India Eurasia Research Articles

Cenozoic extensional stress evolution in North China

Since the beginning of the Cenozoic, north China has been fragmented by intensive intracontinental rifting and extensional tectonics, which resulted in the formation of two extensional domains: the graben systems around the Ordos block in the west and North China Plain in the east. How to link this Cenozoic extensional tectonics to plate kinematics has long been an issue of debate. This paper presents updated results of fault slip data sets collected in different zones in north China and addresses the changes in the direction of extensional stresses over the Cenozoic. A chronology of three successive extensions has been established and provides evidence for constraining the timing and location of either subduction-induced back-arc tectonics along the western Pacific or collision-related extrusion tectonics in Tibet. The oldest NW–SE trending extension occurred concomitantly with the early Tertiary rifting phase, which was initiated in a back-arc setting associated with westward subduction of the Pacific plate under the Asia continent. North China had been subjected, during the Miocene, to regional subsidence with widespread basalt flow, and the direction of extension changed to NE–SW to NNE–SSW, consistent with the spreading direction of the Japan Sea. The dynamic origin of this extension is poorly understood. Since the latest Miocene or earliest Pliocene, north China has been dominated by NW–SE extension resulting in the formation and development of the elongate graben systems around the rigid Ordos block. This extensional phase is accompanied by counterclockwise rotation of blocks such as Ordos, Taihangshan Massif etc., which are bounded to south by the left-lateral strike-slip Qinling fault system. The overall Pliocene-Quaternary deformation in north China accommodates an ESE-ward extrusion of the south China block relative to the Gobi-Mongolia plateau, as the consequence of late-stage India–Eurasia convergence.

Cenozoic deformation history of the Tancheng–Lujiang Fault Zone, north China, and dynamic implications

Abstract Based on a field analysis of slip vectors from Cretaceous and Tertiary rocks and coupled with rift basin analysis in north China, the Cenozoic deformation history of the Tancheng–Lujiang (Tan–Lu) Fault Zone can be divided into three main phases: early Tertiary normal faulting and northwest–southeast extension; Miocene normal faulting and northeast–southwest to north‐northeast–south‐southwest extension; and Quaternary dextral strike–slip faulting and east‐northeast transpression. The early Tertiary extension, which was responsible for rift basin formation in north China, originated from back‐roll mantle convection induced by westward subduction of the Pacific Plate beneath the Asia continent. The Miocene extension occurred possibly in association with the process of the Japan Sea opening. The Quaternary dextral slip was mainly localized along the middle part of the Tan–Lu Fault Zone and resulted from the far‐field effect of the late‐stage India–Eurasia convergence.

Quaternary folding of the eastern Tian Shan, northwest China

The Tian Shan, east–west trending more than 2000 km, is one of most active intracontinental mountain building belts that resulted from India–Eurasia collision during Cenozoic. In this study, Quaternary folding related to intracontinental mountain building of the Tian Shan orogenic belt is documented based on geologic interpretation and analyses of the satellite remote sensing images [Landsat Thematic Mapper (TM)/Enhanced Thematic Mapper (ETM) and India Remote Sensing (IRS) Pan] combined with field geologic and geomorphic observations and seismic reflection profiles. Analyses of spatial–temporal features of Quaternary folded structure indicate that the early Quaternary folds are widely distributed in both piedmont and intermontane basins, whereas the late Quaternary active folds are mainly concentrated on the northern range-fronts. Field observations indicate that Quaternary folds are mainly characterized by fault-related folding. The formation and migration of Quaternary folding are likely related to decollement surfaces beneath the fold-and-fault zone as revealed by seismic reflection profiles. Moreover, analysis of growth strata indicates that the Quaternary folding began in late stage of early Pleistocene (2.1–1.2 Ma). Finally, tectonic evolution model of the Quaternary deformation in the Tian Shan is presented. This model shows that the Quaternary folding and faulting gradually migrate toward the range-fronts due to the continuous compression related to India–Eurasia collision during Quaternary time. As a result, the high topographic relief of the Tian Shan was formed.

