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1.
利用古地磁数据，结合与构造活动有关的沉积记录以及古生物地理信息，对华南、思茅、保山、缅泰、印支、拉萨和喜马拉雅地块进行了古纬度和纬度运移量的对比研究，以确定云南西部三江地区主要地块的碰撞拼合历史。结果表明：(1)思茅地块可能源于华南地块；(2)保山和缅泰地块在晚石炭世至晚二叠世发生快速北移；(3)保山与华南地块于晚二叠世碰撞之后，和缅泰地块、华南地块以及印支地块继续向北漂移，直到晚三叠世；(4)保山与华南地块间的古特提斯洋可能于早志留世张开，晚二叠世闭合。 相似文献
2.
印度陆块新生代两次仰冲事件及其构造驱动机制:论印度洋、特提斯和欧亚板块相互作用 总被引：2，自引：2，他引：0
印度陆块与欧亚大陆的碰撞是印度洋扩张和特提斯洋闭合综合作用的结果。本文通过综合分析和研究提出这3个板块的相互作用致使印度陆块发生过2次向北的仰冲:早期(古新世末-始新世初,~57Ma)仰冲受其超高速运动(140mm/yr)的驱动,与特提斯之间产生的速度差致使两者间的边界发生破裂,密度小的印度陆块沿印度洋东经90°海岭和马尔代夫岛链向北仰冲到特提斯洋壳之上,两者的叠加导致印度陆块北缘——特提斯喜马拉雅地壳增厚(~70km)并且沉积了一套造山磨拉石——柳曲砾岩;晚期(渐新世-中新世之交,~25Ma)仰冲发生在碰撞后,由于高喜马拉雅结晶岩系沿主中央冲断带和藏南拆离断裂发生的垂向挤出,位于上盘的特提斯喜马拉雅沉积盖层同时发生重力垮塌,沿大喜马拉雅反冲断裂仰冲到冈底斯岩浆岩带之上并且造成后者的隆升和前陆下陷,其北缘充填了一套造山磨拉石沉积——大竹卡砾岩。这两次构造事件均受印度陆块的快速运动驱动。此外,在印度陆块超高速运动的挤压下,特提斯洋可能在早白垩世之后就停止了扩张,而老的洋壳不是俯冲消减了就是被仰冲的印度陆块掩盖了,这解释了为什么雅鲁藏布江缝合带只存早白垩世蛇绿岩。印度洋内东经90°海岭和马尔代夫岛链构成印度陆块的南东和南西边界,前者呈右行走滑,后者呈左行走滑,两者勾画出印度陆块向北漂移的轨迹。 相似文献
3.
杨宗让 《沉积与特提斯地质》2002,22(3):53-59
地处柴南缘昆中蛇绿杂岩带与羌塘地块北缘可可西里—金沙江古缝合线之间的松潘—甘孜褶皱带(包括东昆仑构造带)，其主体应属古特提斯洋晚石炭世一晚三叠世时期向其北侧的柴达木古陆南缘俯冲过程中在活动陆缘弧—沟间隙之间增生形成的一个大型弧前构造带。具有由弧前盆地沉积楔和基底增生杂岩构成的双重结构特点，其形成与冈瓦纳大陆北缘若尔盖“三角”地块的楔入及俯冲带向南迁移有关。大致经历了晚石炭世一早三叠世狭窄弧前盆地和中晚三叠世宽阔弧前盆地两个主要演化阶段。 相似文献
4.
