北喜马拉雅及藏南伸展构造综述

印度与欧亚大陆碰撞发生于65Ma左右,造山作用则开始于中新世初期,该造山运动形成南喜马拉雅的逆冲推覆体系,导致喜马拉雅山脉的隆起。然而,与造山作用的同时,北喜马拉雅及藏南地区却经历了广泛的伸展作用,所形成的伸展构造包括:①北喜马拉雅地区,开始于24Ma左右的藏南拆离系(STDS);②北喜马拉雅及藏南地区,开始于14Ma左右的南北向裂谷;③北喜马拉雅穹隆带,形成时间大致与南北向裂谷相同;④广布于青藏高原、开始于中新世末期、随机分布的高角度正断层。上述不同阶段的伸展构造形成于不同机制,并在喜马拉雅造山带的发展过程中起着不同的地质作用。其中,北喜马拉雅穹隆是一种特殊的伸展构造,并可能形成于多种机制。     

喜马拉雅造山带造山模式探讨

喜马拉雅是典型的碰撞型造山带,造山带结构构造复杂,可大致划分为以逆冲推覆构造为主的南喜马拉雅造山带和以各种伸展性构造为主的北喜马拉雅造山带,造山带内各类构造均发生过多期变形,且发生过多次缩短与伸展的构造反转,大喜马拉雅结晶杂岩系(GHC)内变形、岩浆及变质作用证明造山过程中存在渠道流作用。据此,本文提出一种由印度-欧亚大陆汇聚速率控制的多阶段造山模式:两大陆汇聚速度快时,青藏高原内形成南北向裂谷系(NSTR),喜马拉雅内经历造山过程,并在造山带中、下地壳形成作为底部拆离层的塑性层,汇聚速率慢时,青藏高原内形成共轭走滑断裂,喜马拉雅造山带内的塑性层发生松弛和重力扩散,形成渠道流,导致藏南拆离系(STDS)的启动、GHC的挤出和北喜马拉雅片麻岩穹窿(NHGD)的形成。上述的增厚与松弛均是在挤压体制下形成的,构造的反转是因挤压速率变化而产生的结构调节作用。     

喜马拉雅造山带亚东地区晚新生代剥露历史及其构造意义：来自磷灰石和锆石(U- Th)/He数据的约束

喜马拉雅造山带中部亚东地区位于藏南拆离系与南北向裂谷交汇处，是研究青藏高原南北向伸展和东西向伸展构造体制转换的关键地区，该地区新生代构造变形与冷却剥蚀过程对理解青藏高原的隆升历史和深部- 浅部动力学机制具有重要意义。本文对亚东地区开展两个剖面的磷灰石和锆石(U- Th)/He低温热年代学以及QTQt热史模拟分析，结果显示亚东地区大喜马拉雅结晶岩系剖面的10个磷灰石(U- Th)/He年龄分布范围为11.23~4.87 Ma，亚东- 谷露裂谷剖面的锆石和磷灰石(U- Th)/He年龄分别介于9.02~6.48 Ma和8.63~6.13 Ma。综合区域热年代学资料提出亚东地区大喜马拉雅结晶岩系自中新世以来经历了两期快速冷却事件：第一期为中新世中期(16~11 Ma)，由藏南拆离系（哲古拉拆离断层）伸展拆离作用控制的快速冷却，11 Ma前后冷却速率的明显转折变化指示了剥蚀驱动机制的转变，高原伸展体制开始向东西向伸展转换；第二期为中新世晚期到上新世(10~5 Ma)，期间存在由于亚东- 谷露裂谷伸展活动而导致的构造剥露，产生了9~6 Ma极快速冷却，平均冷却速率为290 ℃/Ma，约束了亚东- 谷露裂谷的启动时间为10 Ma左右。沿亚东藏南拆离系向南剖面上，磷灰石(U- Th)/He年龄数据总体呈现“老—新—老”的变化趋势，暗示了经历过部分熔融的大喜马拉雅结晶岩系通过中下地壳渠道流侧向挤出。综合已有的大喜马拉雅结晶岩系的结晶、冷却年代数据，提出大喜马拉雅结晶岩系的剥蚀冷却过程呈现多阶段和不等速特征，即存在25~11 Ma、10~5 Ma以及约3 Ma以来三个主要快速冷却阶段，受控于区域构造活动或者气候剧烈变化。     

