Neoproterozoic Crustal Evolution of Northwestern Indian Shield: Implications on Break up and Assembly of Supercontinents

The Neoproterozoic geological history in western Rajasthan, northwest Indian Shield began with the intrusion of anorogenic bodies of diorites at ca. 1000 Ma. Recently available single zircon dates indicate possible continuity of the “Grenville belt” beyond Eastern Ghats through the Satpura Orogenic Belt into the Aravalli Mountains. Closely following this tectono-thermal event at the Meso-Neoproterozoic boundary, some narrow basins opened west of the Aravalli Mountains. The basin closing related to the tectonic inversion and associated magmatism at ca. 835 Ma completed the cratonisation process of the Precambrian Aravalli crust. Subsequent geological events witnessed over a wide region to the southwest of the Aravalli Mountains, were in the form of “plume-related” magmatism of the Malani Group, which comprises bimodal volcanics (dominantly felsic and minor mafic), minor sediments, and peraluminous and peralkaline granitoids. An unconformity indicating a hiatus is noticed at the base of the Malani Group. The final phase of the Neoproterozoic cratonic history is associated with thick platformal deposits of the Marwar Supergroup. The Marwar basins show a clear sedimentological affiliation with the sub-Himalayan basin of “Saline Series” in Pakistan.The beginning of the Neoproterozoic history in the northwestern Indian Shield is correlated with the events related to the possible break up of the Rodinia Supercontinent. Much of the later phases of the Neoproterozoic geological events witnessed in the Indian Shield are traditionally described as the “Pan-African”. However, the geological events recorded in the northwestern part of Indian Shield are neither strictly coeval nor are tectonically correlatable with the ‘orogeny and fabric-forming contemporary events’ of the East African Orogeny (EAO), which is undoubtedly the type terrane of the Pan-African Tectono-thermal Belt. The evolution of the northwestern Indian Shield during the Neoproterozoic does not appear to be related in any way with the Pan-African events observed in EAO. Further, the most talked about ‘Pan-African’ dates at ca. 500±50 Ma, are manifestations of anorogenic thermal event, which possibly marks an aborted attempt to fragment the ‘Greater Gondwana’ during the early Palaeozoic.     

An evolutionary model of the western churchill province and western margin of the superior province in Canada and the North-Central United States

Regional-scale geophysical information, which includes aeromagnetic, gravity, seismic refraction, multi-channel seismic reflection and electromagnetic induction data, is used to extend our knowledge of the Canadian Shield beneath the Phanerozoic Williston basin of south-central Canada and the north-central United States. A new tectonic map based on this information shows the Proterozoic Flin Flon-Snow Lake and La Ronge-Lynn Lake volcanic island arcs and their associated fore-arc (Kisseynew belt) and back-arc (Reindeer-South Indian Lakes belt) basins wedged between the Archean Superior craton on the east and the Archean parts of the Churchill and Wyoming cratons on the west. Along the western margin of the Superior craton the Thompson nickel belt, including its extension southwards beneath the Williston basin, is interpreted to have been successively the site of continental rifting and rupturing, an evolving continental margin, a continent-volcanic island arc “suture” zone and eventually a continental-scale strike-slip fault. The North American Central Plains electrical conductivity anomaly and closely related seismic low-velocity zones are explained by the presence in the lower crust of buried slices of hydrated oceanic-type material, situated within the southward extension of the Reindeer-South Indian Lakes remnant back-arc basin and adjoining tectonic units. A new plate tectonic model is proposed for this region that involves the rifting and rupturing of the Archean continents and the opening and closing of one or more oceanic basins. This model is shown to be consistent with most of the geological, geophysical and geochronological data that pertains to the Proterozoic evolution of the exposed Shield and similar geophysical data and subsurface geochronological information from further south.     

