甘肃景泰县老虎山地区蛇绿岩及其上覆岩系中枕状熔岩的地球化学特征   总被引：10，自引：3，他引：10  

张旗  王岳明 《岩石学报》1997,13(1):92-99

甘肃景泰县老虎山地区蛇绿岩之上覆盖着一套镁铁质的喷出岩和沉积岩组合，位于蛇绿岩的枕状熔岩之上，不是蛇绿岩的成员，为蛇绿岩的上覆岩系。蛇绿岩的枕状熔岩具Ｎ－ＭＯＲＢ的特征，而其上覆岩系中的枕状熔岩类似Ｅ－ＭＯＲＢ。前者来自扩张脊的下部岩浆房；后者推测源于扩张脊之外的岩浆房，也是软流圈地幔中等至高程度部分熔融的产物，不过，可能有少量来自下地幔的物质的加入  相似文献   

东秦岭松树沟超镁铁岩侵位机制及其构造演化   总被引：3，自引：0，他引：3  

董云鹏  周鼎武  张国伟 《地质科学》1997,(2):173

 东秦岭松树沟蛇绿岩主要由镁铁质-超镁铁质岩石组成。镁铁质岩类的Sm-Nd全岩等时年龄为1030±46(2δ)Ma,ε_Nd(t)=+5.7±0.2,代表了蛇绿岩的形成时代。超镁铁质岩石由不同成因的橄榄质糜棱岩和中粗粒橄榄岩组成,橄榄质糜棱岩是地幔橄榄岩经历复杂变形并多次部分熔融的残余体,具LREE亏损特征,其中发育橄榄石高温位错构造和高温组构以及低温位错构造和低温组构。中粗粒橄榄岩具LREE略富集的分布特征,是地幔橄榄岩残余体再次部分熔融熔体分离结晶的产物。野外地质、地球化学、构造变形特征均表明超镁铁岩块是因洋壳俯冲而底辟侵位于上覆玄武岩中的地幔橄榄岩残余体。综合分析认为,松树沟蛇绿岩经历了古陆块裂解或洋脊扩张(1271-1440Ma)-洋壳形成(1030-1271Ma)-洋壳俯冲消减-橄榄岩块底辟侵位(983Ma)-蛇绿岩构造侵位及其后构造变形叠加改造的复杂演化过程。  相似文献   

雅鲁藏布江开合带蛇绿岩地层   总被引：11，自引：0，他引：11  

朱占祥  滕云 《地层学杂志》1996,20(4):299-304

对西藏地层清理发现，沿雅鲁藏布江构造带分布的蛇绿岩，为具有类同正常沉积和沉积火山岩一样的有层、有序、有沉积构造及时代新老关系的蛇绿岩地层，它是特提斯洋开裂形成期的产物，赋予地层学的涵义，命名为雅鲁藏布江蛇绿岩群，从下至上建立变质橄榄岩组、堆积杂岩组、辉绿岩床（墙）组、枕状熔岩组及放射虫硅质岩、浊积岩组。它们构成完整的五套结构地层组合，生成时代为侏罗纪－白垩纪。新近区调成果表明，沿雅鲁藏布江构造带尚有中三叠世－晚三叠世时期蛇绿岩地层存在的可能性。雅鲁藏布江侏罗纪－白垩纪地层区划，其北与冈底斯－念青唐古拉地层区的界线，应划在日喀则群北界；其南应是雅鲁藏布江蛇绿岩群以南为界，南界同时是板块碰撞闭合边界或构造区划边界。  相似文献   