喜马拉雅造山带东、西构造结的地质特征与对比

喜马拉雅造山带的东、西两端分别有一个构造急剧转向的地区——构造结, 这里是探讨喜马拉雅造山带构造演化的重要场所.区域地质调查资料对比显示这2个构造结有: (1)相似的地貌景观; (2)相似的地质特征和演化历史, 即都缺失喜马拉雅沉积岩(寒武纪—第三纪); (3)结晶岩系中都有高压变质岩, 且在10 Ma以来均发生过深熔与混合岩化作用; (4)25 Ma以来, 特别是10 Ma以来两地都经历了快速剥露和隆升作用; (5)印度板块-欧亚板块的碰撞时间接近, 分别为75 Ma和65 Ma, 均早于喜马拉雅造山带的其他地区.这些相似性表明: 伸展拆离和以河流作用为主的地表过程是喜马拉雅造山带的东、西构造结快速剥露的主导因素; 因强烈剥露减压所致的地壳部分熔融作用形成的岩浆向地表减压处的流动在构造结的演化过程中起着重要作用.      

高喜马拉雅的三维挤出模式

作为喜马拉雅造山带变质核的高喜马拉雅杂岩带,是以高级变质岩石、普遍的深熔反应以及高温韧性变形为主要特征的热碰撞造山带.在高喜马拉雅平行造山的韧性伸展构造发现的基础上,建立高喜马拉雅挤出的3-D构造模式,并提出了挤出的动力学过程:(1)造成高喜马拉雅中弱和热物质产生的局部熔融阶段(46～35 Ma),(2)平行造山的韧性伸展和重力裂陷阶段(28～26 Ma开始),(3)韧性逆冲型剪切带形成阶段(＞626～23 Ma),(4) MCT和STD的形成造成的高喜马拉雅挤出阶段(23～17 Ma).     

秦岭造山带中-新元古代(早期)地质演化

秦岭造山带是位于中国大陆中部并夹持于华北与扬子陆块之间的大陆造山带,是加里东期至印支期的碰撞造山带。对前加里东期演化虽然亦积累了不少资料,但认识上存在较大分歧。本文着重介绍秦岭造山带自中元古代晚期武关裂谷的打开(1243Ma±46Ma),中元古代末期松树沟洋盆的形成(1084Ma±73Ma～1030Ma±46Ma)以及新元古代早期同造山期花岗岩的侵入(960～840Ma)等自1.25Ga至0.84Ga期间的一系列热-构造事件,反映扬子大陆边缘前加里东期曾经历过一次“威尔逊构造旋回”,表明该区存在中—新元古代造山带的地质记录。但这次造山作用不是华北与扬子大陆的汇聚,而是曾属于扬子大陆边缘的“北秦岭变质地体”与其南的扬子大陆的一次汇聚过程。     

西藏拉琼锑金矿床流体包裹体特征及地质意义

正拉琼锑金矿床位于措美县西约17 km,大地构造位于青藏高原南部的特提斯喜马拉雅构造带东段,地处于印度河—雅鲁藏布江缝合带(IYZS)与藏南拆离系(STDS)大断裂之间。由于印度板块与欧亚板块碰撞之后,导致印度洋持续扩张,造成印度大陆不断向北挤压,形成喜马拉雅造山带(尹安,2000),该地区近东西向的断裂自北而南依次     

鄂尔多斯盆地西南部上古生界碎屑锆石U-Pb年龄及其构造意义

通过对鄂尔多斯盆地西南部晚古生代山西组1段和下石盒子组8段碎屑锆石进行LA-ICP-MS U-Pb测年分析,结合周缘地层年龄结构和地质历史事件,进而追寻盆地沉积物物源,推断盆地与造山带的盆山耦合过程。研究表明105个岩浆成因的碎屑锆石可分为4个年龄组段:(1)260~340 Ma,占总数的21.9%,推断物源主要来自北秦岭和西秦岭构造带;(2)370~470 Ma,占总数的24.8%,反映物源主要来自北秦岭、西秦岭构造带和北祁连造山带;(3)1600~2000 Ma,占总数的32.4%,指示物源来自北秦岭造山带、北祁造山带和华北板块;(4)2300~2600 Ma,占总数的15.2%,物源分别来自华北板块基底结晶岩系、北祁连构造带、北秦岭构造带和西秦岭构造带。研究区总体上具有来自北秦岭造山带、西秦岭造山带、北祁连造山带、兴蒙造山带及华北板块基底五个物源区,其中兴蒙造山带、北秦岭造山带和北祁连造山带为主要物源区。古生代碎屑锆石年龄证实了鄂尔多斯盆地西南部奥陶纪被动大陆边缘形成,志留纪—泥盆纪转化为陆-陆碰撞造山带,石炭纪—二叠纪逐渐由造山带转化为沉积盆地。     