Regional tectonic framework,structure and evolution of the western marginal basins of India

The Kutch-Saurashtra, Cambay and Narmada basins are pericontinental rift basins in the western margin of the Indian craton. These basins were formed by rifting along Precambrian tectonic trends. Interplay of three major Precambrian tectonic trends of western India, Dharwar (NNW-SSE), Aravalli-Delhi (NE-SW) and Satpura (ENE-WSW), controlled the tectonic style of the basins. The geological history of the basins indicates that these basins were formed by sequential reactivation of primordial faults. The Kutch basin opened up first in the Early Jurassic (rifting was initiated in Late Triassic) along the Delhi trend followed by the Cambay basin in the Early Cretaceous along the Dharwar trend and the Narmada basin in Late Cretaceous time along the Satpura trend. The evolution of the basins took place in four stages. These stages are synchronous with the important events in the evolution of the Indian sub-continent—its breakup from Gondwanaland in the Late Triassic-Early Jurassic, its northward drifting during the Jurassic-Cretaceous and collision with the Asian continent in the Early Tertiary. The most important tectonic events occurred in Late Cretaceous time. The present style of the continental margins of India evolved during Early Tertiary time.The Saurashtra arch, the extension of the Aravalli Range across the western continental shelf, subsided along the eastern margin fault of the Cambay basin during the Early Cretaceous. It formed an extensive depositional platform continuous with the Kutch shelf, for the accumulation of thick deltaic sediments. A part of the Saurashtra arch was uplifted as a horst during the main tectonic phase in the Late Cretaceous.The present high thermal regime of the Cambay-Bombay High region is suggestive of a renewed rifting phase.     

Break Up of Australia-India-Madagascar Block, Opening of the Indian Ocean and Continental Accretion in Southeast Asia With Special Reference to the Characteristics of the Peri-Indian Collision Zones

Linear belts of Gondwana basins developed in the Indian continent since Late Palaeozoic along favoured sites of Precambrian weak zones like cratonic sutures and reactivated mobile belts. The Tibetan and Sibumasu - West Yunnan continental blocks, that were located adjacent to proto-Himalayan part of the Indian continent, rifted and drifted from the northern margin of the East Gondwanic Indo-Australian continent, during Late Palaeozoic, when the said northern margin was under glacial or cool climatic condition and rift-drift tectonic setting. The Indo-Burma-Andaman (IBA), Sikule, Lolotoi blocks were also rifted and drifted from the same northern margin during Late Jurassic. This was followed by the break-up of the Australia-India-Madagascar continental block during the Cretaceous. The activity was associated with hot spot related volcanism and opening up of the Indian Ocean. The Late Cretaceous and Tertiary phases of opening of the Arabian Sea succeeded the Early Cretaceous phase of opening of the Bay of Bengal, part of the Indian Ocean. The Palaeo- and Neo-Tethyan sutures in Tibet, Yunnan, Laos, Thailand and Vietnam reveal the complex opening and closing history of the Tethys. The IBA block rotated clockwise from its initial E-W orientation because of 90°E and adjacent dextral transcurrent fault movements caused due to faster northward movement of the Indian plate relative to that of Australia. The India-Tibet terminal collision during Early-Middle Eocene initiated Himalayan orogenesis and contemporaneously there was foreland basin development that was accompanied with sporadic but laterally extensive continental-flood-basalt (CFB) type and related volcanism. The Paleogene rocks of the Himalayan foreland basin are involved in tectonism and are mostly concealed under older rocks.

The Mesozoic-Early Eocene ophiolite terrane on IBA does not represent the eastern suture of the Indian plate but occurs as klippe on IBA, caused due to oblique collision between Sibumasu and IBA during Late Oligocene. Post-collisional indentation of Y-shaped Indian continent into the Asian collage produced Himalayan syntaxes, clockwise rotation of the Sibumasu block which was then sutured to the Tibetan and SE Asian blocks, and tectonic extrusion of the Indochina block along the Ailao Shan Red River (ASRR) shear zone. Highly potassic magmatic rocks were emplaced during Late Palaeogene at the oroclinally flexed marginal parts of the South China continental lithosphere. These magmatic bodies were dislocated by the ASRR left lateral shear zone soon afterwards. Petrogenetic and tectonic processes that generated the Eocene CFB volcanics at the Himalayan foreland basin may have also produced Late Palaeogene magmatism from outer parts of the Namche-Barwa Syntaxis. Their site-specific location and time sequence suggest them to be genetically related to the India-Asia collision process and Indian continent's indentation-induced syntaxial buckling. Deep mantle-reaching fractures were apparently produced during India-Asia terminal collision at the strongly flexed leading brittle edge of the Indian continental lithosphere, and possibly later in time at the outer oroclinally bent marginal parts of the rigid South China continental lithosphere, generating typical magma.