通过1∶5万区域地质调查和收集相关资料的综合研究,本文对雅鲁藏布江结合带的形成演化作了进一步的探讨。雅鲁藏布江特提斯洋具有弧后扩张洋盆的性质,在早三叠世至中三叠世中期洋盆初步形成,中三叠世晚期至晚三叠世洋盆全面形成,从早侏罗世至晚白垩世洋盆逐步萎缩,到古新世至始新世关闭。南带的蛇绿岩主要为洋中脊扩张型(MORB型),形成于中三叠世晚期至晚三叠世。北带的蛇绿岩主要为与洋内俯冲相关的俯冲带上盘型(SSZ型),形成于早中侏罗世。带内侏罗纪至白垩纪其他岩浆岩主要为前弧玄武岩类(FAB型)。显示雅鲁藏布江特提斯洋从早侏罗世开始发生了洋内俯冲,并同步向北向冈底斯带之下主动俯冲消减和向南向喜马拉雅地块之下被动俯冲消减,持续发展到晚白垩世,在古新世至始新世俯冲碰撞消亡转化为结合带。 相似文献
5.
Vinod C. Tewari 《地学前缘》2000,(Z1)
RECENT ADVANCES IN GEOLOGICAL RESEARCH IN PARTS OF LESSER AND TETHYS HIMALAYA OF INDIA, SOUTH OF TIBETAN PLATEAU (KUMAON, GARHWAL AND ARUNACHAL PRADESH) 相似文献
6.
During the Triassic, the Thakkhola region of the Nepal Himalaya was part of the broad continental shelf of Gondwana facing a wide Eastern Tethys ocean. This margin was continuous from Arabia to Northwest Australia and spanned tropical and temperate latitudes.A compilation of Permian, Triassic and early Jurassic paleomagnetic data from the reconstructed Gondwana blocks indicates that the margin was progressively shifting northward into more tropical latitudes. The Thakkhola region was approximately 55° S during Late Permian, 40° S during Early Triassic, 30° S during Middle Triassic and 25° S during Late Triassic. This paleolatitude change produced a general increase in the relative importance of carbonate deposition through the Triassic on the Himalaya and Australian margins. Regional tectonics were important in governing local subsidence rates and influx of terrigenous clastics to these Gondwana margins; but eustatic sea-level changes provide a regional and global correlation of major marine transgressions, prograding margin deposits and shallowing-upward successions. A general mega-cycle characterizes the Triassic beginning with a major transgression at the base of the Triassic, followed by a general shallowing-upward of facies during Middle and Late Triassic, and climaxing with a regression in the latest Triassic. 相似文献
7.
重新认识中国斑岩铜矿的成矿地质条件 总被引：40，自引：10，他引：40
根据中国大陆洋陆作用的关系和造山带的演化，重新划分了中国斑岩铜矿成矿域和成矿带，将其分为古亚洲、北部特提斯、南部特提斯(喜马拉雅)和环太平洋4个成矿域。古亚洲成矿域又分为华北陆块北缘早-中古生代成矿带、哈萨克斯坦地块东北缘晚古生代成矿带、哈萨克斯坦地块南缘中晚古生代成矿带、西伯利亚板块西南缘晚古生代成矿带。特提斯北部成矿域分为中咱地块西缘晚三叠世义敦成矿带、羌塘地块(昌都-思茅地块)北缘古近纪玉龙成矿带、塔里木地块南缘晚古生代-新生代成矿带、扬子地块西缘古近纪成矿带。南部特提斯(喜马拉雅)成矿域分为班公错成矿带和冈底斯成矿带。环太平洋成矿域分晚中生代活动陆缘成矿带和台湾古近纪-新近纪岛弧成矿带。综合分析中国大陆地质演化史与斑岩铜矿成矿地质背景，对中国斑岩铜矿勘查工作具有重要参考价值。 相似文献
8.
中国南大陆为一构造古地理名称，在地理上包括昆仑、秦岭山脉以南的广大地区，泛称中国南方。这些地区在地质历史演化中分属于扬子陆块、华夏陆块、羌塘－昌都陆块、中咱微陆块，也包括由冈瓦纳陆块群裂解出来的拉萨陆块和印度陆块北缘的江孜地区。塔里木陆块和紫达木陆块在中国古大陆的聚合中裂解、漂称，在早古生代末脱离扬子陆块的群体，与华北陆块聚合，因此，中国南大陆古地理的重建，不仅涉及南方各块体的聚合，还涉及中国古大 相似文献
9.