北秦岭新元古代北北西向碰撞造山带存在的可能性及两侧陆块的汇聚与裂解

在北秦岭北西一北西西向显生宙造山带核部鉴别出与其斜交的北西向古构造带,可能为被改造了的北北西向新元古代造山带的残迹.强烈的区域变形(959～889Ma)和变质特别是高压变质(996～750Ma)以及S→I→A型花岗岩演化(959～725Ma)揭示,该造山带可能经历了同碰撞、晚碰撞到碰撞后伸展的碰撞造山旋回.由此推测,在该区新元古代时期可能发生了陆块的汇聚与裂解;当时造山带的原始方位及两侧汇聚陆块的边界可能是北北西向,汇聚方向可能是北东东向.     

根据碎屑白云母40Ar/39Ar年龄追索喜马拉雅造山带的剥落历史——对青藏高原隆升过程的启示

对喜马拉雅前陆盆地和孟加拉海扇中各地层的碎屑白云母40Ar/39Ar资料的系统分析揭示了喜马拉雅造山带自印度-欧亚板块碰撞开始造山以来的整个剥落历史: 剥落速率开始较为稳定,然后开始上升,在22Ma左右达到峰值,为4~5mm/a,随后急剧下降,最终以2mm/a的速率保持平稳。喜马拉雅造山带与青藏高原周缘剥落历史的对比约束了印度-欧亚板块碰撞造成青藏高原东缘和北缘的不同反应方式。即开始时的挤压主要被青藏高原北缘的大规模左旋走滑吸收, 到30Ma左右,喜马拉雅造山带冷却、剥落速率显著增强,北缘左旋走滑造成的柴达木地块的向东运动被华北板块阻挡而停滞,因此在北缘发生了一些重要的冷却和抬升剥落事件。至18Ma左右,喜马拉雅造山带的冷却、剥落速率继续增高并维持在较高水平,而该时间段内无论是北缘还是东缘,均未发生显著的抬升剥落事件,因此青藏高原的整体隆升和地壳增厚可能发生在此期间。中新世末—上新世初开始至今,青藏高原东缘龙门山地区发生了一些显著的抬升剥落事件,导致了大量的山崩和河流侵蚀,即此时来自喜马拉雅的挤压主要被青藏高原向东方向的地壳逃逸所吸收。     

Geologic and tectonic evolution of the Himalaya before and after the India-Asia collision

The geology and tectonics of the Himalaya has been reviewed in the light of new data and recent studies by the author. The data suggest that the Lesser Himalayan Gneissic Basement (LHGB) represents the northern extension of the Bundelkhand craton, Northern Indian shield and the large scale granite magmatism in the LHGB towards the end of the Palæoproterozoic Wangtu Orogeny, stabilized the early crust in this region between 2-1.9 Ga. The region witnessed rapid uplift and development of the Lesser Himalayan rift basin, wherein the cyclic sedimentation continued during the Palæoproterozoic and Mesoproterozoic. The Tethys basin with the Vaikrita rocks at its base is suggested to have developed as a younger rift basin (～ 900 Ma ago) to the north of the Lesser Himalayan basin, floored by the LHGB. The southward shifting of the Lesser Himalayan basin marked by the deposition of Jaunsar-Simla and Blaini-Krol-Tal cycles in a confined basin, the changes in the sedimentation pattern in the Tethys basin during late Precambrian-Cambrian, deformation and the large scale granite activity (～ 500 ± 50 Ma), suggests a strong possibility of late Precambrian-Cambrian Kinnar Kailas Orogeny in the Himalaya. From the records of the oceanic crust of the Neo-Tethys basin, subduction, arc growth and collision, well documented from the Indus-Tsangpo suture zone north of the Tethys basin, it is evident that the Himalayan region has been growing gradually since Proterozoic, with a northward shift of the depocentre induced by N-S directed alternating compression and extension. During the Himalayan collision scenario, the 10–12km thick unconsolidated sedimentary pile of the Tethys basin (TSS), trapped between the subducting continental crust of the Indian plate and the southward thrusting of the oceanic crust of the Neo-Tethys and the arc components of the Indus-Tangpo collision zone, got considerably thickened through large scale folding and intra-formational thrusting, and moved southward as the Kashmir Thrust Sheet along the Panjal Thrust. This brought about early phase (M1) Barrovian type metamorphism of underlying Vaikrita rocks. With the continued northward push of the Indian Plate, the Vaikrita rocks suffered maximum compression, deformation and remobilization, and exhumed rapidly as the Higher Himalayan Crystallines (HHC) during Oligo-Miocene, inducing gravity gliding of its Tethyan sedimentary cover. Further, it is the continental crust of the LHGB that is suggested to have underthrust the Himalaya and southern Tibet, its cover rocks stacked as thrust slices formed the Himalayan mountain and its decollement surface reflected as the Main Himalayan Thrust (MHT), in the INDEPTH profile.     

