩芯中厚18m辉绿岩（Ⅲ型）的地球化学成分均与西南印度洋洋脊玄武岩类似，它们是在慢速-超慢速扩张脊附近大洋核杂岩侵位过程中形成的；（3）地表辉绿岩脉（Ⅳ型）的SIMS和SHRIMP锆石U-Pb年龄为121~123Ma，全岩地球化学具有异常低的REE、HFSE含量及明显的Th、Nb、Zr、Hf负异常，类似于Albanide-Hellenide造山带蛇绿岩中的无壳源物质混染的中钛玄武岩，指示辉绿岩脉形成于洋内初始俯冲环境。总的来说，东波蛇绿岩记录了早白垩世地幔柱影响的超慢速扩张和初始洋内俯冲过程。 相似文献
2.
西藏雅鲁藏布江缝合带西段东波蛇绿岩的构造背景特征 总被引：2，自引：0，他引：2
西藏东波蛇绿岩位于雅鲁藏布江缝合带西段,由地幔橄榄岩、辉石岩和辉长岩等组成。地幔橄榄岩主要为方辉橄榄岩、纯橄岩和少量二辉橄榄岩。岩体的边界出露玄武岩和硅质岩等。地幔橄榄岩中有少量辉石岩和辉长岩的脉岩,宽约1 m,走向北西,与岩体的构造线方向基本一致。各岩相岩石地球化学研究结果表明,东波蛇绿岩的岩相存在较大的差异,玄武岩具有与洋岛玄武岩(OIB)相似的地球化学特征,而地幔橄榄岩中辉石岩、辉长岩脉与洋中脊玄武岩(MORB)相似,形成于洋中脊环境,并受后期俯冲流体作用的改造。东波岩体中二辉橄榄岩具有与深海地幔橄榄岩较一致的轻稀土亏损特征,而方辉橄榄岩和纯橄岩的地球化学特征显示出岩体形成于MOR环境,后受到SSZ环境的改造。东波蛇绿岩的岩石地球化学特征显示其洋中脊叠加洋岛的构造背景。 相似文献
3.
西藏雅鲁藏布江缝合带西段东波蛇绿岩中锆石U-Pb定年及地质意义 总被引：18，自引：15，他引：3
西藏东波蛇绿岩位于雅鲁藏布江缝合带西段,由地幔橄榄岩、辉石岩和辉长岩等组成.地幔橄榄岩主要为方辉橄榄岩、纯橄岩和少量二辉橄榄岩.地幔橄榄岩中有少量辉石岩和辉长岩的脉岩,宽约1m,走向北西与岩体的构造线方向基本一致.辉石岩由90％透辉石(Wo=48、En =46、Fs =6),少量的斜顽辉石(Wo=2、En=82、Fs=16),5％的斜长石(An =90)和透闪石组成.辉长岩主要由透辉石(Wo =47、En=36、Fs=17)、斜长石(An =47)及少量的镁角闪石组成,岩石成分以低K2O和P2O5含量(均＜0.1％)和亏损的LREE模式为特征,显示N-MORB岩石的特征.经LA-ICP-MS锆石U-Pb原位微区测定,获得辉石岩和辉长岩的年龄分别为130±0.5Ma、128±1.1Ma.首次给出了东波蛇绿岩年龄,代表了东波地区新特提斯洋海底扩张的时代. 相似文献
4.
舍马拉沟蛇绿岩位于班公湖-怒江缝合带西段改则地区,是改则蛇绿岩的重要组成部分。为确定该蛇绿岩构造属性及成因,进行了岩石学与全岩地球化学研究。该蛇绿岩中发现有地幔橄榄岩、辉长岩及辉绿岩等,其中辉长岩SiO2平均含量47.65%,Mg#平均值77.1,辉长岩稀土分布模式与地幔橄榄岩相似,具Eu正异常。辉绿岩SiO2平均含量50.52%,Mg#为50~56.4,辉绿岩各样品REE分布模式特征相似,∑REE为45.58×10-6~66.55×10-6,分布型式为平坦型。蛇绿岩具IAT型和MOR型岩石地球化学特征,可能形成于弧后盆地环境,是特提斯大洋岩石圈在俯冲过程中引发弧后次级扩张的产物。 相似文献
5.