新疆及周边古地磁研究与构造演化 总被引：20，自引：3，他引：17
新疆古地磁研究始于1979年,20年来通过对塔里木、准噶尔、昆仑山等地区的古地磁研究,获得了古生代—新生代塔里木板块、准噶尔板块和青藏板块古地磁极移曲线和古纬度资料。震旦纪以前塔里木板块尚未形成,晚震旦世在赤道附近各地块才联合成塔里木板块的主体部分。后经历了两次快速北移,一次快速南移。准噶尔板块早古生代为一个独立的微板块,在晚古生代与哈萨克斯坦板块联合成一体,组成了哈萨克斯坦-准噶尔板块;塔里木板块震旦纪时还属冈瓦纳大陆的一个组成部分,早古生代逐渐脱离了冈瓦纳大陆,快速向北漂移,晚古生代早期与准噶尔板块首次在东部碰撞,成为劳亚大陆南缘的一个增生体。将介于劳亚大陆和冈瓦纳大陆之间的古陆体,称之谓华夏古陆群。晚古生代末—中生代早期,华夏古陆群先后增生到劳亚大陆南缘;早古生代早期古特提斯洋尚未形成,诸地块处于冈瓦纳大陆范围内,位于南半球的赤道附近。在中-晚志留世,这些地(板)块才快速向北漂移,由于洋扩张,形成了古特提斯洋,构成了三大陆块群夹两个大洋的古地理格局;二叠纪是特提斯构造演化关键时期,晚侏罗-早白垩世昆仑地块与柴达木地块和塔里木地块发生碰撞,联合成一体。早侏罗世早期柴达木地块等与塔里木地块发生碰撞联合,造成了古特提斯洋消亡。早侏罗世中期,开 相似文献
10.
The timing of motion on major thrusts in the Western Himalaya shows an extremely complex sequence that spans approximately 70 Ma from the latest Cretaceous throughout the Tertiary. Three major phases of thrusting can be distinguished. The earliest phase (T1) is associated with emplacement of Tethyan basin thrust sheets (Lamayuru sediments and Spontang ophiolite) south and south-westwards onto the submerged northern passive margin of India (75-60 Ma). Collision between India and Asia occurred at 50-36 Ma and was followed immediately by the major phase (T2) of crustal shortening involving large-scale south and south-westward directed thrusting of the complete Palaeozoic, Mesozoic and Late Tertiary Tibetan—Tethys zone rocks. Preliminary balanced cross-sections show a minimum shortening of 126 km of these rocks across the Zanskar Range. The late collision phase (T3) involved re-thrusting of the previously stacked pile (breaching or leap-frog thrusting) reversing the earlier stacking order in places, and widespread steepening, overturning and backthrusting along the whole northern margin of the Tibetan—Tethys zone and throughout the Indus suture zone. 相似文献
11.
《Gondwana Research》2016,29(4):1530-1542
In this study, we conducted profile measurements, gravel composition analyses, and U–Pb dating on detrital zircons from a representative glacial marine diamictite in the Gangmaco–Dabure area of the Southern Qiangtang–Baoshan block, Tibetan Plateau. We conclude that the diamictite was formed in a glacial marine environment from the outer edge of the continental shelf to the continental slope and deep sea, in what is now the Southern Qiangtang–Baoshan block. Four distinct glacial–interglacial cycles were identified in the diamictite, which record a minimum of four stages of Gondwana glaciation in the area of the Southern Qiangtang–Baoshan block. Combined with regional geological information, we also conclude that during the Carboniferous–Permian, sediments containing the glacial marine diamictite derived from Gondwana, in the region extending from India to the Tethys Himalaya area, and Lhasa and Southern Qiangtang–Baoshan blocks, recorded the transition from continental, neritic to abyssal environments. Gravel assemblages and U–Pb dating of detrital zircons in the glacial marine diamictite indicate that the provenance of the diamictite was Indian Gondwana. We infer that during the Late Paleozoic, the northern margin of the Indian Gondwana continued to be influenced by the Early Palaeozoic tectonic set-up, when Indian Gondwana was under an erosional regime, and the Tethys Himalaya area, and Lhasa and Southern Qiangtang–Baoshan blocks were deposited on a passive continental margin. 相似文献
12.
