Early Cretaceous Tectonics and Evolution of the Tibetan Plateau

Selected geological data on Early Cretaceous strata, structures, magmatic plutons and volcanic rocks from the Kunlun to Himalaya Mountains reveal a new view of the Early Cretaceous paleo-tectonics and the related geodynamic movement of the Tibetan Plateau. Two major paleo-oceans, the Mid-Tethys Ocean between the Qiangtang and Lhasa blocks, and the Neo-Tethys Ocean between the Lhasa and Himalayan blocks, existed in the Tibetan region in the Early Cretaceous. The Himalayan Marginal and South Lhasa Seas formed in the southern and northern margins of the Neo-Tethys Ocean, the Central Tibet Sea and the Qiangtang Marginal Sea formed in the southern and northern margins of the Mid-Tethys Ocean, respectively. An arm of the sea extended into the southwestern Tarim basin in the Early Cretaceous. Early Cretaceous intensive thrusting, magmatic emplacement and volcanic eruptions occurred in the central and northern Lhasa Block, while strike-slip formed along the Hoh-Xil and South Kunlun Faults in the northern Tibetan region. Early Cretaceous tectonics together with magmatic K2O geochemistry indicate an Early Cretaceous southward subduction of the Mid-Tethys Oceanic Plate along the Bangoin-Nujiang Suture which was thrust ~87 km southward during the Late Cretaceous-Early Cenozoic. No intensive thrust and magmatic emplacement occurred in the Early Cretaceous in the Himalayan and southern Lhasa Blocks, indicating that the spreading Neo-Tethys Oceanic Plate had not been subducted in the Early Cretaceous. To the north, terrestrial basins of red-beds formed in the Hoh-Xil, Kunlun, Qilian and the northeastern Tarim blocks in Early Cretaceous, and the Qiangtang Marginal Sea disappeared after the Qiangtang Block uplifted in the late Early Cretaceous.     

Tectonic evaluation of the Indochina Block during Jurassic-Cretaceous from palaeomagnetic results of Mesozoic redbeds in central and southern Lao PDR

Rock magnetic and palaeomagnetic studies were performed on Mesozoic redbeds collected from the central and southern Laos, the northeastern and the eastern parts of the Khorat Plateau on the Indochina Block. Totally 606 samples from 56 sites were sampled and standard palaeomagnetic experiments were made on them. Positive fold tests are demonstrated for redbeds of Lower and Upper Cretaceous, while insignificant fold test is resulted for Lower Jurassic redbeds. The remanence carrying minerals defined from thermomagnetic measurement, AF and Thermal demagnetizations and back-field IRM measurements are both magnetite and hematite. The positive fold test argues that the remanent magnetization of magnetite or titanomagnetite and hematite in the redbeds is the primary and occurred before folding. The mean palaeomagnetic poles for Lower Jurassic, Lower Cretaceous, and Upper Cretaceous are defined at Plat./Plon. = 56.0°N/178.5°E (A₉₅ = 2.6°), 63. 3°N/170.2°E (A₉₅ = 6.9°), and 67.0°N/180.8°E (A₉₅ = 4.9°), respectively. Our palaeomagnetic results indicate a latitudinal translations (clockwise rotations) of the Indochina Block with respect to the South China Block of −10.8 ± 8.8° (16.4 ± 9.0°); −11.1 ± 6.2° (17.8 ± 6.8°); and −5.3 ± 4.7° (13.3 ± 5.0°), for Lower Jurassic, Lower Cretaceous, and Upper Cretaceous, respectively. These results indicate a latitudinal movement of the Indochina Block of about 5–11° (translation of about 750–1700 km in the southeastward direction along the Red River Fault) and clockwise rotation of 13–18° with respect to the South China Block. The estimated palaeoposition of the Khorat Plateau at ca. 21–26°N during Jurassic to Cretaceous argues for a close relation to the Sichuan Basin in the southwest of South China Block. These results confirm that the central part of the Indochina Block has acted like a rigid plate since Jurassic time and the results also support an earlier extrusion model for Indochina.     