皖南伏川蛇绿岩是江南造山带上出露最完整的蛇绿岩,主要由地幔橄榄岩、堆晶岩、枕状熔岩和少量硅质岩组成.地幔橄榄岩主要是方辉橄榄岩,具有U型的稀土元素配分模式,副矿物尖晶石的Cr#较高(54～60),堆晶岩组合为纯橄岩-易剥橄榄岩-辉长岩(DIG型),这些特征指示伏川蛇绿岩形成于俯冲带之上的构造环境,属SSZ型蛇绿岩.堆晶岩异剥橄榄岩的锆石SHRIMP U-Pb年龄为827±9 Ma(n=12,MSWD=1.4),侵入到方辉橄榄岩中的辉长岩岩脉的锆石SHRIMP U-Pb年龄为848±12 Ma(n=7,MSWD=1.9),说明扬子板块和华夏板块至少在848Ma之前就开始拼合,它们之间的古大洋在新元古代(～850 Ma)之前就已经俯冲削减. 相似文献
6.
雅鲁藏布江缝合带西段东波蛇绿岩OIB型玄武岩的厘定及其形成环境 总被引：9，自引：8，他引：1
雅鲁藏布江缝合带(YZSZ)西段分为两支,南带蛇绿岩的成因对整个缝合带的性质和构造背景的探讨起到十分关键作用,但由于地区偏远、交通不便,研究程度一直十分薄弱.本文报道了南带的东波蛇绿岩中洋岛型玄武岩及有关沉积岩的发现和成因探讨.东波蛇绿岩主要由地幔橄榄岩(方辉橄榄岩、含单辉方辉橄榄岩和透镜状纯橄岩)和上覆火山-沉积岩组成,未见堆晶岩和枕状熔岩等典型洋壳端元.火山-沉积岩盖层为一套稳定的海相层序,主要由硅质灰岩、红色硅质岩等沉积岩和玄武岩和玄武火山碎屑岩组成.OIB型玄武岩的特征表现为低SiO2和MgO,高TiO2、P2O5和(K2O+Na2O),富集Nb、Ta,亏损Th、K、Pb、Sr.微量元素和Sr、Nd、Pb同位素数据显示,该玄武质源区来自石榴石尖晶石二辉橄榄岩2％ ～ 5％的部分熔融.成分研究显示,硅质岩形成于大陆边缘环境,为洋岛或海山和大陆边缘物质在生物作用下形成的.以上证据表明,东波火山-沉积岩层序具有典型海山特征,与世界上典型的地幔柱型蛇绿岩可对比,属于地幔柱热点活动的产物.因此,可以认为,地幔柱热点在与冈瓦纳大陆北缘岩石圈地幔相互作用过程中,不但促使YZSZ西段南带(达巴-休古嘎布)特提斯洋盆打开,还可能与YZSZ蛇绿岩中普遍包含金刚石等异常地幔矿物群有直接的动力学关系. 相似文献
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日喀则蛇绿岩位于雅鲁藏布构造带中段,其成因和构造环境仍存在较大争议。日喀则蛇绿岩下部为蛇纹石化地幔橄榄岩,壳幔过渡带缺失超镁铁质堆晶岩。少量辉长岩脉呈块状或韵律结构并侵入到地幔橄榄岩和辉绿岩中。辉绿岩呈席状岩床侵入到地幔橄榄岩之上,且少量辉绿岩脉侵入到下覆的地幔橄榄岩中。通过野外关系和地球化学研究,日喀则辉长岩可能并不是洋壳中岩浆房原位结晶堆积而成,而是深部位置岩浆囊经过不同程度分异演化形成富晶粥岩浆并向上侵入的结果。而席状辉绿岩床则是基性岩浆沿着构造薄弱面顺层侵入的结果。拆离断层可能导致了岩石圈地幔抬升和剥露,进而引起下覆软流圈地幔减压熔融和岩浆上侵。日喀则辉长-辉绿岩形成于慢速扩张脊较小规模的岩浆供应和不连续的岩浆侵入。 相似文献
8.