昌宁-孟连特提斯洋的构造演化及其原特提斯与古特提斯的转换方式一直是青藏高原及邻区基础地质研究中最热门的科学问题之一.根据新的地质调查资料、研究成果并结合分析数据,系统总结了三江造山系不同构造单元地质特征,讨论了昌宁-孟连特提斯洋早古生代-晚古生代的构造演化历史.通过对不同构造单元时空结构的剖析和对相关岩浆、沉积及变质作用记录的分析,认为昌宁-孟连结合带内共存原特提斯与古特提斯洋壳残余,临沧-勐海一带发育一条早古生代岩浆弧带,前人所划基底岩系"澜沧岩群"应为昌宁-孟连特提斯洋东向俯冲消减形成的早古生代构造增生杂岩,滇西地区榴辉岩带很可能代表了俯冲增生杂岩带发生了深俯冲,由于弧-陆碰撞而迅速折返就位,这一系列新资料及新认识表明昌宁-孟连结合带所代表的特提斯洋在早古生代至晚古生代很可能是一个连续演化的大洋.在此基础上,结合区域地质资料,构建了三江造山系特提斯洋演化的时空格架及演化历史,认为其经历了早古生代原特提斯大洋扩张、早古生代中晚期-晚古生代特提斯俯冲消减与岛弧带形成、晚二叠世末-早三叠世主碰撞汇聚、晚三叠世晚碰撞造山与盆山转换等阶段. 相似文献
13.
本文以板块构造理论为基础,根据全球各大陆陆块和微陆块的相对亲缘性、统一性和独立性,提出晚前寒武纪末一早古生代初泛大陆解体后,整个古生代期间,全球大陆可划分为三大陆块群,即冈瓦纳大陆群、劳亚大陆群,和泛华夏大陆群。论述了三大陆块群,特别是泛华夏大陆群的形成演化及其作为独立大陆群存在的统一性。指出泛华夏大陆群的独立性和统一性表现在:①早古生代末,扬子、华夏(包括黄海一东海一南海古陆)、中朝、柴达木、塔里木、昆仑一北羌塘一昌都一印支等陆块曾一度拼贴在一起,形成统一的大陆;②晚古生代中晚期形成独立的华夏植物群区系;③晚古生代末一早中生代,泛华夏大陆群主体部分的扬子一华夏和中朝陆块向西运移楔入,导致其南北两侧古特提斯洋的同步消亡和全球泛大陆的最终形成。泛华夏大陆群的形成演化历经了晚前寒武纪末一早古生代初各陆块的裂离、割据;早古生代末的拼贴、统一;晚古生代的再次分裂和晚古生代末一早中生代与南北大陆群拼贴4个发展阶段。同时指出在东特提斯构造域内,古特提斯既表现出对原特提斯的继承性,又有新生性;中特提斯不是古特提斯的延续和发展,它是标志泛大陆裂一聚巨旋回演化中另一旋回的开始。最后讨论了显生宙地球上大陆由南聚北散到北聚南散,陆块在总体上向北漂移中旋转、裂、聚和泛大陆重组和立即又解体的可能的动力学机制,即地球内部物质向南半球运移,南半球膨胀,促使泛大陆解体。地球内部物质的南移又迫使软流层物质向北运动,驱动大陆碎块北上。蠕动的软流层中,除具有垂向环流的对流环外,还具有大小不等的水平涡旋运动。正是巨大的水平涡旋运动导致了陆块的旋转、会聚(泛大陆形成)和很快脱离涡旋体面离散(泛大陆解体)。 相似文献
14.