Paleomagnetism of the Upper Cretaceous red-beds from the eastern edge of the Lhasa Terrane: New constraints on the onset of the India-Eurasia collision and latitudinal crustal shortening in southern Eurasia

The Late Cretaceous location of the Lhasa Terrane is important for constraining the onset of India-Eurasia collision. However, the Late Cretaceous paleolatitude of the Lhasa Terrane is controversial. A primary magnetic component was isolated between 580 °C and 695 °C from Upper Cretaceous Jingzhushan Formation red-beds in the Dingqing area, in the northeastern edge of the Lhasa Terrane, Tibetan Plateau. The tilt-corrected site-mean direction is D_s/I_s = 0.9°/24.3°, k = 46.8, α₉₅ = 5.6°, corresponding to a pole of Plat./Plon. = 71.4°/273.1°, with A₉₅ = 5.2°. The anisotropy-based inclination shallowing test of Hodych and Buchan (1994) demonstrates that inclination bias is not present in the Jingzhushan Formation. The Cretaceous and Paleogene poles of the Lhasa Terrane were filtered strictly based on the inclination shallowing test of red-beds and potential remagnetization of volcanic rocks. The summarized poles show that the Lhasa Terrane was situated at a paleolatitude of 13.2° ± 8.6°N in the Early Cretaceous, 10.8° ± 6.7°N in the Late Cretaceous and 15.2° ± 5.0°N in the Paleogene (reference point: 29.0°N, 87.5°E). The Late Cretaceous paleolatitude of the Lhasa Terrane (10.8° ± 6.7°N) represented the southern margin of Eurasia prior to the collision of India-Eurasia. Comparisons with the Late Cretaceous to Paleogene poles of the Tethyan Himalaya, and the 60 Ma reference pole of East Asia indicate that the initial collision of India-Eurasia occurred at the paleolatitude of 10.8° ± 6.7°N, since 60.5 ± 1.5 Ma (reference point: 29.0°N, 87.5°E), and subsequently ~ 1300 ± 910 km post-collision latitudinal crustal convergence occurred across the Tibet. The vast majority of post-collision crustal convergence was accommodated by the Cenozoic folding and thrust faulting across south Eurasia.     

柴达木地块与喜马拉雅地体间早白垩世以来南北向缩短量的估算

根据古地磁数据,笔者计算了柴达木地块和喜马拉雅地体早白垩世以来的南北向运移量和其间的南北向距离缩短量,结果表明：①早白垩世后喜马拉雅地体快速向北运移,其运移在于柴达木木地块同时期的运移速率,早白垩以来,两者间南北向距离总计缩短了约５５２２ｋｍ;②印度地块与欧亚大陆自５０Ｍａ碰撞以来,柴达木地块与喜马拉雅地体间南北向上陆壳缩短了约１３６４ｋｍ,这一缩短量支持青藏高原隆升的“挤压、缩短、增厚”模式;③     

Early Carboniferous paleomagnetic results from the northeastern margin of the Qinghai–Tibetan plateau and their implications

We conducted paleomagnetic investigations on limestone from the Lower Carboniferous Huaitoutala Formation in the Qaidam Basin near Delingha City, Qinghai Province, China. The characteristic remanent magnetization (D = 5.8°, I = − 25.7°, k = 114.3, α₉₅ = 4.8°) passes a fold test and indicates a paleopole position of − 39.2°N, 90.4°E and a paleolatitude of 13.5°N for the Qaidam Block for the early Carboniferous. Based on global tectonic reconstructions and paleontological evidence, we suggest that the Qaidam Block was adjacent to, but independent from, the North China, South China, Alashan–Hexi and Tarim blocks at this time. This result suggests that Pre-Carboniferous sutures reported around the Qaidam Basin represent collisional events within Gondwana, rather than the final sutures that gave rise to the present tectonic configuration.     