An integrated global model of present-day plate motions and plate boundary deformation

In this paper we present a global model (GSRM-1) of both horizontal velocities on the Earth's surface and horizontal strain rates for almost all deforming plate boundary zones. A model strain rate field is obtained jointly with a global velocity field in the process of solving for a global velocity gradient tensor field. In our model we perform a least-squares fit between model velocities and observed geodetic velocities, as well as between model strain rates and observed geological strain rates. Model velocities and strain rates are interpolated over a spherical Earth using bi-cubic Bessel splines. We include 3000 geodetic velocities from 50 different, mostly published, studies. Geological strain rates are obtained for central Asia only and they are inferred from Quaternary fault slip rates. For all areas where no geological information is included a priori constraints are placed on the style and direction (but not magnitude) of the model strain rate field. These constraints are taken from a seismic strain rate field inferred from (normalized) focal mechanisms of shallow earthquakes. We present a global solution of the second invariant of the model strain rate field as well as strain rate solutions for a few selected plate boundary zones. Generally, the strain rate tensor field is consistent with geological and seismological data. With the assumption of plate rigidity for all areas other than the plate boundary zones we also present relative angular velocities for most plate pairs. We find that in general there is a good agreement between the present-day plate motions we obtain and long-term plate motions, but a few significant differences exist. The rotation rates for the Indian, Arabian and Nubian plates relative to Eurasia are 30, 13 and 50 per cent slower than the NUVEL-1A estimate, respectively, and the rotation rate for the Nazca Plate relative to South America is 17 per cent slower. On the other hand, Caribbean–North America motion is 76 per cent faster than the NUVEL-1A estimate. While crustal blocks in the India–Eurasia collision zone move significantly and self-consistently with respect to bounding plates, only a very small motion is predicted between the Nubian and Somalian plates. By integrating plate boundary zone deformation with the traditional modelling of angular velocities of rigid plates we have obtained a model that has already been proven valuable in, for instance, redefining a no-net-rotation model of surface motions and by confirming a global correlation between seismicity rates and tectonic moment rates along subduction zones and within zones of continental deformation.

Geochemistry and tectonomagmatic affinity of the Yungbwa ophiolite, SW Tibet

The Yungbwa ophiolite is a thrust sheet of about 800 km 2 tectonically overlying an Upper Cretaceous melange south of the Indus–Tsangpo Suture Zone in SW Tibet. Both units have been thrust over the sedimentary series of the Tibetan Tethys zone in the course of the India–Eurasia collision. Harzburgite and clinopyroxene-poor lherzolite are the dominant lithologies. Occasional gabbronoritic and basaltic dikes crosscut the mantle tectonites, but plutonic and volcanic sections are notably absent. The majority of basaltic dikes are tholeiitic and similar to N-MORB with respect to LREE depletion, ratios of diagnostic trace elements and Sr and Nd isotope systematics. Sm–Nd isotope data of three tholeiitic samples yielded an isochron age of 147±25 Ma (MSWD=0.59), and an initial ε( t)Nd value of +8.8. In addition, magnesio-hornblende in a tholeiitic basaltic dike yielded a 40Ar/ 39Ar age of 152±33 Ma. The mineral chemistry of the spinel–peridotites is consistent with an origin in a tectonic setting similar to abyssal peridotites. The nearly chondritic initial 187Os/ 188Os value of a Re-poor orthopyroxene concentrate matches the composition of abyssal peridotites. The strongly LREE depleted trace element signature of the peridotite clinopyroxenes resembles that of clinopyroxenes from ocean floor peridotites. The Nd isotopic composition of a clinopyroxene concentrate is extremely depleted ( 143Nd/ 144Nd=0.514420), indicating an early Jurassic time of depletion ( T DM=187 Ma) and suggesting that this clinopyroxene represents residual mantle material. In contrast, the bulk peridotites are characterized by convex-downward REE patterns, coupled with low 143Nd/ 144Nd ratios and elevated 87Sr/ 86Sr ratios. We suggest that these geochemical signatures resulted from secondary processes during or after emplacement of the ophiolite complex.