The subduction zone that developed along the western margin of IBA due to oblique convergence between the IBA and the Indian plate is still active. The northern end of IBA ultimately collided with the NE prolongation of the Indian continent and was accreted to it during Mio-Pliocene. The Shillong massif was uplifted and overthrust over the Bengal Basin located over its passive margin to the south, whereas, the Eocene distal shelf sediments of IBA were overthrust over the Tertiary shelf of the Indian continent.     

Palaeozoic and Mesozoic tectonic evolution and palaeogeography of East Asian crustal fragments: The Korean Peninsula in context

East and Southeast Asia comprises a complex assembly of allochthonous continental lithospheric crustal fragments (terranes) together with volcanic arcs, and other terranes of oceanic and accretionary complex origins located at the zone of convergence between the Eurasian, Indo-Australian and Pacific Plates. The former wide separation of Asian terranes is indicated by contrasting faunas and floras developed on adjacent terranes due to their prior geographic separation, different palaeoclimates, and biogeographic isolation. The boundaries between Asian terranes are marked by major geological discontinuities (suture zones) that represent former ocean basins that once separated them. In some cases, the ocean basins have been completely destroyed, and terrane boundaries are marked by major fault zones. In other cases, remnants of the ocean basins and of subduction/accretion complexes remain and provide valuable information on the tectonic history of the terranes, the oceans that once separated them, and timings of amalgamation and accretion. The various allochthonous crustal fragments of East Asia have been brought into close juxtaposition by geological convergent plate tectonic processes. The Gondwana-derived East Asia crustal fragments successively rifted and separated from the margin of eastern Gondwana as three elongate continental slivers in the Devonian, Early Permian and Late Triassic–Late Jurassic. As these three continental slivers separated from Gondwana, three successive ocean basins, the Palaeo-Tethys,. Meso-Tethys and Ceno-Tethys, opened between these and Gondwana. Asian terranes progressively sutured to one another during the Palaeozoic to Cenozoic. South China and Indochina probably amalgamated in the Early Carboniferous but alternative scenarios with collision in the Permo–Triassic have been suggested. The Tarim terrane accreted to Eurasia in the Early Permian. The Sibumasu and Qiangtang terranes collided and sutured with Simao/Indochina/East Malaya in the Early–Middle Triassic and the West Sumatra terrane was transported westwards to a position outboard of Sibumasu during this collisional process. The Permo–Triassic also saw the progressive collision between South and North China (with possible extension of this collision being recognised in the Korean Peninsula) culminating in the Late Triassic. North China did not finally weld to Asia until the Late Jurassic. The Lhasa and West Burma terranes accreted to Eurasia in the Late Jurassic–Early Cretaceous and proto East and Southeast Asia had formed. Palaeogeographic reconstructions illustrating the evolution and assembly of Asian crustal fragments during the Phanerozoic are presented.     

Thermo-mechanical structure of the southern part of the Indian Shield and its relevance to Precambrian basin evolution

The thermal and mechanical structures of the southern part of the Precambrian Indian Shield have been estimated using available heat flow data and shear stress profiles from olivine rheology. These and other geological, geochronological and geophysical data including deep seismic studies (DSS) profiles of Proterozoic Cuddapah basin on South Indian Shield, are utilized to examine thermal models for the evolution of Precambrian intracratonic, platform basins on the Archean lithosphere of Indian Shield. Evidence of mantle perturbations and cycles of thermal events are documented to be important in the Cuddapah basin's evolution. Haxby et al.'s (1976) thermal model has been shown to explain the Cuddapah basin's flexuring and magnitude of subsidence.     