Metamorphism and tectonic evolution of the Lhasa terrane,Central Tibet

The Lhasa terrane in southern Tibet is composed of Precambrian crystalline basement, Paleozoic to Mesozoic sedimentary strata and Paleozoic to Cenozoic magmatic rocks. This terrane has long been accepted as the last crustal block to be accreted with Eurasia prior to its collision with the northward drifting Indian continent in the Cenozoic. Thus, the Lhasa terrane is the key for revealing the origin and evolutionary history of the Himalayan–Tibetan orogen. Although previous models on the tectonic development of the orogen have much evidence from the Lhasa terrane, the metamorphic history of this terrane was rarely considered. This paper provides an overview of the temporal and spatial characteristics of metamorphism in the Lhasa terrane based mostly on the recent results from our group, and evaluates the geodynamic settings and tectonic significance. The Lhasa terrane experienced multistage metamorphism, including the Neoproterozoic and Late Paleozoic HP metamorphism in the oceanic subduction realm, the Early Paleozoic and Early Mesozoic MP metamorphism in the continent–continent collisional zone, the Late Cretaceous HT/MP metamorphism in the mid-oceanic ridge subduction zone, and two stages of Cenozoic MP metamorphism in the thickened crust above the continental subduction zone. These metamorphic and associated magmatic events reveal that the Lhasa terrane experienced a complex tectonic evolution from the Neoproterozoic to Cenozoic. The main conclusions arising from our synthesis are as follows: (1) The Lhasa block consists of the North and South Lhasa terranes, separated by the Paleo-Tethys Ocean and the subsequent Late Paleozoic suture zone. (2) The crystalline basement of the North Lhasa terrane includes Neoproterozoic oceanic crustal rocks, representing probably the remnants of the Mozambique Ocean derived from the break-up of the Rodinia supercontinent. (3) The oceanic crustal basement of North Lhasa witnessed a Late Cryogenian (~ 650 Ma) HP metamorphism and an Early Paleozoic (~ 485 Ma) MP metamorphism in the subduction realm associated with the closure of the Mozambique Ocean and the final amalgamation of Eastern and Western Gondwana, suggesting that the North Lhasa terrane might have been partly derived from the northern segment of the East African Orogen. (4) The northern margin of Indian continent, including the North and South Lhasa, and Qiangtang terranes, experienced Early Paleozoic magmatism, indicating an Andean-type orogeny that resulted from the subduction of the Proto-Tethys Ocean after the final amalgamation of Gondwana. (5) The Lhasa and Qiangtang terranes witnessed Middle Paleozoic (~ 360 Ma) magmatism, suggesting an Andean-type orogeny derived from the subduction of the Paleo-Tethys Ocean. (6) The closure of Paleo-Tethys Ocean between the North and South Lhasa terranes and subsequent terrane collision resulted in the formation of Late Permian (~ 260 Ma) HP metamorphic belt and Triassic (220 Ma) MP metamorphic belt. (7) The South Lhasa terrane experienced Late Cretaceous (~ 90 Ma) Andean-type orogeny, characterized by the regional HT/MP metamorphism and coeval intrusion of the voluminous Gangdese batholith during the northward subduction of the Neo-Tethyan Ocean. (8) During the Early Cenozoic (55–45 Ma), the continent–continent collisional orogeny has led to the thickened crust of the South Lhasa terrane experiencing MP amphibolite-facies metamorphism and syn-collisional magmatism. (9) Following the continuous continent convergence, the South Lhasa terrane also experienced MP metamorphism during Late Eocene (40–30 Ma). (10) During Mesozoic and Cenozoic, two different stages of paired metamorphic belts were formed in the oceanic or continental subduction zones and the middle and lower crust of the hanging wall of the subduction zone. The tectonic imprints from the Lhasa terrane provide excellent examples for understanding metamorphic processes and geodynamics at convergent plate boundaries.     

Tectono-magmatic evolution of Late Jurassic to Early Cretaceous granitoids in the west central Lhasa subterrane,Tibet