塔里木地块与古亚洲/特提斯构造体系的对接 总被引：32，自引：15，他引：17
塔里木盆地为环形山链所环绕,北缘为古亚洲体系的天山弧形山链,南缘为特提斯体系的西昆仑-阿尔金弧形山链。自新元古代晚期以来,塔里木地块及周缘地区经历了古亚洲洋盆和特提斯洋盆的开启、俯冲、闭合以及微陆块多次碰撞造山,发生多期的构造、岩浆及成矿作用。特别是受印度/亚洲碰撞(60~50Ma)以来的近程效应和远程效应影响,使塔里木盆地周缘发生强烈的隆升、缩短及走滑变形,形成了现今复杂的环型造山系,完成了古亚洲体系和特提斯体系与塔里木地块的最终对接。塔里木地块与周缘两大构造体系的焊接是从早古生代开始的。研究表明,早古生代末期塔里木已与西昆仑-阿尔金始特提斯造山系链接一起。此时,塔里木地块东段与中天山增生弧地体碰撞,而西段在晚古生代与中天山增生弧地体碰撞。塔里木盆地周缘早古生代造山系中存在早古生代中期和早古生代晚期的两次造山事件,致使塔里木盆地内映现两个早古生代构造不整合面:晚奥陶世-志留纪之间的角度不整合和中晚泥盆世与早古生代之间的角度不整合。塔里木盆地早古生代的古地理、古环境和古构造研究表明,塔里木早古生代台地位于盆地的中西部,盆地东部为陆缘斜坡和深海/半深海沉积盆地,与南天山早古生代被动陆缘链接。印度/亚洲碰撞导致塔里木盆地西南缘的喜马拉雅西构造结的形成与不断推进,使特提斯构造体系与古亚洲构造体系在西构造结处靠拢及对接,终使塔里木盆地最后定型。 相似文献
15.
晚古生代-中三叠世,中国南方在陆块间离散-聚合的不同构造运动体制下,分别在扬子陆块内部和边缘形成了不同的盆地原型及其演化序列.在扬子陆块的西南缘,主要形成裂谷-被动大陆边缘坳陷-弧后盆地的原型演化序列;扬子陆块南缘发育裂谷到台内坳陷再到裂谷原型演化序列;扬子陆块内部主要形成台内拗陷-裂谷的原型演化序列.古特提斯洋演化对晚古生代构造和盆地原型的演化起决定性作用. 相似文献
16.
The early Albian Oceanic Anoxic Event (OAE), i.e., OAE1b, is well documented in western Tethys and in the primary North Atlantic Ocean, but has not yet been reported from eastern Tethys. In this paper, we present bulk carbon isotope data of hemipelagites to examine if it was recorded in eastern Tethys. Samples were taken from the upper Chuangdepu Member (nannofossil zone CC8) of the lower Gyabula (former Shadui) Formation at the Bangbu section, Qonggyai, southern Tibet of China. The δ13C values mainly range from −0.6‰ to 1.8‰ with a maximum of 1.87‰ and a minimum of −0.69‰. Three stages of carbon isotope evolution were distinguished with three boundaries. By the constraint of the stratigraphic sequence and nannofossil biostratigraphic zone CC8, the rapid δ13C change and correlation with western Tethys and Atlantic Ocean together suggest that these three boundaries of the carbon isotope evolution probably correspond to three subevents of the early Albian OAE1b, and the subevent levels of upper Kilian, Paquier, and Leenhardt are recorded in eastern Tethys (southern Tibet). The fact that the amount of δ13C shift is less by ∼1.5–2.0‰ in eastern Tethys than in western Tethys and Atlantic Ocean is interpreted as a result of possible cool sea surface (∼14–16 °C) of the southeastern Tethys (northern Indian passive margin of Greater India), which was probably located in a medium–high latitude during the Albian, leading to low primary productivity. The recognition of OAE-1b from Tethys Himalaya can improve our understanding of the Tethys and global paleoclimatic and paleoceanographic changes during the mid-Cretaceous. 相似文献
17.