Subduction,mega-shear systems and Late Palaeozoic basin development in the African segment of Gondwana

 Basins within the African sector of Gondwana contain a Late Palaeozoic to Early Mesozoic Gondwana sequence unconformably overlying Precambrian basement in the interior and mid-Palaeozoic strata along the palaeo-Pacific margin. Small sea-board Pacific basins form an exception in having a Carboniferous to Early Permian fill overlying Devonian metasediments and intrusives. The Late Palaeozoic geographic and tectonic changes in the region followed four well-defined consecutive events which can also be traced outside the study area. During the Late Devonian to Early Carboniferous period (up to 330 Ma) accretion of microplates along the Patagonian margin of Gondwana resulted in the evolution of the Pacific basins. Thermal uplift of the Gondwana crust and extensive erosion causing a break in the stratigraphic record characterised the period between 300 and 330 Ma. At the end of this period the Gondwana Ice Sheet was well established over the uplands. The period 260–300 Ma evidenced the release of the Gondwana heat and thermal subsidence caused widespread basin formation. Late Carboniferous transpressive strike-slip basins (e.g. Sierra Australes/Colorado, Karoo-Falklands, Ellsworth-Central Transantarctic Mountains) in which thick glacial deposits accumulated, formed inboard of the palaeo-Pacific margin. In the continental interior the formation of Zambesi-type rift and extensional strike-slip basins were controlled by large mega-shear systems, whereas rare intracratonic thermal subsidence basins formed locally. In the Late Permian the tectonic regime changed to compressional largely due to northwest-directed subduction along the palaeo-Pacific margin. The orogenic cycle between 240 and 260 Ma resulted in the formation of the Gondwana fold belt and overall north–south crustal shortening with strike-slip motions and regional uplift within the interior. The Gondwana fold belt developed along a probable weak crustal zone wedged in between the cratons and an overthickened marginal crustal belt subject to dextral transpressive motions. Associated with the orogenic cycle was the formation of mega-shear systems one of which (Falklands-East Africa-Tethys shear) split the supercontinent in the Permo-Triassic into a West and an East Gondwana. By a slight clockwise rotation of East Gondwana a supradetachment basin formed along the Tethyan margin and northward displacement of Madagascar, West Falkland and the Gondwana fold belt occurred relative to a southward motion of Africa. Received: 2 October 1995 / Accepted: 28 May 1996     

Features,provenance, and tectonic significance of Carboniferous–Permian glacial marine diamictites in the Southern Qiangtang–Baoshan block,Tibetan Plateau

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.     

The phanerozoic sedimentary basins of Australia and their tectonic implications

The stratigraphy, structure and tectonics of Australia's Phanerozoic sedimentary basins are described briefly in terms of three settings: younger internal basins, older internal basins and peripheral basins.The younger internal basins developed successively following part by part cratonization of the Palaeozoic Tasman Fold Belt System. Most of the older internal basins probably had late Proterozoic beginnings and all have Precambrian cratonic basements. The peripheral basins occur around the present continental margins and in New Guinea; the oldest of them may be Devonian.The peripheral basins are the simplest to explain in terms of plate tectonics: some can be related to Australia breaking away from Gondwanaland, others to plate convergence in the east and in New Guinea. An attempt is made to fit the internal basins into a platetectonic geological history.     