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

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。     

Active tectonics of Himalayan Frontal Fault system

In the Sub-Himalayan zone, the frontal Siwalik range abuts against the alluvial plain with an abrupt physiographic break along the Himalayan Frontal Thrust (HFT), defining the present-day tectonic boundary between the Indian plate and the Himalayan orogenic prism. The frontal Siwalik range is characterized by large active anticline structures, which were developed as fault propagation and fault-bend folds in the hanging wall of the HFT. Fault scarps showing surface ruptures and offsets observed in excavated trenches indicate that the HFT is active. South of the HFT, the piedmont zone shows incipient growth of structures, drainage modification, and 2–3 geomorphic depositional surfaces. In the hinterland between the HFT and the MBT, reactivation and out-of-sequence faulting displace Late Quaternary–Holocene sediments. Geodetic measurements across the Himalaya indicate a ~100-km-wide zone, underlain by the Main Himalayan Thrust (MHT), between the HFT and the main microseismicity belt to north is locked. The bulk of shortening, 15–20 mm/year, is consumed aseismically at mid-crustal depth through ductile by creep. Assuming the wedge model, reactivation of the hinterland faults may represent deformation prior to wedge attaining critical taper. The earthquake surface ruptures, ≥240 km in length, interpreted on the Himalayan mountain front through paleoseismology imply reactivation of the HFT and may suggest foreland propagation of the thrust belt.     

Kinematics and dynamics of the Namche Barwa Syntaxis, eastern Himalaya: Constraints from deformation, fabrics and geochronology

Field observations, deformation and fabric analyses, and precise age data acquired by zircon SHRIMP, LA-ICP-MS U-Pb and ⁴⁰Ar-³⁹Ar dating methods have yielded new constraints on the kinematics and dynamics of the Namche Barwa Syntaxis (NBS) which is the eastern corner of the Himalaya. A two-stage model has been established to explain the formation and evolution of the NBS. The northward indentation of the Indian plate beneath the Lhasa terrane began at 55-40 Ma, and crustal materials at this corner were subducted to depths > 70 km where they experienced HP (UHP?) metamorphism. Since 40 Ma, large-scale, right-lateral strike-slip along the Sagaing fault has accommodated the rapid northward movement of the eastern Indian plate corner with respect to the Indochina block. This caused significant and progressive bending of the Indus-Yarlung suture zone (IYSZ) such that it became the Dongjiu-Milin left-lateral, strike-slip, shear zone (DMSZ) in the west and the Aniqiao-Motuo right-lateral, strike-slip, shear zone (AMSZ) in the east. Both zones underwent strong mylonitization. Meanwhile, the HP (UHP?) metamorphic rocks were rapidly exhumed, first into the deep crust at 22-18 Ma and then to the shallow crust to form an antiformal dome at 6-2 Ma. Our model provides new insight into the processes of post-collisional crustal thickening related to the formation of the Himalayan orogenic belt.     