《Journal of Asian Earth Sciences》1999,17(5-6):805-827
The sedimentary history of the Nepal Tethys Himalaya began with deposition of thick carbonates in the Cambro?–Ordovician, followed by a mixed siliciclastic–carbonate epicontinental succession recording two major deepening events in the Early Silurian and Late Devonian. Fossiliferous carbonate ramp deposits in the Tournaisian were disconformably followed by white quartzose sandstones and black mudrocks with locally intercalated diamictites derived from sedimentary rocks and deposited in asymmetric tectonic basins (“rift stage”). Break-up in the mid-Early Permian, locally associated with effusion of tholeiitic lava flows, was followed by a transgressive sandy to shaly, locally coal-bearing or bioclastic unit capped by condensed pelagic carbonates in the Middle to Late Permian (“juvenile ocean stage”). Subsidence of the cooling stretched crust led close to bathyal water depths in the Olenekian, but then slowed down in the Middle Triassic to increase again sharply in the Late Triassic owing to renewed extensional tectonic activity and sediment loading during up- and out-building of the Indian continental terrace. Deposition of tropical platform carbonates finally became widespread in the middle Liassic (“mature passive margin stage”). The initial fragmentation of Gondwana in the Middle Jurassic led to rejuvenation of the Indian craton and deposition of quartzo-feldspathic hybrid arenites, capped by condensed oolitic ironstones deposited at warm subtropical latitudes in the late Bathonian/middle Callovian. Next, a discontinuous pelagic grey marly limestone unit was followed by the ammonoid-rich offshore Spiti Shale in the Late Jurassic. The final disintegration of Gondwana began in the Berriasian, when quartzose siliciclastics derived again from the rejuvenated Indian craton and partly from recycling of older clastic successions were followed by thick deltaic to shelf volcaniclastics documenting eruption of alkali basalts in the Valanginian? followed in the Hauterivian to Albian by more felsic differentiates such as the trachyandesites exposed in the Lesser Himalaya 120 km to the south. A widespread drowning episode, fostered by waning volcaniclastic supply during a global eustatic rise, is documented by a major glauconitic horizon deposited at middle southern latitudes in the late Albian, overlain by “Scaglia-like” pelagic limestones in the latest Albian. The final part of sedimentary history, during the rapid northward flight of India and its collision with Eurasia, is not documented anywhere in Nepal due to later erosion of Upper Cretaceous to Lower Tertiary strata. 相似文献
18.
造山带内动力作用的工程效应是地学与工程领域基础科学研究的前沿问题。结合GIS技术和相关地学理论,对喜马拉雅造山带由构造划分的高喜马拉雅、低喜马拉雅和特提斯喜马拉雅3个地块进行研究,揭示不同地块工程地质特性和灾害效应受内动力制约的普适性规律。提出:在挤压碰撞造山机制作用下快速隆升的高、低喜马拉雅,地震以逆冲型为主,地震强度大、频率高,水平应力相对较大,主应力方向近NE-WS方向,地形向大高差发展、河流下切强烈,山地灾害严重;而属于拆离地系,处于相对沉陷状态的特提斯喜马拉雅,地震以正断型为主,地震活动性相对较弱,水平应力相对较小,主应力方向近E-W方向,地形演化向着减弱地势的趋向发展,雪崩灾害严重;此外,高喜马拉雅特有的海洋性冰川地貌、冰湖和冰川泥石流,可能是控制跨喜马拉雅山铁路线路方案的重要问题。基于上述各地块工程效应存在显著差异的认识,提出以构造划分作为铁路工程地质分区的建议,并以拟建中尼铁路交通廊道为例,绘制了工程地质分区图。研究有助于将造山带理论推进到工程应用层面,为铁路大范围方案比选阶段,广域、高效、低成本地获取信息提供了新途径。 相似文献
19.