Aeromagnetic and gravity features of Gondwana and theirrelation to continental break-up: More pieces,less puzzle

Regional geophysical mapping techniques were initiated for economic exploration about 50 years ago and have now developed a completeness of coverage that can be exploited for geological research over large areas. The main strength of gravity and magnetic anomaly surveys lies in their ability to map ‘basement’ geology below cover. Suitably assembled and imaged at the continental-scale, the data give new insight into the mosaic of terranes that makes up the Precambrian continental crust, and into the margins of Precambrian continental fragments that have often been complicated by prolonged rifting before the onset of the drifting apart of continental fragments. Intrusions such as dykes, dyke swarms and plugs of small areal extent, that are often associated with continental disruption, can also be mapped with new totality. Examples using mainly aeromagnetic mapping are given to support a tight reassembly of the Precambrian crustal fragments of central Gondwana. In this, the outer margins of Precambrian blocks, known or interpreted from geophysical anomaly maps of the presently dispersed continents, are reassembled parallel and at a separation of only 50-80 km, typical of the width of present-day rift valleys. In the future, the wider availability of geophysical mapping data from both continents and oceans, with computer systems to process and interpret them, should contribute to a more fruitful co-operation of geologists and geophysicists in Gondwana research using more complete data coverage.     

Kinematics of the Gondwana basins of peninsular India

The Gondwana successions (1–4 km thick) of peninsular India accumulated in a number of discrete basins during Permo-Triassic period. The basins are typically bounded by faults that developed along Precambrian lineaments during deposition, as well as affected by intrabasinal faults indicating fault-controlled synsedimentary subsidence. The patterns of the intrabasinal faults and their relationships with the respective basin-bounding faults represent both extensional and strike-slip regimes. Field evidence suggests that preferential subsidence in locales of differently oriented discontinuities in the Precambrian basement led to development of Gondwana basins with varying, but mutually compatible, kinematics during a bulk motion, grossly along the present-day E–W direction. The kinematic disparity of the individual basins resulted due to different relative orientations of the basement discontinuities and is illustrated with the help of a simple sandbox model. The regional E–W motion was accommodated by strike-slip motion on the transcontinental fault in the north.     

Phanerozoic evolution of the basins of Northern Egypt and adjacent areas

The results of integrating geological well data and geophysical information from the subsurface of northern Egypt are presented in terms of basin dynamics. Recent biostratigraphic data from wells and scarce outcrops are shown to be critical to an understanding of syndepositional tectonics. Six tectonostratigraphic phases of basin evolution are recognized to span the Phanerozoic. These phases initially record the development of intracratonic subsidence, controlled by deep crustal strike-slip tectonics, as Nubian continental and Tethyan marine influences competed across the northern margin of Gondwanaland. Evidence is also presented for the formation of the present day continental margin to northern Egypt. After a phase of crustal stretching, oceanic rifting focused on the western margin of the Arabian Platform, propagating progressively westwards during the Early-Mid-Jurassic. Thereafter, the effects of passive subsidence on the continental margin were disturbed by discrete phases of intracratonic strike-slip, associated Syrian Arc folding, and the formation of deep basins in the opening Red Sea and Gulf of Suez. Three structural fabrics persisted throughout Phanerozoic basin evolution, the result of repeated extensional reactivation and inheritance from Pan-African basement.     

Tectonic setting of cambrian rifting, volcanism and ophiolite formation in western tasmania

In western Tasmania, small Precambrian regions are surrounded by a ramifying system of troughs filled with Cambrian sedimentary and volcanic rocks, and ophiolite complexes. The volcanic associations include a rift-related olivine tholeiite association, dacite-rhyolite and andesite associations, and a low-Ti, high-Mg andesite-tholeiite ophiolite association, and may have formed during a long-lived period of crustal thinning, punctuated by episodes of crustal rupturing, magmatism, and small scale rifting. Such extensional tectonism could occur in an active continental margin associated with strike-slip faulting of regional scale, and the volcanic associations may together constitute an igneous assemblage characteristic of magmatism in a transcurrent tectonic regime within an active continental margin undergoing break-up.

The western Tasmanian Cambrian palaeogeography and volcanism preserve a transitional stage between the Late Proterozoic Kanmantoo regime of sedimentary basins with little volcanism developed at the rifting margin of the Proterozoic craton, and the tectonic regime of the Palaeozoic Lachlan Fold Belt where the Cambrian volcanic rocks are dominated by island-arc associations and the rift-related olivine tholeiite association is absent. Eastern Australian lithosphere may have grown by the insertion of newly-formed igneous complexes within the stretched and rifted continental margin, as well as by the accretion of “terrenes” and the addition of packets of subduction complexes which developed off-shore.     