The longest voyage: Tectonic,magmatic, and paleoclimatic evolution of the Indian plate during its northward flight from Gondwana to Asia

The tectonic evolution of the Indian plate, which started in Late Jurassic about 167 million years ago (~ 167 Ma) with the breakup of Gondwana, presents an exceptional and intricate case history against which a variety of plate tectonic events such as: continental breakup, sea-floor spreading, birth of new oceans, flood basalt volcanism, hotspot tracks, transform faults, subduction, obduction, continental collision, accretion, and mountain building can be investigated. Plate tectonic maps are presented here illustrating the repeated rifting of the Indian plate from surrounding Gondwana continents, its northward migration, and its collision first with the Kohistan–Ladakh Arc at the Indus Suture Zone, and then with Tibet at the Shyok–Tsangpo Suture. The associations between flood basalts and the recurrent separation of the Indian plate from Gondwana are assessed. The breakup of India from Gondwana and the opening of the Indian Ocean is thought to have been caused by plate tectonic forces (i.e., slab pull emanating from the subduction of the Tethyan ocean floor beneath Eurasia) which were localized along zones of weakness caused by mantle plumes (Bouvet, Marion, Kerguelen, and Reunion plumes). The sequential spreading of the Southwest Indian Ridge/Davie Ridge, Southeast Indian Ridge, Central Indian Ridge, Palitana Ridge, and Carlsberg Ridge in the Indian Ocean were responsible for the fragmentation of the Indian plate during the Late Jurassic and Cretaceous times. The Réunion and the Kerguelen plumes left two spectacular hotspot tracks on either side of the Indian plate. With the breakup of Gondwana, India remained isolated as an island continent, but reestablished its biotic links with Africa during the Late Cretaceous during its collision with the Kohistan–Ladakh Arc (~ 85 Ma) along the Indus Suture. Soon after the Deccan eruption, India drifted northward as an island continent by rapid motion carrying Gondwana biota, about 20 cm/year, between 67 Ma to 50 Ma; it slowed down dramatically to 5 cm/year during its collision with Asia in Early Eocene (~ 50 Ma). A northern corridor was established between India and Asia soon after the collision allowing faunal interchange. This is reflected by mixed Gondwana and Eurasian elements in the fossil record preserved in several continental Eocene formations of India. A revised India–Asia collision model suggests that the Indus Suture represents the obduction zone between India and the Kohistan–Ladakh Arc, whereas the Shyok-Suture represents the collision between the Kohistan–Ladakh arc and Tibet. Eventually, the Indus–Tsangpo Zone became the locus of the final India–Asia collision, which probably began in Early Eocene (~ 50 Ma) with the closure of Neotethys Ocean. The post-collisional tectonics for the last 50 million years is best expressed in the evolution of the Himalaya–Tibetan orogen. The great thickness of crust beneath Tibet and Himalaya and a series of north vergent thrust zones in the Himalaya and the south-vergent subduction zones in Tibetan Plateau suggest the progressive convergence between India and Asia of about 2500 km since the time of collision. In the early Eohimalayan phase (~ 50 to 25 Ma) of Himalayan orogeny (Middle Eocene–Late Oligocene), thick sediments on the leading edge of the Indian plate were squeezed, folded, and faulted to form the Tethyan Himalaya. With continuing convergence of India, the architecture of the Himalayan–Tibetan orogen is dominated by deformational structures developed in the Neogene Period during the Neohimalayan phase (~ 21 Ma to present), creating a series of north-vergent thrust belt systems such as the Main Central Thrust, the Main Boundary Thrust, and the Main Frontal Thrust to accommodate crustal shortening. Neogene molassic sediment shed from the rise of the Himalaya was deposited in a nearly continuous foreland trough in the Siwalik Group containing rich vertebrate assemblages. Tomographic imaging of the India–Asia orogen reveals that Indian lithospheric slab has been subducted subhorizontally beneath the entire Tibetan Plateau that has played a key role in the uplift of the Tibetan Plateau. The low-viscosity channel flow in response to topographic loading of Tibet provides a mechanism to explain the Himalayan–Tibetan orogen. From the start of its voyage in Southern Hemisphere, to its final impact with the Asia, the Indian plate has experienced changes in climatic conditions both short-term and long-term. We present a series of paleoclimatic maps illustrating the temperature and precipitation conditions based on estimates of Fast Ocean Atmospheric Model (FOAM), a coupled global climate model. The uplift of the Himalaya–Tibetan Plateau above the snow line created two most important global climate phenomena—the birth of the Asian monsoon and the onset of Pleistocene glaciation. As the mountains rose, and the monsoon rains intensified, increasing erosional sediments from the Himalaya were carried down by the Ganga River in the east and the Indus River in the west, and were deposited in two great deep-sea fans, the Bengal and the Indus. Vertebrate fossils provide additional resolution for the timing of three crucial tectonic events: India–KL Arc collision during the Late Cretaceous, India–Asia collision during the Early Eocene, and the rise of the Himalaya during the Early Miocene.     