雅鲁藏布蛇绿岩——事实与臆想 总被引：15，自引：12，他引：3
位于西藏南部的雅鲁藏布蛇绿岩在我国研究程度最高,在国际上也有较高的知名度。该蛇绿岩东西延伸约2000km,代表了印度和亚洲之间消失的新特提斯洋,是确定上述两大板块间缝合线存在的重要岩石学标志。本文根据作者近几年的野外考察,结合前人发表的资料发现,该蛇绿岩有如下方面的重要特点。(1)各蛇绿岩剖面均发育大规模的橄榄岩体,超镁铁岩的分布远远大于镁铁质岩石。这些超镁铁岩体尽管在岩性上以方辉橄榄岩为主,但出现大量二辉橄榄岩;(2)镁铁质堆晶辉长岩不发育;(3)不存在席状辉绿岩墙群,取而代之的是顺层侵入在橄榄岩中的辉长岩-辉绿岩岩席。部分情况下,辉绿岩还侵入到玄武岩之中;(4)蛇绿岩上部发育有一定厚度的玄武岩,但玄武岩与橄榄岩之间经常被辉绿岩席所占据,部分情况下玄武岩与橄榄岩直接接触。(5)地幔橄榄岩与镁铁质岩石在Sr-Nd同位素和形成时代上存在显著差别;(6)辉长岩与辉绿岩形成在120~130Ma的狭窄时间段内,并具有类似亏损地幔的地球化学特点。上述资料表明,雅鲁藏布蛇绿岩中的超镁铁岩和镁铁质岩形成于不同时代,且在成因上不具任何联系。根据这些资料,本文提出,该区蛇绿岩的地幔橄榄岩可能为大陆岩石圈地幔。早白垩世期间,北侧亚洲大陆南缘位置的岩石圈由于拉张而使深部岩石圈地幔物质向上剥露。随着岩石圈拆离和减薄的不断进行,软流圈地幔发生减压熔融,形成目前见到的玄武岩和辉长-辉绿岩席。在拉张作用的高峰期,早期亏损的大陆岩石圈地幔在经历交代作用后发生部分熔融形成少量玻安质熔体。因此,雅鲁藏布蛇绿岩并不能代表新特提斯大洋,它与经典的蛇绿岩定义相差甚远。考虑镁铁质岩石发育有限的特点,雅鲁藏布蛇绿岩代表了一种超慢速扩张的洋盆形成环境,其扩张速率甚至慢于目前广为人知的西Alps地区。根据全球蛇绿岩的情况,该蛇绿岩可被定义为日喀则型,是目前超慢速扩张洋盆的端元代表。 相似文献
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本文报道了雅鲁藏布江缝合带西段的东波蛇绿岩地幔橄榄岩中发现与罗布莎和普兰岩体相似的金刚石和特殊地幔矿物群。东波地幔橄榄岩体以方辉橄榄岩为主,含少量二辉橄榄岩和纯橄岩,辉石岩和辉长岩呈脉状产在方辉橄榄岩中。岩石地球化学特征表明东波岩体形成于MOR环境后受到SSZ环境的改造。通过重砂分选实验,在693 kg的地幔橄榄岩大样中发现了金刚石和碳硅石等30余种特殊矿物群,包括金刚石、自然铬、自然金、自然铁、自然硅、自然铜等自然元素矿物类;碳硅石等碳化物;铬尖晶石、金红石、铬铁矿、刚玉、黑钨矿、铌钽铁矿、磁铁矿、赤铁矿、方铁矿、锡石等氧化物;铁铬镍合金、镍铁合金、铜锌合金等合金互化物;辉钼矿、方铅矿、辉铋矿、黄铁矿、黄铜矿、毒砂和闪锌矿等硫化物;橄榄石、辉石、锆石、蓝晶石、白云母、蛇纹石、绿帘石等硅酸岩;萤石等氟化物。该矿物群与雅鲁藏布江缝合带的罗布莎和普兰两个岩体中发现的特殊矿物群非常类似,同时也为蛇绿岩型金刚石这一新类型提供了佐证。 相似文献
10.