Land–ocean tectonics (LOTs) and the associated seismic hazard over the Eastern Continental Margin of India (ECMI)

The South Indian (Peninsular) Shield which includes both the Eastern and Western Continental Margins of India is not as stable as it was originally thought of. The importance of intraplate seismicity within this Shield has recently been realized with some devastating earthquakes that occurred during the last few decades. It is also significant to note that most of the Precambrian tectonic lineaments in this Shield are oriented in either a NW–SE or W–E direction, joining the eastern offshore. In contrast, the western margin has an elevated coast, associated with a linear coast parallel escarpment, particularly on the southern side, superimposed by Deccan Trap volcanics on the northern side. The fault reactivation and the associated seismicity are hence more predominant on the east coast. Recent geophysical studies delineated land–ocean tectonics (LOTs) over the eastern margin, in some cases associated with moderate seismicity as a result of the compressional stress acting on the Indian Plate. Though the Eastern Continental Margin of India (ECMI) is considered as a passive margin, coastal seismicity due to the reactivation of the pre-existing tectonic lineaments extending offshore represents a potential natural hazard. In this context, the ECMI appears to be much more vulnerable compared to its counterpart on the west.     

敦煌复合造山带前寒武纪地质体的组成和演化

敦煌复合造山带位于塔里木克拉通东端,是连接塔里木克拉通和华北克拉通的重要纽带。近年来,敦煌基础地质研究取得了重大进展。本文简要回顾了敦煌基础地质研究历史和现状,系统归纳了区内前寒武纪地质单元时空分布特征及前寒武纪构造-热事件序列,初步讨论了前寒武纪大陆地壳形成和演化规律、前寒武纪结晶基底亲缘性及构造演化过程,提出:(1)敦煌造山带前寒武纪结晶基底形成于ca.3.1~1.6Ga,构造-热事件主要划分为新太古代(ca.2.7~2.6Ga和2.6~2.5Ga)、古元古代晚期(ca.2.0~1.8Ga)和中元古代早期(1.8~1.6Ga)三个阶段;(2)新太古代早期(ca.2.7~2.6Ga)和新太古代晚期(2.6~2.5Ga)是敦煌造山带大陆地壳形成的主要阶段;古元古代晚期(ca.2.0~1.8Ga)和中元古代早期(1.8~1.6Ga)主要是古老大陆地壳物质再循环阶段,也有少量新生陆壳物质的形成;(3)敦煌造山带前寒武纪结晶基底最初拼合事件可能发生在新太古代末期(~2.5Ga),之后经历了古元古代晚期(ca.2.0~1.8Ga)汇聚、碰撞造山过程,直到中元古代早期(1.8~1.6Ga),造山活动结束,前寒武纪结晶基底最终固结,进入稳定发展阶段;(4)前寒武纪结晶基底最终稳定固结之后,即～1.6Ga之后,敦煌前寒武纪结晶基底可能进入长达12亿年的静寂期,一直处于稳定状态,目前没有发现相关的岩浆-变质-沉积记录(类似于地盾状态),直至古生代志留纪开始活化(～440Ma),卷入古亚洲洋南缘俯冲、碰撞造山过程并被强烈改造。     

东南极古陆核的研究现状、问题与设想

东南极地盾(克拉通)中的太古宙陆核主要分布在面向印度洋扇区的内皮尔山、南查尔斯王子山、赖于尔群岛和西福尔丘陵,在面向澳大利亚、非洲和太平洋扇区只零星出露。这些古陆核被早元古代—早古生代(泛非期)造山带所分割,它们具有不同的早期演化历史和后期改造过程,并且产于不同扇区的陆核与相邻冈瓦纳陆块具有密切的亲缘关系。对东南极古陆核开展系统的冰上和冰下地质调查以及岩石地球化学综合研究,查明太古宙岩石(物质)的时空分布、岩石成因、源区性质、构造属性及其变质改造历史,进而构建东南极古大陆从初始成核到最终聚陆的历史框架,这将弥补地球早期演化研究领域的南极短板,同时也必将促进地球早期演化研究领域的发展。      