Late Quaternary right-lateral displacement along active faults in the Yanqi Basin, southeastern Tian Shan, northwest China

Late Quaternary right-lateral displacement and slip rates have been determined along WNW–ESE-trending active faults in the intermontane Yanqi Basin on the southeastern flank of the Chinese Tian Shan. Detailed analyses of satellite images and field investigation have revealed that the active Kaidu River fault zone on the southern margin of the basin is a strike–slip fault zone. Drainage systems incising late Pleistocene–Holocene alluvial fans record between 3 and 250 m dextral offsets and show progressive displacement along the fault zone. Fault scarps developed in the alluvial fans range in height from 1 to 25 m and alternate along the strike of the fault zone from northeast to southwest facing in a left-stepping en echelon pattern. Based on the offset of stream channels, 14C dates of alluvial deposits, and fabrics within fault rocks, we infer that (1) the average right-lateral slip rate is about 8 mm/year, with a vertical component of 1 mm/year, (2) the offset produced by individual seismic faulting event is typically 3–7 m, (3) the average recurrence interval of large seismic events ( M>7) is ca. 500 years, and (4) the most recent movement occurred during the past 2.5 ky in the Kaidu River fault zone. These strike–slip faults represent partitioning of horizontal slip within an otherwise thrust dominated orogen related to the India–Eurasia collision within the Tian Shan during late Quaternary.

Mass accumulation rates in Asia during the Cenozoic

Summary This work establishes estimates of mass accumulation rates in 18 mostly offshore sedimentary basins in Asia since the beginning of the Cenozoic, ≈ 66 Ma. The estimates were derived from isopach maps, cross-sections and drill holes or stratigraphic columns assuming regional similarity of the strata. Average solid phase volumes and accumulation rates were calculated for nine epochs approximately corresponding to geological periods: Palaeocene ( ≈ 66–58 Ma), Eocene ( ≈ 58–37 Ma), Oligocene( ≈ 37–30 and 30–24 Ma), Miocene ( ≈ 24–17, 17–11 and 11–5 Ma), Pliocene ( ≈ 5–2 Ma) and Quaternary ( ≈ 2–0 Ma). These rates shed new light on the geological history of Asia since the onset of the collision of India with Asia ( ≈ 50 Ma). The overall average accumulation rates curve for Asian sedimentary basins since the beginning of the Tertiary shows an exponential form with slow accumulation rates (less than 0.5 × 106 km3 Myr− 1) until the beginning of the Oligocene, more than 15 Myr after the onset of the collision. From the Oligocene onwards rates increase quickly in an exponential manner, reaching their maximum values in the Quaternary (more than 1.5 × 106 km3 Myr− 1). From these observations we suggest that extrusion and crustal shortening are complementary processes that have been successively dominant throughout the India–Eurasia collision history. At smaller scales one may distinguish between independent histories at the subcontinental and basin scales. This permits a comparison of the relative importance of tectonic and climatic erosion processes affecting the different mountain belts of Asia during the Cenozoic.

The Indian Ocean Nodule Field: petrotectonic evolution and ferromanganese deposits