西准噶尔蛇绿混杂岩中的白云石大理岩和石榴角闪岩：早古生代残余洋壳深俯冲的证据   总被引：17，自引：11，他引：6  

朱永峰  徐新  陈博  薛云兴 《岩石学报》2008,24(12):2767-2777

本文在描述达拉布特和克拉玛依蛇绿岩中四个典型剖面(达拉布特、萨尔托海、白碱滩和百口泉)的基础上,通过研究变白云石大理岩和石榴角闪岩的形成和演化过程,展示西准噶尔蛇绿混杂岩的复杂性。白碱滩白云石大理岩是尖晶石二辉橄榄岩变质反应的产物。变质反应导致单斜辉石转变为白云石+石英+磁铁矿,橄榄石和斜方辉石先转变为蛇纹石+磁铁矿,蛇纹石再转变为白云石+石英+磁铁矿。透辉石+CO₂=白云石+石英+磁铁矿以及蛇纹石+CaCO₃=白云石+石英 +磁铁矿+H₂O这两个变质反应基本同时发生,他们以及石英—柯石英相变关系所限定的P-T空间(660~670℃,26.5~27.5 kbar)代表白云石大理岩的形成温度和压力。白云石大理岩与尖晶石二辉橄榄岩在一个不大的区域共存,说明循环到地球深部的尖晶石二辉橄榄岩(即：白云石大理岩的原岩)折返到地壳浅部后又与蛇绿岩中未俯冲的尖晶石二辉橄榄岩混杂在一起。因此,克拉玛依蛇绿混杂岩代表古俯冲带的位置。变辉长岩和尖晶石二辉橄榄岩中的单斜辉石均发育出溶结构(出溶尖晶石和斜方辉石)。这些出溶结构是蛇绿岩快速上升就位时由于温度和压力突然降低辉石发生分解反应的产物。因此,西准噶尔蛇绿混杂岩中的岩石组合记录着蛇绿岩形成时期、以及之后部分岩块通过俯冲带循环到地幔深处(最大深度~70km)并折返到地壳浅部的全过程。西准噶尔蛇绿混杂岩带是一个多时期、多阶段和多成因岩石的混杂体。  相似文献   

Geology and geochemistry of the Shuanggou ophiolite (Ailao Shan ophiolitic belt), Yunnan Province, SW China: Evidence for a slow-spreading oceanic basin origin   总被引：5，自引：0，他引：5  

Graciano P. Yumul Jr.  Mei-Fu Zhou  Christina Yan Wang  Tai-Ping Zhao  Carla B. Dimalanta 《Journal of Asian Earth Sciences》2008,32(5-6):385

The early Carboniferous Shuanggou ophiolite lies in the middle segment of the Ailao Shan orogenic belt between the South China Block to the north and the Indochina Block to the south. The ophiolite consists of meta-peridotite, gabbro, diabase and basalt, capped by radiolarian-bearing siliceous rocks. No layered gabbros or sheeted dikes have been observed. The meta-peridotite underwent low degrees of partial melting, consistent with the low magma budget of this oceanic lithosphere. Whole-rock rare earth element analyses of gabbro indicate a geochemical affinity with normal mid-ocean ridge basalts, consistent with the crystallization order of plagioclase followed by clinopyroxene recognized in the gabbros. The ophiolite is believed to have formed in a small, slow-spreading oceanic basin. Collision of the Indochina Block with the South China Block in the late Paleozoic was responsible for the closure of the oceanic basin and emplacement of the ophiolite in the Ailao Shan orogenic belt.  相似文献   

Geochronology and geochemistry of the Hegenshan ophiolitic complex: Implications for late-stage tectonic evolution of the Inner Mongolia-Daxinganling Orogenic Belt, China   总被引：47，自引：0，他引：47  

Laicheng Miao  Weiming Fan  Dunyi Liu  Fuqin Zhang  Yuruo Shi  Feng Guo 《Journal of Asian Earth Sciences》2008,32(5-6):348