北祁连玉石沟蛇绿岩形成于晚震旦世的SHRIMP年龄证据 总被引：45，自引：5，他引：45
玉石沟蛇绿岩位于青藏高原东北缘的北祁连山中部 ,由地幔橄榄岩、堆晶辉长岩、辉绿岩、枕状熔岩以及夹杂在其中的硅质岩组成。地幔橄榄岩主要是方辉橄榄岩 ,其主要氧化物成分较为单一 ,具 L REE富集、Eu亏损的 U形 REE配分模式 ,亏损强不相容元素 ;枕状熔岩具典型 MORB特征 ,在构造判别图解上位于 MORB和 IAT区域 ,指示蛇绿岩可能形成于类似于洋中脊的构造环境 ,并受到火山弧岩浆作用的影响。堆晶辉长岩具明显的 Eu正异常 ,其锆石离子探针 (SHRIMP) 2 0 6 Pb/2 38U加权平均年龄为 5 5 0± 17Ma,Th/U值为 0 .5 3～ 1.85 ,大于0 .2 3,为岩浆成因锆石 ,其年龄代表辉长岩的成岩时代 ,推断玉石沟蛇绿岩形成于晚震旦世。 相似文献
11.
Important mafic–ultramafic masses have been located for the first time in the intersection area between the Keraf Shear Zone and the Nakasib Suture Zone of the Nubian Shield. The masses, comprising most of the members of the ophiolite suite, are Sotrebab and Qurun complexes east of the Nile, and Fadllab complex west of the Nile. The new mafic–ultramafic masses are located on the same trend of the ophiolitic masses decorating the Nakasib Suture. A typical complete ophiolite sequence has not been observed in these complexes, nevertheless, the mafic–ultramafic rocks comprise basal unit of serpentinite and talc chlorite schists overlain by a thick cumulate facies of peridotites, pyroxenites and layered gabbros overlain by basaltic pillow lavas with dolerite dykes and screens of massive gabbros. Associated with pillow lavas are thin layers of carbonates and chert. The best section of cumulate mafic–ultramafic units has been observed in Jebel Qurun and El Fadlab complexes, comprising peridotites, pyroxenites and layered gabbros. Dolerite dykes and screens of massive gabbros have been observed with basaltic pillow lava sections in Wadi Dar Tawaiy. The basal ultramafic units of the complexes have been fully or partly retrograded to chlorite magnetite schist and talc to talc-carbonate rocks (listowenites), especially in the Jebel Qurun and Sotrebab complexes. Petrographically, the gabbros (layered and massive) and the basaltic pillow lavas show mineral assemblages of epidote amphibolite facies. The mafic members from the three complexes show a clear tholeiitic trend and oceanic floor affinity. The pillow lavas plot in the field of oceanic floor basalt, namely in the back arc field. Primitive mantle normalized spider diagram of the pillow lavas reveals a closer correspondence to Enrich-Mid-Oceanic Ridge Basalt (E-MORB) type, which is confirmed by the flat chondrite normalized Rare Earth Elements (REE) pattern. Field, petrographical and geochemical evidence supports ophiolitic origin of the three complexes. The newly discovered ophiolitic complexes mark the western continuation of the Nakasib Suture Zone. 相似文献
12.
乌兰敖包基性-超基性岩位于阿拉善北缘兴蒙造山带,由方辉橄榄岩、辉绿岩、辉长岩组成。地球化学分析表明:蛇纹石化橄榄岩为地幔橄榄岩,辉绿岩和辉长岩为拉斑玄武岩系列岩石,均具有与N-MORB相似的微量元素特征,但区别于N-MORB,3种岩石共同组成了蛇绿混杂岩。矿物学分析表明蛇纹石化橄榄岩中橄榄石为地幔橄榄岩中镁橄榄石(Fo=91.10~91.81),铬铁矿为铬尖晶石,具有高的Cr~#和Mg~#值分别为61.04~64.44、50.40~56.37)。单斜辉石出现在方辉橄榄岩、辉长岩及辉绿岩中,而斜方辉石只出现在方辉橄榄岩中,其中方辉橄榄岩中单斜辉石为顽透辉石,辉长岩中为普通辉石,而辉长岩中为次透辉石、贫钙普通辉石、普通辉石,斜方辉石均为斜顽辉石。辉长岩U-Pb年龄为344.5±1.5 Ma,表明该蛇绿混杂岩形成于早石炭世。地球化学及矿物学特征表明乌兰敖包蛇绿岩形成于俯冲早期的弧前环境中,属于SSZ型蛇绿岩。蛇绿混杂岩成因提供铬铁矿形成的有利条件,因此应围绕铬铁矿进行找矿工作。 相似文献
13.