The Indian Ocean Nodule Field (IONF) is significant from several points of view. Roughly bordered by 10°S to 16°30′S and 72°E to 80°E and located within the Central Indian Ocean Basin (CIOB), the field hosts the world's second largest and second high grade manganese nodule deposit, after the equatorial nodule belt in the north Pacific Ocean. Moreover, the crust underlying this field is characterised by unique morphotectonic signatures owing to its formation between 60 and 49 Ma under three variable spreading conditions, fast, intermediate and slow, from the Indian Ocean Ridge System (IORS). The nodule field has been surveyed both extensively (more than 0.4 million km 2 area) and intensively (comprising of a large geophysical data set and geological sample inventory) during the last two decades. Several morphotectonic features, such as seamounts, hills, ridge-normal lineaments and ridge-parallel lineations, have disturbed the apparently smooth topographic gradient (1:7000) of the seafloor here. Variations in the rate of spreading and formation of new oceanic crust along the ridge crest, during more than one episode of India–Eurasia collision, are imprinted in the IONF. Based on the nature of the ridge-parallel lineations, which are related to the rate of crustal accretion, the field is divided in to four sectors: A, B, C, and D, from north to south. Sectors A and C were formed at a fast rate of spreading (90–95 mm/year, half-rate) and sectors B and D were formed at an intermediate (55 mm/year) and slow (26 mm/year) rates, respectively. The predominance of tensional stress in sectors A and C caused asymmetrical flexuring of the seafloor, resulting in widely spaced faults and folds with low amplitude and large wavelength. In contrast, the seafloor flexuring in sector D are closely spaced, long, symmetrical and of high amplitude. The timing and intensity of the collision of India with Eurasia is constrained by the variable intensity of these flexures, suggesting probably a ‘soft’ touch at ∼58 Ma and the hard collision at about 51 Ma. The nodule field hosts several seamounts, both as isolated entities and in linear chains, which are arranged parallel to the flow lines along the direction of absolute motion of the Indian plate. The distribution, morphology and growth patterns of a majority of these seamounts are related to spreading rate, suggesting their formation at the ridge crest. However, many of the seamounts show more than one stage of growth with local intraplate volcanism contributing to the enlargement of the larger ancient seamounts. Varieties of volcanics, such as tholeiitic basalts, spilites, ferrobasalts and pumice, occur within the IONF. The alteration of some of these volcanics has resulted in palagonitisation of the glass and formation of zeolites. Subsequently, during its journey away from the ridge crest to the abyssal areas, the crust underlying the nodule field witnessed intraplate volcanism. This is evident from the addition of younger rocks at the base of the ancient seamounts, inconsistent growth of volcanoes, eruption of ferrobasalt corresponding to the areas of high amplitude magnetic zones and presence of volcanogenic–hydrothermal materials (vhm) of 10 ka age. These findings collectively hint that the IONF is geodynamically unstable and may have been volcanically active in the recent past. During the last 8 Ma, growth of authigenic ferromanganese deposits in the form of manganese nodules and crusts has occurred in the nodule field. The deposits occur at an average water depth of 5000 m. The basinal geomorphology, intraplate tectonic deformations and volcanic eruptions considerably influence the formation, development, morphology, mineralogy and composition of these deposits. The data show that the large seamounts, reverse faults and fracture zones (FZs) supply rock fragments as ‘seeds’ for the nodule formation. The hydrogenous precipitation from the overlying water column is the primary source of metal accumulation in the nodules. The secondary (relatively weak) intraplate eruptions along the base of ancient seamounts or lineaments, subsurface igneous activity and diagenetic remobilisation of metals have also played significant role in the growth and enrichment of the deposit. Based on a large data set, we estimate the contribution of various physico-chemical parameters and model the probable conditions of formation of the ferromanganese deposits in the IONF. The model also hints at the location where the resource exploitation should be rewarding.