The Hegenshan ophiolite in the Inner Mongolian-Daxinganling Orogenic Belt (IMDOB), northern China, consists of several discontinuous blocks composed dominantly of serpentinized ultramafic rocks with subordinate cumulate gabbros, mafic lavas and dikes, intruded by younger granodiorite dikes. The ultramafic rocks are highly depleted, serpentinized harzburgites with minor dunite, characterized by relative enrichment in large ion lithophile elements (LILE, e.g., Ba and Rb) and light rare earth elements (LREE). They are interpreted to be oceanic mantle that has undergone extensive melt extraction and variable degrees of metasomatism. The cumulate rocks consist mainly of gabbro and troctolite with LREE-depleted chondrite-normalized REE patterns showing significant positive Eu anomalies. They are enriched in LILE, depleted in Nb, and have high positive ε_Nd(t) (+8 to +11), suggesting derivation from a subduction-modified N-MORB-like source. The gabbros and mafic dikes have essentially the same age (295 ± 15 and 298 ± 9 Ma, respectively). The mafic dikes have flat to LREE-depleted, chondrite-normalized REE patterns, are depleted in Nb, enriched in LILE and have N-MORB-type Nd isotopic signatures (ε_Nd(t) = +8.1 to +10). The mafic lavas, erupted at 293 ± 1 Ma, can be divided into two groups; one composed of strongly deformed metabasalts similar in chemical and Nd–Sr isotopic compositions to the mafic dikes, and the other composed of undeformed and unmetamorphosed basalts with oceanic island basalt (OIB)-like trace element signatures and Nd isotopic compositions. The granodiorite dikes, which were intruded at 244 ± 4 Ma, have LREE-enriched, chondrite-normalized REE patterns with no Eu anomalies. Their abnormally high ε_Nd(t) values (+6.3 to +6.8) and low I_Sr (0.70412 to 0.70450) suggest formation from melts derived from thickened oceanic crust during or shortly after closure of the Paleo-Asian Ocean. The structure, lithology and geochemistry of the Hegenshan ophiolite suggest that it is a Cordilleran-type body formed in a supra-subduction zone (SSZ) environment and amalgamated by collision of several fragments of Paleo-Asian lithosphere. Final emplacement and amalgamation occurred in the latest Permian or earliest Triassic.  相似文献   

Southern borderland of Triassic Laurasia in north-east Iran     

A. W. Ruttner 《International Journal of Earth Sciences》1993,82(1):110-120

Results obtained by Iranian and European geoscientists in the critical area to the north-east of the North Iran Suture east of Mashhad are desribed and discussed. A slightly metamorphosed ophiolite belt, outcropping as the south easterly continuation of the previously known ophiolites of Mashhad along the north eastern perimeter of the Fariman-Torbat-e-Jam depression, proved to be either the remnant of a Permian ocean floor or more likely the remnant of a narrow ocean trough. There is as yet no proof of a Triassic age for this ophiolitic belt. To the north of this ophiolitic belt an epicontinental Triassic sequence is exposed at the southern edge of Laurasia in the erosional Window of Aghdarband. This is the result of intermittent sedimentation in a pull-apart basin along sinistral strike-slip faults. The Triassic of Aghdarband has much in common with other deposits of the Triassic Tethys; however, it shows a few unique features, e.g. the Early AnisianNicomedites fauna of a palaeobiogeographic North Tethyan Subprovince, or volcanogenic sedimentation during the late Anisian and the entire Ladinian.Permian ophiolites outcropping at the south-west corner of the Aghdarband erosional Window are transgressively overlain by basal conglomerats of this Triassic sequence. Hence the existence of a Triassic ocean south of Laurasia is very unlikely. This is an agreement with paleomagnetic data which suggest that the Central Iranian microcontinent was in direct contact with Laurasia during Triassic times. These palaeomagnetic data also suggest a clockwise rotation of the Central East Iran microplate during Triassic times (contrary to the anticlockwise rotation of this microplate in post-Triassic times). The sinistral strike-slip faulting and compression from the south-west which controls the structure of the Triassic may be derivative sequels to this clockwise rotation. All Eo-Cimmerian deformations of the Triassic rocks (e.g. folding, thrust faulting, strike-slip faulting) had stopped by Rhaetian times.  相似文献   

Geochemistry and petrogenesis of intrusive and extrusive ophiolitic plagiogranites, Central Anatolian Crystalline Complex, Turkey   总被引：15，自引：0，他引：15  