俄罗斯-蒙古地学断面地壳模型的地质-地球物理资料综合研究

地学断面是指地壳的垂直剖面,主要通过对地质和地球物理资料的综合分析来揭示构造带的性质及其空间关系。横断面的研究所采用的数据基本包括100 km宽区域地质图、上地壳的地质剖面图、重磁图(沿横断面的重磁剖面图)以及地壳的地震波速度、密度和其他地球物理属性的剖面图。这些数据被用于构建综合的数据剖面图(结果图),以展示各种地球动力学条件下(裂谷、海洋、碰撞带、造山盆地、大陆地台和岩浆弧,包括安第斯岛弧、活动大陆边缘、海沟、弧前和弧后盆地)的特定的岩石组构。本项目的研究目标是根据研究区现存的地质和地球物理数据的综合解释,统一图例,建立研究区深部剖面,以确定地体的空间关系及其在板块构造方面的地球动力学性质。 前人已分别对东西伯利亚南部和蒙古境内的多个地体进行了构造划分,并对它们的地球动力学性质和时空关系进行了分析。研究结果显示该系列地体为早古生代、中晚古生代和晚古生代—早中生代的岛弧和微大陆。此外,研究还识别出了中—晚古生代和晚古生代—早中生代安第斯型活动大陆边缘、晚古生代—早中生代被动大陆边缘和早白垩世裂谷。与岛弧和安第斯型活动大陆边缘相关的岩体被推覆至相邻大陆和微陆块上,部分推覆宽度可达150 km。目前已开展泥盆纪到晚侏罗世时期蒙古-鄂霍次克海地区的古地球动力学重建。 “非地槽”型花岗岩类岩浆作用在板块构造方面找到了直接且合理的解释,其中泥盆纪—石炭纪和二叠纪—三叠纪岩浆作用区域对应于安第斯型活动大陆边缘,中—晚侏罗世岩浆作用则与西伯利亚/蒙古-中国大陆板块碰撞有关。碰撞岩浆作用中亚碱性(地幔)元素的存在及其所在的构造区域在很大程度可以说明蒙古-鄂霍次克海闭合后,巨厚大陆岩石圈下曾经发生过持续的大洋裂谷活动(地幔热点)。在早白垩世时期,大陆裂谷活动影响到了同一时期正在发生的大陆汇聚作用。 西伯利亚南部边界大部分具有安第斯型活动大陆边缘性质,这也是蒙古—鄂霍次克缝合线沿线蛇绿岩数量较少的原因。因为当汇聚大陆一个具有安第斯类型的活动边缘,而另一个具有被动边缘时,前者的大陆地壳会最终逆冲到后者之上,并因此破坏掉先前出露的蛇绿杂岩体。部分被破坏的蛇绿岩块是俯冲带保留下来的海山残余,其可能成为增生-俯冲楔体的混沌复合体的一部分。然而,由于快速俯冲作用,这种楔形体在晚二叠世—早侏罗世的积累并不是西伯利亚活动边缘的典型特征。 沿地学断面综合的地质和地球物理资料分析表明,亚洲大陆是在显生宙时期由部分前寒武纪微陆块构造拼贴而成的。前寒武纪地块间存在不同宽度的已变形且剥蚀强烈的显生宙火山弧,它们也被归类为特定地体。     

The Precambrian supercontinent Palaeopangaea: two billion years of quasi-integrity and an appraisal of geological evidence