Geologic constraints on middle-crustal behavior during broadly synorogenic extension in the central East Greenland Caledonides

Structural and U–Pb geochronologic data from the Forsblad Fjord area of East Greenland (72°30′N) indicate close spatial and temporal ties between orogen-parallel shear and extensional deformation during Caledonian orogenesis. This territory is composed of three tectonostratigraphic units separated by two splays of the Fjord Region Detachment System (FRDS), a principal extensional fault system of the East Greenland Caledonides that was active in Silurian time. The oldest Caledonian fabrics in Forsblad Fjord, which developed at upper amphibolite facies metamorphic conditions, indicate that there was north–south, lateral extrusion of ductile middle-crustal material synchronous with approximately east–west shortening. U–Pb dating of synkinematic granitic leucosomes in migmatitic schists and gneisses demonstrates that this process was underway at ca. 425 Ma. Subsequently, east–west extension along the two splays of the FRDS truncated the older fabrics; the structurally highest of these shear zones – the Tindern detachment – was active as early as ca. 424 Ma. This implies either that there was a rapid transition from Caledonian shortening and possible transpressional deformation to post-orogenic collapse, or our preferred interpretation that extension was synorogenic. The FRDS shares many structural characteristics with the South Tibetan Detachment System of the Cenozoic Himalayan orogen but exhibits two important differences. First, while the South Tibetan system developed in the down-going Indian plate during the India–Eurasia collision, the Fjord Region system developed in the overriding Laurentian plate during the collision of Laurentia with Baltica. Second, whereas the exposed extensional structures in the Himalayas developed in the upper crust and are only inferred to have extended to deeper levels, those in the Forsblad Fjord area were demonstrably active at middle-crustal levels. Evidence for broadly coeval extension and contraction at differen t structural levels in both mountain belts emphasizes the general importance of crustal decoupling in the collisional orogenic process, and implies that synorogenic extensional deformation is not strictly an upper crustal phenomenon.

Late Mesozoic and Cenozoic rifting and its dynamic setting in Eastern China and adjacent areas

During the Late Mesozoic and Cenozoic, extension was widespread in Eastern China and adjacent areas. The first rifting stage spanned in the Late Jurassic–Early Cretaceous times and covered an area of more than 2 million km 2 of NE Asia from the Lake Baikal to the Sikhot-Alin in EW direction and from the Mongol–Okhotsk fold belt to North China in NS direction. This rifting was characterized by intracontinental rifts, volcanic eruptions and transform extension along large-scale strike–slip faults. Based on the magmatic activity, filling sequence of basins, tectonic framework and subsidence analysis of basins, the evolution of this area can be divided into three main developmental phases. The first phase, calc-alkaline volcanics erupted intensely along NNE-trending faults, forming Daxing'anling volcanic belt, NE China. The second phase, Basin and Range type fault basin system bearing coal and oil developed in NE Asia. During the third phase, which was marked by the change from synrifting to thermal subsidence, very thick postrift deposits developed in the Songliao basin (the largest oil basin in NE China). Following uplift and denudation, caused by compressional tectonism in the near end of Cretaceous, a Paleogene rifting stage produced widespread continental rift systems and continental margin basins in Eastern China. These rifted basins were usually filled with several kilometers of alluvial and lacustrine deposits and contain a large amount of fossil fuel resources. Integrated research in most of these rifting basins has shown that the basins are characterized by rapid subsidence, relative high paleo-geothermal history and thinned crust. It is now accepted that the formation of most of these basins was related to a lithospheric extensional regime or dextral transtensional regime. During Neogene time, early Tertiary basins in Eastern China entered a postrifting phase, forming regional downwarping. Basin fills formed in a thermal subsidence period onlapped the fault basin margins and were deposited in a broad downwarped lacustrine depression. At the same time, within plate rifting of the Lake Baikal and Shanxi graben climaxed and spreading of the Japan Sea and South China Sea occurred. Quaternary rifting was marked by basalt eruption and accelerated subsidence in the area of Tertiary rifting. The Okinawa Trough is an active rift involving back-arc extension. Continental rifting and marginal sea opening were clearly developed in various kind of tectonic settings. Three rifting styles, intracontinental rifting within fold belt, intracontinental rifting within craton and continental marginal rifting and spreading, are distinguished on the basis of nature of the basin basement, tectonic location of rifting and relations to large strike–slip faults. Changes of convergence rates of India–Eurasia and Pacific–Eurasia may have caused NW–SE-trending extensional stress field dominating the rifting. Asthenospheric upwelling may have well assisted the rifting process. In this paper, a combination model of interactions between plates and deep process of lithosphere has been proposed to explain the rifting process in East China and adjacent areas. The research on the Late Mesozoic and Cenozoic extensional tectonics of East China and adjacent areas is important because of its utility as an indicator of the dynamic setting and deformational mechanisms involved in stretching Lithosphere. The research also benefits the exploration and development of mineral and energy resources in this area.