P. A. Floyd  M. K. Yaliniz  M. C. Goncuoglu 《Lithos》1998,42(3-4):225-241

Plagiogranites associated with the Sarikaraman ophiolite of the Central Anatolian Crystalline Complex, Turkey, closely resemble other plagiogranites from supra-subduction zone-type ophiolites of Neotethys. The ophiolite is remarkable in displaying a higher proportion of the plagiogranite suite (ca. 10% by volume) than is usually associated with such bodies. The Sarikaraman plagiogranites are represented by intrusive sheets and netvein trondhjemites largely developed at the top of the upper gabbros and as multiphase dykes within the sheeted dyke complex. The plagiogranite dykes are considered to feed extrusive silicified rhyolites associated with the basaltic lavas in the volcanic section of the ophiolite. Field relations suggest that the trondhjemites were probably generated from the roof section of a dynamic and evolving gabbroic magma chamber. Both the deep-seated trondhjemites and the volcanic rhyolites constitute the Sarikaraman plagiogranite suite. Geochemically there is complete overlap between the intrusive trondhjemites and extrusive rhyolites, which are characterised by (MORB-normalized) low HFS element contents with small negative Nb---Ta anomalies and variably enhanced LIL element abundances. Unlike other plagiogranites, however, the Sarikaraman suite is not characterized by consistently low K₂O contents; a feature that reflects the variable mobilization of the LIL elements under lower greenschist facies conditions. The REE are uniformly enriched relative to the basic components of the complex, but have similar normalized patterns exhibiting mild light REE depletion. In terms of their origin, the initial or most primitive plagiogranite melts could have been generated by either fractional crystallization (70–85% of clinopyroxene-feldspar ± amphibole) or partial melting (5–15% batch melting) of a gabbroic ‘source material’, although only the first process can produce most of the range of the plagiogranite compositions. As a group the plagiogranites exhibit some degree of internal variation which can be generated by further fractionation largely dominated by feldspar with minor apatite and amphibole.  相似文献   

西藏罗布莎铬铁矿体围岩方辉橄榄岩中的异常矿物   总被引：14，自引：8，他引：6  

杨经绥  张仲明  李天福  李兆丽  任玉峰  徐向珍  巴登珠  白文吉  方青松  陈松永  戎合 《岩石学报》2008,24(7)

近些年,我们在西藏罗布莎蛇绿岩型铬铁矿中发现金刚石和柯石英等超高压矿物和异常地幔矿物,成果多次在美国AGU会议上做特邀报告,发表在2007年(Geology)和国内期刊上,并有4个新矿物获得国际新矿物委员会批准.这些成果在国内外引起广泛关注,也引发出一系列新的科学问题,例如,金刚石的赋存状态,物质来源和成因?与其伴随的铬铁矿的成因,与金刚石的关系?两者形成的地质背景、物理化学环境、保存和运移的规律、机制,等等.为了探讨这些问题,我们认为除了研究罗布莎铬铁矿之外,还应该开展铬铁矿的围岩地幔橄榄岩的研究,看看它们中都有什么矿物,与铬铁矿中的矿物究竟存在什么异同以及两者之间的成因联系?为此,我们从西藏罗布莎铬铁矿31号矿体不同高度取回两个各自为1吨重的方辉橄榄岩围岩样品,开展人工重砂矿物的分选.通过矿物成分、激光拉曼和X射线衍射光谱的研究,从中识别出金刚石等50余种矿物.经初步对,认为铬铁矿围岩方辉橄榄岩中发现的矿物组合与铬铁矿中相似,表明两者存在成因上的联系,并可能共同经历了从深部到浅部的地质过程.  相似文献   

西藏丁青蛇绿岩中玻镁安山岩类侵入岩的地球化学特征   总被引：3，自引：0，他引：3  

张旗  杨瑞英 《岩石学报》1987,3(2)

丁青蛇绿岩中存在一套相当于玻镁安山岩(Boninite)系的侵入岩。其中的辉绿岩与MORB比较,以富Si、K、Rb和贫Ti、Zr、Y及HREE为特征,总REE丰度低,而LREE富集,类似于西太平洋马里亚纳岛弧中的玻镁安山岩。此外,辉长岩和斜长花岗岩亦以富大离子亲石元素和贫高场强元素为特征,而方辉橄榄岩则是十分难熔的。推测丁青蛇绿岩为岛弧类型的,产于洋内消减带之上的弧前环境,而不是在洋中脊上形成的。  相似文献