An overview of the metamorphic evolution in Central Nepal

This paper summarizes the studies of the metamorphic evolution of Central Nepal carried out by Nepali and international teams in the last 25 years. In Central Nepal, three metamorphic units are recognized. (1) The southernmost zone is the Lesser Himalaya, which is characterised by an inverted mineral zoning towards the Main Central Thrust (MCT) zone; (2) the Kathmandu nappe corresponds to an early (<22 Ma) out-of-sequence thrusting zone over the Lesser Himalaya along the Mahabharat thrust (MT) and is characterised by a Barrovian metamorphic evolution; (3) the Higher Himalayan Crystalline unit (HHC) is bounded at its base by the MCT and at its top by the South Tibetan Detachment system (STDS). It is characterised by successive tectonometamorphic episodes during the period spanning from 35–36 Ma to 2–3 Ma. Recent investigations suggest that the apparent metamorphic inversion througout the MCT zone does not reflect geothermal inversion. Instead, these investigations suggest successive cooling of the HHC along the MCT and the local preservation, above the MCT, of high-grade metamorphic rocks. The overall metamorphic history in Central Nepal from Oligocene to Pliocene, reflects the thermal reequilibration of rocks after thickening by conductive and advective heating and partial melting of the middle crust.     

中国西北部南北向伸展构造存在的新证据——酒泉早白垩世半地堑断陷成因初探

酒泉早白垩世半地堑断陷呈南北向或北东向展布，进一步分为多米诺骨牌式、对倾式和背倾式三种。其充填物明显地受近南北向或北东向正断裂控制，其中的火山岩均为碱性玄武岩，可能由地幔熔融形成。初步认为，酒泉半地堑断陷是早白垩世陆内地幔热隆诱发的近南北向伸展构造。在新生代，由于印度板块的挤压作用，北祁连山前展式北向推覆作用可能使早白垩世半地堑断陷的南部地区转换成山脉，现今的半地堑南部边界被掩伏于北祁连山之下；同时，印度板块的挤压作用使控制半地堑沉积体系的近南北向或北东向正断裂转换为逆冲断裂．发生反转。     

西南三江构造体系及演化、成因

西南三江构造体系突出表现为以昌都-兰坪-思茅地块为中轴的不对称走滑对冲构造,次为与走滑断裂相伴的伸展滑脱、走滑拉分盆地构造体系,再次为块体内部的近北东、北西向走滑断裂系。西南三江造山带构造体系演化分为挤压收缩变形、走滑深熔热隆、走滑剪切伸展、走滑剥蚀隆升等4个阶段。自晚白垩世开始,印度板块与欧亚板块碰撞,西南三江造山带对冲体构造体系初始形成。自渐新世开始,印度板块持续向北楔入欧亚大陆,印度板块与扬子克拉通构成力偶,两者相向、相对运动,挤压与剪切特提斯大洋缝合带及两大陆边缘弧盆系等地质体,西南三江造山带对冲体构造体系进一步发展,近南北向剪切走滑构造体系形成,构造方向也由近东西转为近南北向。而与近南北向主走滑断裂带之相伴的伸展滑脱构造、拉分盆地,块体内部近北东、北西“X”型剪切走滑断裂同时相伴形成。这样,就形成了西南三江造山带大规模的对冲、走滑、旋转及其伴生的伸展、拉分盆地构造的构造体系。     