Cenozoic episodic volcanism and continental rifting in northeast China and possible link to Japan Sea development as revealed from K–Ar geochronology

Cenozoic volcanic rocks in northeast China comprise part of the volcanic belt of the western circum-Pacific rim and represent one of the presently active tectono-magmatic regions of the world. Over 590 volcanoes with erupted basalts covering an area of ∼50,000 km 2 are exposed in the Songliao graben and particularly on its flanks. K–Ar dating of the volcanic rocks sampled from a selection of eruption sites over the region reveals that the volcanism occurred episodically through the entire Cenozoic corresponding to the tectono-magmatic interactions particularly between the India, Eurasia and Pacific Plates. The volcanism initiated in the Songliao graben in late Cretaceous (∼86 Ma) and migrated flankward since ∼28 Ma. The magmatic propagation shows three major stages intimately associated with the evolution of Japan Sea and related to the geodynamic forcing of the India–Eurasia collision. Prior to Japan Sea rifting, volcanic eruptions were restricted to the Songliao basin. During Japan Sea opening, volcanism migrated into the lateral belts. After cessation of Japan Sea opening at ∼15 Ma, volcanism with greatest intensity occurred on both flanks particularly along the Yi–Yi fault system around 14–13 Ma and subsequently the Fu–Mi fault between 11 and 7 Ma. Continuing this trend of migration, eruptions scattered further away from the Songliao basin in the last 4.5 Ma. We suggest that the Cenozoic volcanic belt in northeast China and the Japan Sea backarc basin are competitive parts in the eastern-marginal magmatic system of the Eurasian Plate. The early stage of the volcanism in the Songliao basin may have resulted from mantle upwelling beneath the Songliao–Bohai basin belt. Rifting of the NE faults and relatively weak intensity of volcanism in northeast China during Japan Sea opening could be attributable to the lithospheric breakup in the Japan Sea and spreading of Japan Sea. The subsequent strong volcanism in northeast China after cessation of the Japan Sea opening implicates the easiest pathway for the melts of the magmatic system in the plate margin. The diversified volcanism in scattered localities during the Quaternary may indicate localized melting processes or notable modifications in smaller sized individual domains and possibly, a magmatically waning phase of the limited source in eastern China.

New space geodetic constraints on the distribution of deformation in Central Asia

Results from repeated measurements across a 90-sites global positioning system network in Central Asia provide direct evidence of current high rates of tectonic deformation far north of the India–Eurasia suture zone. The data help to quantify both the partitioning of deformation within the seismically active Tien Shan and Northern Pamirs, as well as the ongoing rotation of virtually undeformed blocks such as the Tarim with respect to stable Eurasia. The NNW to SSE shortening rates derived from the computations reach values of 23±3 mm yr−1 over the ranges studied, suggesting that regional deformation rates have increased considerably within the study area since the onset of Cenozoic shortening 20–25 Myr ago.

Interaction compression–extension à la limite Mongolie–Sibérie : analyse préliminaire des déformations récentes et actuelles dans le bassin de Tunka

Abstract The Tunka basin was initiated during Oligocene, under transtensional regime (normal-sinistral) as shown by large-scale structures and geomorphology. Nevertheless, a preliminary analysis of the most recent deformations allows us to evidence transpression on several sites within the basin. These tectonic features together with focal mechanisms and preliminary GPS data, suggest that the kinematics of the Tunka basin has undergone a very recent change, which could be due to the northward propagation of the India–Eurasia collisional strain field.