The SW Antalya Complex is an assemblage of Mesozoic carbonate platform, margin and ophiolitic rocks which record the formation and tectonic emplacement of a small Mesozoic ocean basin. The late Cretaceous ophiolitic rocks are located at two localities, namely the relatively intact Tekirova ophiolite to the east of Kemer zone and the dismembered Gödene ophiolite to the west of Kemer zone. The Tekirova (Antalya) ophiolite comprises harzburgitic tectonites, ultramafic to mafic cumulates, isotropic gabbros and sheeted dikes. Numerous isolated dikes, ranging in thickness from 5 cm to 10 m, intruded the crustal rocks at different structural levels. The isotropic gabbros are represented by gabbro, diorite and quartz diorite rocks with granular to ophitic–subophitic textures. The isolated dikes are characterized by dolerite, diabase and microdiorite with ophitic, intersertal and microgranular textures. These rocks exhibit tholeiitic to alkaline compositions. New geochemical data presented in this paper from the isolated dikes and isotropic gabbros suggest that there are three main types of parental basic magmas that form the oceanic crustal rocks of the Tekirova (Antalya) ophiolite. These are (1) IAT series which can be referred to the Group I isolated dikes and isotropic gabbros; (2) low-Ti boninitic series characterized by the Group II isolated dike and isotropic gabbros; and (3) OIB-type including the Group III isotropic gabbros. The geochemical evidence suggests that the crustal rocks of the Tekirova (Antalya) ophiolite were generated from a progressive source depletion from island arc tholeiites (IAT) to boninites. Therefore, a fore-arc tectonic setting seems likely for the generation of the crustal rocks from the Tekirova (Antalya) ophiolite in the southern branch of Neotethys during the Late Cretaceous. The OIB-type alkaline isotropic gabbros are thought to have resulted from either (1) a late-stage magmatic activity fed by melts that originated within an asthenospheric window due to slab break-off or (2) subduction of a ridge system which generated OIB source across the asthenospheric window that has been no influence of fluids from the subducted slab into the overlying mantle wedge, shortly before the emplacement of the Tekirova (Antalya) ophiolite onto the Tauride platform. 相似文献
14.
The West Junggar, located in the southernmost part of the Central Asian Orogenic Belt (CAOB), is a key region for understanding the Paleozoic evolution of the CAOB. Issues of the timing of initial subduction and tectonic unit connections in northern West Junggar still remain controversial. In this study, we report a new ophiolitic mélange named the E'min ophiolitic mélange in northern West Junggar. The tectonic blocks in the E'min ophiolitic mélange are mainly composed of serpentinized peridotite, serpentinite, gabbros, pillow basalts, and cherts, with a matrix consisting of highly deformed serpentinites. A gabbro exhibits a zircon SHRIMP U-Pb age of 476 ± 2 Ma, and the zircon grains have δ18O values similar to those of mantle zircons. Those basalt samples display depletions of light rare earth element (REE) relative to heavy REEs. They exhibit weak enrichment of Ba and Th, and moderate depletion of Nb and Ta. The basalts display similar geochemical characteristics to that of fore–arc basalts in the present-day fore–arc setting. The gabbros exhibit high MgO and compatible element contents, but low TiO2, total REE and high field strength element (HFSE) contents. They exhibit light REE depletion, enrichment in large-ion lithophile elements, and depletion of HFSEs. The boninite-like geochemical patterns of the gabbros indicate that they were formed in a subduction-related environment, and were derived from an extremely depleted mantle source infiltrated by subduction-derived fluids and/or melts. The E'min ophiolitic mélange has a geochemical make-up similar to those of suprasubduction-zone (SSZ)-type ophiolites formed in a forearc setting. Hence, we propose that the E'min ophiolitic mélange formed in a forearc setting and may represent the initial subduction in northern West Junggar. Based on geochronological data, we propose that the E'min ophiolite, together with the Kujibai, Hoboksar and Hongguleleng ophiolites, formed during a similar period and comprise a huge E–W trending ophiolitic belt. 相似文献
15.