喜马拉雅西部雅鲁藏布江缝合带地壳尺度的构造叠置

陆陆碰撞过程是板块构造缺失的链条。印度板块与亚洲板块的碰撞造就了喜马拉雅造山带和青藏高原的主体。然而,人们对印度板块在大陆碰撞过程中的行为尚不了解。如大陆碰撞及其碰撞后的大陆俯冲是如何进行的、印度板块是俯冲在青藏高原之下还是回转至板块上部(喜马拉雅造山带内)以及两者比例如何,这些仍是亟待解决的问题。印度板块低角度沿喜马拉雅主逆冲断裂(MHT)俯冲在低喜马拉雅和高喜马拉雅之下已经被反射地震图像很好地揭示。然而,关于MHT如何向北延伸,前人的研究仅获得了分辨率较低的接收函数图像。因而,MHT和雅鲁藏布江缝合带之间印度板块的俯冲行为仍是一个谜。喜马拉雅造山楔增生机制,也就是印度地壳前缘的变形机制,反映出物质被临界锥形逆冲断层作用转移到板块上部,或是以韧性管道流的样式向南溢出。在本次研究中,我们给出在喜马拉雅造山带西部地区横过雅鲁藏布江缝合带的沿东经81.5°展布的高分辨率深地震反射剖面,精细揭示了地壳尺度结构构造。剖面显示,MHT以大约20°的倾斜角度延伸至大约60 km深度,接近埋深为70~75 km的Moho面。越过雅鲁藏布江缝合带运移到北面的印度地壳厚度已经不足15 km。深地震反射剖面还显示中地壳逆冲构造反射发育。我们认为,伴随着印度板块俯冲,地壳尺度的多重构造叠置作用使物质自MHT下部的板块向其上部板块转移,这一过程使印度地壳厚度减薄了,同时加厚了喜马拉雅地壳。     

The “infiltrational-tension” dispersions halos

This paper reviews and integrates new results on: (1) the Late Paleozoic and Mesozoic evolution of Central Asia; (2) Cenozoic mountain building and intramontane basin formation in the Altay-Sayan area; (3) comparison of the tectonic evolutionary paths of the Altay, Baikal, and Tien Shan regions; (4) Cenozoic tectonics and mantle-plume magmatic activity; and (5) the geodynamics and tectonic evolution of Central Asia as a function of the India-Himalaya collision. It provides a new and more complete scenario for the formation of the Central Asian intracontinental mountain belt, compared with the generally accepted model of the “indentation” of the Indian plate into the Eurasian plate. The new model is based on the hypothesis of a complex interaction of lithospheric plates and mantle-plume magmatism. Compilation and comparison of new and published structural, geomorphological, paleomagnetic, isotopic, fission-track, and plume magmatism data from the Baikal area, the Altay, Mongolia, Tien Shan, Pamir, and Tibet show that the main stages of their orogenic evolution and basin sedimentation are closely related in time and space. After a long period of tectonic quiescence and peneplanation, Central and Southeast Asia were strongly affected by India-Eurasia collisional tectonics. During the first collisional stage (60 to 35 Ma), a first series of high mountains formed in the Himalayas, southern Tibet, and, possibly, the southern Tien Shan. Eocene deposits, younging northward, formed coevally with the orogeny in the near-Himalaya trough, Tarim, Tajik depression, and Fergana Basin. During postcollisional convergence, new depressions formed over wide territories, from the Tarim to Baikal and Altay areas. However, intensification of the deformation and uplift later were propagated northward, with development of the Qinghai-Tibetan Plateau (20 to 12 Ma), Tien Shan mountains (18 to 11 Ma), Junggar mountains and depression (8 to 5 Ma), and Altay, Baikal, and Transbaikal depressions and mountains (3 Ma).

Northward propagation of the deformation front from the Himalayan collision zone is suggested by regular northward younging of mountains and intramontane basins. Evidence of this includes: (1) India thrusting under Tibet, resulting in the rotation of the latter (60 to 35 Ma); (2) subsidence of the Tarim ramp depression, the rise of the Tien Shan, and the migration of both the Tien Shan and Tarim to the northwest along the Junggar and Talas-Fergana strike-slip faults (35 to 8 Ma); (3) subsidence of the Junggar plate, counterclockwise rotation of the Mongolian and Amur plates (8 to 3 Ma); and (4) rise of the Altay, Hangai, and Transbaikal areas, clockwise rotation of the Amur plate, and rapid opening of the Baikal rift. There is a clear relation between tectonics (rotation of the Tibet and Amur microplates, displacement along plate boundaries) and plume magmatism. The effects of the latter on moving plates are deduced from migration of the Tien Shan volcanic area toward the Tibet area and of the South Mongolian volcanic migration toward the Hangai area. Magmatism and tectonic processes became synchronous just after India collided with the South Himalaya area (60 Ma) and the Pamirs (35 Ma). Plumes beneath the Asian plate are considered to be responsible for the rotation of the microplates and for the northward propagation of tectonic activity from the zone of collision. Mantle magmatism is lacking beneath the Altay. In this case, mountain-building processes and basin-formation mechanisms likely are related to external sources of deformation originating from the India-Pamir convergence. In addition, they also may be related to the general translation and rotation of microplates.