Evolution and hydrocarbon habitat of the South Turgay Basin, Kazakhstan

The South Turgay Basin is a Mesozoic intracontinental rift with a Lower Jurassic to Lower Cretaceous fill. It is underlain by a basement complex comprising Precambrian metamorphics and Palaeozoic carbonates and clastics, and was formed as a result of right lateral movement on the Karatau–Talasso–Fergana Fault. Four principal graben systems are found in the basin. These are the Ariskum, Akshabulak, Sarylan and Bozingen grabens. The graben fill is represented by up to 5 km of dominantly continental sediments, with lacustrine, alluvial and fluvial units, with a series of gross fining-upwards sequences in the Lower to Middle Jurassic (syn-rift) and Upper Jurassic to Lower Cretaceous (post-rift). Marginal marine conditions began to become established during the Apto-Albian with a marine transgression from the west. Tertiary regional uplift resulting from the India–Eurasia collision stripped off later deposits. Recoverable hydrocarbons in the order of 1 billion barrels of oil equivalent have been proven to date in the large Kumkol Field and a number of smaller pools.

Sharks and rays (chondrichthyes) from the Upper Cretaceous red beds of the south-central Pyrenees (Lleida, Spain): indices of an India–Eurasia connection

Six chondrichthyan taxa are recorded in Late Cretaceous (Maastrichtian) red beds of the south-central Pyrenees (Tremp Formation, Lleida, Spain), indicating marine influence in the palaeoenvironment. Two ray species found in Spain have been previously described in India. One ray species conforms to the Gondwanan genus Igdabatis and the endemic Indian species Igdabatis indicus Prasad and Cappetta, 1993 [Prasad, G.V.R., Cappetta, H., 1993. Late Cretaceous selachian from India and the age of the Deccan traps. Palaeontology 36 (1), 231–248.] The other ray from the Tremp Formation is also close to the Indian material assigned to Rhombodus sp. 2. The limited dispersal abilities of benthic rays points to a shallow trans-Tethyan connection between Eurasia and India at the end of the Cretaceous. The data increase the evidence of a biogeographical relationship between Eurasia and Gondwanan continents at the Cretaceous–Tertiary boundary.

Finite element modelling of crustal deformation in the Baikal rift zone: new insights into the active–passive rifting debate

The origin of the forces responsible for crustal extension in the Baikal rift zone, Siberia, is the object of a debate between `passive rifting' models, where crustal extension is primarily caused by horizontal forces related to the kinematics of Asia (India–Eurasia collision), and `active rifting' models, where crustal extension is primarily caused by a diapiric mantle upwelling. In this work, we used a two-dimensional visco-elastic finite element model in order to determine whether horizontal forces alone can account for the present-day deformation in the Baikal rift zone. We tested a number of kinematic boundary conditions and compared predictions of various models against the observed stress and strain field deduced from seismotectonic data (earthquake focal mechanisms and microtectonic analyses). By adjusting the kinematic boundary conditions and using a three-plate model with a differential displacement between the Mongolian and Amurian plates, we found a best-fit model that correctly accounts for the observed strain and stress field over the entire Baikal rift zone. The fact that our model does not take into account vertical forces but still explains most of the observed deformation suggests that the present-day opening of the Baikal rift is essentially controlled by horizontal forces related to the regional kinematics. These forces could have their origin in the India–Eurasia collision zone further south. This result does not imply that the asthenosphere played no role in the rifting process, in particular before the `fast rifting' stage of the Baikal rift evolution (3–4 Ma), but might suggest a recent (Plio–Quaternary) triggering effect of the India–Asia collision on the deformation in the Baikal rift.