《International Geology Review》2012,54(1):66-87
The Late Cretaceous Alihoca ophiolite in the Inner Tauride suture zone (ITSZ) of South-Central Turkey represents part of a single ophiolitic thrust sheet that originated from the Inner Tauride ocean. The ophiolite contains upper mantle peridotites, cumulate wehrlites, layered-to-isotropic gabbros, and microgabbroic-to-doleritic dikes. An ophiolitic mélange beneath the Alihoca ophiolite includes blocks of limestone, peridotite, dolerite, basalt, and deep-sea sedimentary rocks (radiolarite, chert) in a matrix comprising sheared serpentinite and mudstone. Isotropic gabbro and dolerite dike rocks show enrichment in Sr, K, Rb, Ba, and Th (LILE) and depletion of Ta, Nb, Zr, Ti, and Y (HFSE), indicating an island arc tholeiite (IAT) affinity. Relatively younger dolerite rocks display low TiO2 (<0.5 wt.%) contents, concave REE profiles with low HREE concentrations, and high LREE values, typical of boninitic affinities. The Alihoca ophiolite, hence, displays an IAT to boninitic geochemical progression in its magmatic evolution, reminiscent of many other Tethyan ophiolites in the region. It represents the remnant of a forearc oceanic crust, which developed during the early stages of subduction within the Inner Tauride ocean. Volcanic, volcano-sedimentary, and sedimentary rocks of the Uluk??la–Çamard? basin north of the ITSZ disconformably overlie the mafic-ultramafic rocks of the Alihoca ophiolite. Pillowed and massive lavas of the latest Cretaceous–Palaeocene Uluk??la Formation have alkaline basalt-to-basaltic andesite compositions, displaying relatively enriched LILE and LREE patterns with negative Nb and Ta anomalies. These geochemical features suggest that magmas of the Uluk??la–Çamard? volcanic rocks formed from partial melting of a metasomatized lithospheric mantle. This melting event was triggered by the influx of asthenospheric heat through a slab breakoff-induced window in the downgoing Tethyan oceanic lithosphere. 相似文献
16.
Petrology,geochemistry and geochronology of the Zhongcang ophiolite,northern Tibet: implications for the evolution of the Bangong-Nujiang Ocean 总被引：3，自引：0，他引：3
Ophiolites are widespread along the Bangong-Nujiang suture zone, northern Tibet. However, it is still debated on the formation ages and tectonic evolution process of these ophiolites. The Zhongcang ophiolite is a typical ophiolite in the western part of the Bangong-Nujiang suture zone. It is composed of serpentinized peridotite, cumulate and isotropic gabbros, massive and pillow basalts, basaltic volcanic breccia, and minor red chert. Zircon SHRIMP Ue Pb dating for the isotropic gabbro yielded weighted mean age of 163.4 ± 1.8 Ma. Positive zircon ε Hf(t) values(+15.0 to +20.2) and mantle-like σ~(18)O values(5.29 ±0.21)% indicate that the isotropic gabbros were derived from a long-term depleted mantle source. The isotropic gabbros have normal mid-ocean ridge basalt(N-MORB) like immobile element patterns with high Mg O, low TiO_2 and moderate rare earth element(REE) abundances, and negative Nb,Ti, Zr and Hf anomalies. Basalts show typical oceanic island basalt(OIB) geochemical features, and they are similar to those of OIB-type rocks of the Early Cretaceous Zhongcang oceanic plateau within the Bangong-Nujiang Ocean. Together with these data, we suggest that the Zhongcang ophiolite was probably formed by the subduction of the Bangong-Nujiang Ocean during the Middle Jurassic. The subduction of the Bangong-Nujiang Tethyan Ocean could begin in the Earlye Middle Jurassic and continue to the Early Cretaceous, and finally continental collision between the Lhasa and Qiangtang terranes at the west Bangong-Nujiang suture zone probably has taken place later than the Early Cretaceous(ca. 110 Ma). 相似文献
17.