The Protopangaea-Palaeopangaea model for the Precambrian continental crust predicts quasi-integrity reflecting a dominant Lid Tectonics defined by a palaeomagnetic record showing prolonged near-static polar behaviour during very long time intervals (~2.7–2.2, 1.5–1.2, and 0.75–0.6 Ga). Intervening times show polar loops radiating from the geometric centre of the crust explaining the anomalous Precambrian magnetic inclination bias. The crustal lid was a symmetrical crescent-shaped body confined to a single hemisphere on the globe comparable in form to the Phanerozoic supercontinent (Neo)Pangaea. There were two major transitions in the tectonic regime when prolonged near-static motion was succeeded by widespread tectonic-magmatic activity, and each coincided with the major isotopic/geochemical signatures in the Precambrian record. The first comprised a ~90° reconfiguration of crust and mantle at ~2.2 Ga terminating the long 2.7–2.2 Ga static interval; the second was the largest continental break-up event in geological history and is constrained to the Ediacaran Period at ~0.6 Ga by multiple isotopic and geochemical signatures and the subsidence history of marine passive margins. Break-up of the lid at ~0.6 Ga defines a transition from dominant Lid Tectonics to dominant Plate Tectonics and is the primary cause of contrasts between the Precambrian and Phanerozoic aeons of geological times. The long interval of minimal continental motion in the mid-Proterozoic correlates with extensive emplacement of anorogenic anorthosite-rapakivi plutons unique to these times, and high-level emplacement was probably caused by blanketing of the mantle and comprehensive thermal weakening of the crust. Continental velocities were low during the two Proterozoic intervals characterized by profound glaciation (~2.4–2.2 and ~0.75–0.6 Ga) when partial or complete magmatic shutdown is likely to have reduced volcanic greenhouse gas production. Specific implications of Protopangaea-Palaeopangaea include: (i) support for recent evidence that 60–70% of the present continental crust had accreted by ~2.5 Ga; (ii) recognition from spatially constrained mineral provinces that sub-crustal lithosphere was already chemically differentiated by mid-Archaean times; (iii) strong axial alignment of younger greenstone belts, major Palaeoproterozoic shear zones, and later Meso–Neoproterozoic mobile/orogenic belts; (iv) concentration of anorogenic magmatism and progressive contraction of activity towards the orogenic margin subsequently to become the focus of Grenville (~1.1 Ga) orogenesis; and (v) late Neoproterozoic arc magmatism/tectonics at the instep margin of the continental crescent persisting until the Ediacaran continental break-up.     

Concerning tectonics and the tectonic evolution of the Arctic

The particularities of the current tectonic structure of the Russian part of the Arctic region are discussed with the division into the Barents–Kara and Laptev–Chukchi continental margins. We demonstrate new geological data for the key structures of the Arctic, which are analyzed with consideration of new geophysical data (gravitational and magnetic), including first seismic tomography models for the Arctic. Special attention is given to the New Siberian Islands block, which includes the De Long Islands, where field work took place in 2011. Based on the analysis of the tectonic structure of key units, of new geological and geophysical information and our paleomagnetic data for these units, we considered a series of paleogeodynamic reconstructions for the arctic structures from Late Precambrian to Late Paleozoic. This paper develops the ideas of L.P. Zonenshain and L.M. Natapov on the Precambrian Arctida paleocontinent. We consider its evolution during the Late Precambrian and the entire Paleozoic and conclude that the blocks that parted in the Late Precambrian (Svalbard, Kara, New Siberian, etc.) formed a Late Paleozoic subcontinent, Arctida II, which again “sutured” the continental masses of Laurentia, Siberia, and Baltica, this time, within Pangea.     

青藏高原隆升机制新模式

作为创建大陆动力学理论体系的最佳野外实验室的青藏高原, 涉及当代固体地球科学前沿和热点的许多重大科学问题.迄今为止, 包括板块构造在内的众多模式不能合理地解释青藏高原重要的地质和地球物理现象.本文从下地壳与中上地壳、造山带与沉积盆地的耦合作用出发, 对青藏高原及邻区进行分尺度、分层块、分阶段的构造解析, 提出青藏高原隆升的下地壳层流构造模式, 认为青藏高原地壳增厚和构造隆升是晚新生代由于锡瓦利克盆地、塔里木盆地和四川盆地下地壳的热软化岩石大量流向青藏高原造成的.