Palaeomagnetism, North China and South China collision, and the Tan-Lu fault

Refined Apparent Polar Wander (APW) paths for the North and South China Blocks (ncb and scb) are presented and the collision between the NCB and SCB discussed. We suggest that the amalgamation of the NCB and SCB was completed in the late Triassic-early Jurassic, during the Indosinian Orogeny. This proposed timing is based on an analysis of palaeomagnetic signatures relating to continental collisions, such as the convergence of palaeolatitude, deflections of declination, hairpin-like loops in and superposition of APW paths. Like the Cenozoic India—Eurasia collision, the Mesozoic NCB- SCB collision reactivated ancient faults in eastern China, converting some of them into transcurrent faults, of which the Tan-Lu fault is the most famous.

The tectonic evolution of the Tibetan Plateau

The Tibetan Plateau, between the Kunlun Shan and the Himalayas, consists of terranes accreted successively to Eurasia. The northernmost, the Songban Ganzi Terrane, was accreted to the Kunlun (Tarim-North China Terrane) along the Kunlun-Qinling Suture during the late Permian. The Qiangtang Terrane accreted to the Songban-Ganzi along the Jinsha Suture during the late Triassic or earliest Jurassic, the Lhasa Terrane to the Qiangtang along the Banggong Suture during the late Jurassic and, finally, Peninsular India to the Lhasa Terrane along the Zangbo Suture during the Middle Eocene. The Kunlun Shan, Qiangtang and Lhasa Terranes are all underlain by Precambrian continental crust at least a billion years old. The Qiangtang and Lhasa Terranes came from Gondwanaland. Substantial southward ophiolite obduction occurred across the Lhasa Terrane from the Banggong Suture in the late Jurassic and from the Zangbo Suture in the latest Cretaceous-earliest Palaeocene. Palaeomagnetic data suggest successive wide Palaeotethyan oceans during the late Palaeozoic and early Mesozoic and a Neotethys which was at least 6000 km wide during the mid-Cretaceous. Thickening of the Tibetan crust to almost double the normal thickness occurred by northward-migrating north-south shortening and vertical stretching during the mid-Eocene to earliest Miocene indentation of Asia by India; Neogene strata are almost flat-lying and rest unconformably upon Palaeogene or older strata. Since the early Miocene, the northward motion of India has been accommodated principally by north south shortening both north and south of Tibet. From early Pliocene to the Present, the Tibetan Plateau has risen by about two kilometres and has suffered east-west extension. Little, if any, of the India Eurasia convergence has been accommodated by eastward lateral extrusion.

Palaeomagnetic constraints on Himalayan-Tibetan tectonic evolution

Palaeomagnetic data from the Lhasa, Qiangtang and Kunlun Terranes of the Tibetan Plateau are used with data from stable Eurasia, eastern China and Indochina, to test different models of crustal thickening in the Tibetan Plateau, to attempt a Carboniferous palaeogeographic reconstruction, and to calculate the relative motion between the South China Block and the Indochina Block. The data suggest that since the onset of the India—Eurasia collision, the Lhasa Terrane has moved 2000 + 800 km north with respect to stable Eurasia. This indicates that strong internal defomation must have taken place in southern Eurasia since the collision, and thus challenges the model of large-scale underthrusting of the Indian subcontinent beneath the Tibetan Plateau as the mechanism for crustal thickening in Tibet. Palaeomagnetic results from the Kunlun Terrane show that it was at 22° south latitude during the Carboniferous. A Carboniferous reconstruction is presented in which the Kunlun and Qiangtang Terranes, several Indochina terranes, and the North and South China Blocks are grouped together. These units of continental crust all share the specific tropical and subtropical Cathaysian flora, and the group is therefore called the Cathaysian composite continent. To test the model of propagating extrusion tectonics, we have used newly available palaeomagnetic results from South China and Indochina to calculate probable displacements. This exercise suggests a rotation of about 8° of Indochina with respect to the South China Block that is smaller than the predicted rotation of 40°, A large eastward translation of the South China Block relative to the Indochina Block of about 1500 km is consistent with the palaeomagnetic data.

India–Eurasia collision chronology

India–Eurasia collision chronology