Yeşim İslamoğlu Mathias Harzhauser Martin Gross Gonzalo Jiménez-Moreno Stjepan Coric Andreas Kroh Fred Rögl Jan van der Made 《International Journal of Earth Sciences》2010,99(1):183-200
The Oligocene depositional history of the Thrace Basin documents a unique paleogeographic position at a junction between the
Western Tethys and the Eastern Paratethys. As part of the Tethys, shallow marine carbonate platforms prevailed during the
Eocene. Subsequently, a three-staged process of isolation started with the Oligocene. During the Early Rupelian, the Thrace
Basin was still part of the Western Tethys, indicated by typical Western Tethyan marine assemblages. The isolation from the
Tethys during the Early Oligocene is reflected by oolite formation and endemic Eastern Paratethyan faunas of the Solenovian
stage. The third phase reflects an increasing continentalisation of the Thrace Basin with widespread coastal swamps during
the Late Solenovian. The mollusc assemblages are predominated by mangrove dwelling taxa and the mangrove plant Avicennia is recorded in the pollen spectra. The final continentalisation is indicated by the replacement of the coastal swamps by
pure freshwater swamps and fluvial plains during the Late Oligocene (mammal zone MP 26). This paleogeographic affiliation
of the Thrace Basin with the Eastern Paratethys after ~32 Ma contrasts all currently used reconstructions which treat the
basin as embayment of the Eastern Mediterranean basin. 相似文献
20.
Tethyan and Indian subduction viewed from the Himalayan high- to ultrahigh-pressure metamorphic rocks 总被引：13，自引：0，他引：13
The Himalayan range is one of the best documented continent-collisional belts and provides a natural laboratory for studying subduction processes. High-pressure and ultrahigh-pressure rocks with origins in a variety of protoliths occur in various settings: accretionary wedge, oceanic subduction zone, subducted continental margin and continental collisional zone. Ages and locations of these high-pressure and ultrahigh-pressure rocks along the Himalayan belt allow us to evaluate the evolution of this major convergent zone.
(1) Cretaceous (80–100 Ma) blueschists and possibly amphibolites in the Indus Tsangpo Suture zone represent an accretionary wedge developed during the northward subduction of the Tethys Ocean beneath the Asian margin. Their exhumation occurred during the subduction of the Tethys prior to the collision between the Indian and Asian continents.
(2) Eclogitic rocks with unknown age are reported at one location in the Indus Tsangpo Suture zone, east of the Nanga Parbat syntaxis. They may represent subducted Tethyan oceanic lithosphere.
(3) Ultrahigh-pressure rocks on both sides of the western syntaxis (Kaghan and Tso Morari massifs) formed during the early stage of subduction/exhumation of the Indian northern margin at the time of the Paleocene–Eocene boundary.
(4) Granulitized eclogites in the Lesser Himalaya Sequence in southern Tibet formed during the Paleogene underthrusting of the Indian margin beneath southern Tibet, and were exhumed in the Miocene.
These metamorphic rocks provide important constraints on the geometry and evolution of the India–Asia convergent zone during the closure of the Tethys Ocean. The timing of the ultrahigh-pressure metamorphism in the Tso Morari massif indicates that the initial contact between the Indian and Asian continents likely occurred in the western syntaxis at 57 ± 1 Ma. West of the western syntaxis, the Higher Himalayan Crystallines were thinned. Rocks equivalent to the Lesser Himalayan Sequence are present north of the Main Central Thrust. Moreover, the pressure metamorphism in the Kaghan massif in the western part of the syntaxis took place later, 7 m.y. after the metamorphism in the eastern part, suggesting that the geometry of the initial contact between the Indian and Asian continents was not linear. The northern edge of the Indian continent in the western part was 300 to 350 km farther south than the area east of the Nanga Parbat syntaxis. Such “en baionnette” geometry is probably produced by north-trending transform faults that initially formed during the Late Paleozoic to Cretaceous Gondwana rifting. Farther east in the southern Tibet, the collision occurred before 50.6 ± 0.2 Ma. Finally, high-pressure to ultrahigh-pressure rocks in the western Himalaya formed and exhumed in steep subduction compared to what is now shown in tomographic images and seismologic data. 相似文献