阿民乌素地幔橄榄岩属芨芨台子-小黄山蛇绿岩带一部分,该构造带南北两侧地质体无明显差异,不具分界断裂的构造特征。本文对阿民乌素地幔橄榄岩与月牙山地幔橄榄岩进行岩石化学、地球化学对比分析,为芨芨台子-小黄山蛇绿岩构造属性提供新依据,并对阿民乌素蛇绿岩成矿潜力进行分析研究。笔者所在团队在地幔橄榄岩上部的辉长岩中获得LA-ICP-MS锆石U-Pb同位素年龄值为462.5±3.2 Ma,属中奥陶世。其上发育奥陶纪-志留纪公婆泉组岛弧拉斑玄武岩。该期地幔橄榄岩轻重稀土之比LR/HR＝1.63~3.68, (La/Sm)N＝1.70~6.92,(Gd/Yb)N＝0.36~0.52,表明岩石轻稀土略富集,稀土配分曲线呈不规则“U”型,估算其为原始地幔橄榄岩经过10%~20%部分熔融的残留物。原始地幔标准化蛛网图富集高场强元素U、Zr、Hf、Yb和大离子亲石元素Rb、Sr,亏损高场强元素Nb、Ti和大离子亲石元素Ba。与月牙山地幔橄榄岩标准化蛛网图对比,最大区别在于阿民乌素地幔橄榄岩明显亏损高场强元素Ti。初步研究认为阿民乌素地幔橄榄岩属SSZ型、高压型蛇绿岩,是岛弧裂谷的产物。该橄榄岩具有形成大型铬铁矿的成矿构造背景,是寻找蛇绿岩型铬铁矿的有利部位。 相似文献
18.
The Alxa region, located in the southernmost part of Central Asian Orogenic Belt, is a key region for understanding the tectonic processes associated with the closure of the Paleo-Asian Ocean. Issues of late Paleozoic tectonic settings and tectonic unit divisions of the Alxa region still remain controversial. In this study, we report a new ophiolitic mélange named the Tepai ophiolitic mélange in the northern Alxa region, northwest of Alxa Youqi. The tectonic blocks in the Tepai ophiolitic mélange are mainly composed of serpentinized peridotites, serpentinites, mylonitized gabbros, gabbros, basalts, and quartzites, with a matrix comprising highly deformed clastic rocks. A gabbro exhibits a zircon LA-ICP-MS Ue Pb age of278.4 ± 3.3 Ma. Gabbros exhibit high Mg O and compatible element contents, but extremely low TiO_2,totally rare earth element and high field strength element contents. These rocks exhibit light rare earth element depleted patterns, and display enriched in large-ion lithophile elements and depleted in high field strength elements. Boninite-like geochemical data show that they were formed in a subductionrelated environment, and derived from an extremely depleted mantle source infiltrated by subduction-derived fluids and/or melts. The Tepai ophiolitic mélange exhibits similar zircon U-Pb-O isotopic compositions and whole-rock geochemical characteristics to those of the Quagan Qulu ophiolite.Therefore, we propose that the Tepai ophiolitic mélange may have been the western continuation of the Quagan Qulu ophiolite. Our new finding proves the final closure of the Paleo-Asian Ocean might have taken place later than the early Permian. 相似文献
19.
Metamorphosed black shale is an essential component of the Early Proterozoic Outokumpu rock assemblage, together with serpentinite, calc-silicate rock and quartz rock. This rock assemblage, hosting the major Cu-Co-Zn deposits of Outokumpu and considered ophiolitic in origin, has also been encountered to the northwest in the Kainuu schist belt. The rift basin encompassing the two areas was intruded by ophiolite complexes 1.96–1.97 billion years ago. Remnants of ultramafites are met as serpentinite and talc-carbonate rock lenses bounded by faults along the western margin of the Kainuu schist belt. The black schist formations range in thickness from tens of metres to 400 m. Metal-rich layers occur close to the serpentinite bodies. The most extensive formations of metal-rich black schist (300 Mt, 0.26% Ni, 0.14% Cu, 0.53% Zn) have been encountered at Talvivaara. The lithological, mineralogical and geochemical results indicate a genetic link between the Jormua, Talvivaara, Alanen and Pappilanmäki prospects in the Kainuu schist belt and the Outokumpu rock assemblage. 相似文献
20.
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。 相似文献