There is ongoing debate as to the subduction direction of the Bangong–Nujiang Ocean during the Mesozoic (northward, southward or bidirectional subduction). Arc-related intermediate to felsic intrusions could mark the location of the subduction zone and, more importantly, elucidate the dominant geodynamic processes. We report whole rock geochemical and zircon U–Pb and Hf isotopic data for granitoids from the west central Lhasa subterrane (E80° to E86°). All rocks show metaluminous to peraluminous, calc-alkaline signatures, with strong depletion of Nb, Ta and Ti, enrichment of large ion lithophile elements (e.g., Cs, Rb, K), a negative correlation between SiO₂ and P₂O₅, and a positive correlation between Rb and Th. All these features are indicative of I-type arc magmatism. New zircon U–Pb results, together with data from the literature, indicate continuous magmatism from the Late Jurassic to the Early Cretaceous (160 to 130 Ma). Zircon U–Pb ages for samples from the northern part of the west central Lhasa subterrane (E80° to E82°30′) yielded formation ages of 165 to 150 Ma, whereas ages of 142 to 130 Ma were obtained on samples from the south. This suggests flat or low-angle subduction of the Bangong–Nujiang Ocean, consistent with a slight southward decrease in zircon εHf(t) values for Late Jurassic rocks. Considering the crustal shortening, the distance from the Bangong–Nujiang suture zone, and a typical subduction zone melting depth of ~ 100 km, the subduction angle was less than 14° for Late Jurassic magmatism in the central Lhasa interior, consistent with flat or low-angle subduction. Compared with Late Jurassic rocks (main εHf(t) values of − 16 to − 7), Early Cretaceous rocks (145 to 130 Ma) show markedly higher εHf(t) values (mainly − 8 to 0), possibly indicating slab roll-back, likely caused by slab foundering or break-off. Combined with previously published works on arc magmatism in the central Lhasa and west part of the southern Qiangtang subterranes, our results support the bidirectional subduction of the Bangong–Nujiang Ocean along the Bangong–Nujiang Suture Zone, and indicates flat or low-angle southward subduction (165 to 145 Ma) followed by slab roll-back (145 to 130 Ma).     

Present-day crustal motion around the Pamir Plateau from GPS measurements

We have used geodetic techniques to improve constraints on the crustal motion of the Pamir Plateau. Three campaigns of Global Position System data acquisition between 2011 and 2015 demonstrate that, in association with the India–Asia collision, a complex pattern of crustal motion exists in the Pamir Plateau. In a north–south direction from the Indian Plate to the Hazak Block, the crust has absorbed ~ 35 mm/yr of shortening, of which ~ 35% is distributed around the Hindu Kush region (~ 12 mm/yr), and another ~ 35% is taken up around the Alai Valley (also ~ 12 mm/yr). Global Position System measurements also show ~ 5 mm/yr of shortening between the Pamir Plateau and the Tajik Basin, whereas between the Pamir and the Tarim Basin, an ~ 10 mm/yr extension rate is observed. With respect to the stable Eurasian Plate, the Pamir rotates counterclockwise at a rate of ~ 1.822°Myr^− 1, with an Euler pole positioned about the west end of the Tajik Basin (37.03 ± 0.74°N, 65.89 ± 0.12°E). The strain rate field calculated from Global Position System velocities reveals that the crustal motion is consistent with localized deformation around the Hindu Kush and the Alai Valley, the latter representing a zone with strong shallow seismic activity.     

New Precambrian palaeomagnetic constraints on the position of the North China Block in Rodinia

We report new palaeomagnetic results from a ca. 1300 to 800 Ma continental shelf succession on the southern margin of the North China Block. A total of 386 oriented core samples were subjected to stepwise demagnetisation. Two overprint components (‘A’ and ‘B’) were identified, with ‘A’ being a Recent geomagnetic field component and ‘B’ a likely Mesozoic remagnetisation related to collision of the North and South China Blocks. An interpreted primary remanence was isolated from six rock units. The most reliable results are as follow, in the order of stratigraphic ascendance. (1) Purple mudstone, muddy sandstone and andesite of the lower Yunmenshan Formation (Rb–Sr age ca. 1270 Ma) yields a high-temperature component that passes both reversal and fold tests and gives a palaeopole at (60.6°S, 87.0°E, A₉₅ = 3.7°). (2) Mudstone in the overlying Baicaoping Formation yields a high-temperature component with a palaeopole at (43.0°S, 143.8°E, A₉₅ = 11.1°). (3) Purple sandstone of the earliest Neoproterozoic Cuizhuang and Sanjiaotang Formations exhibits a high-temperature component that provides a palaeopole at (41.0°S, 44.8°E, A₉₅ = 11.3°). Based on both our new results and a critical selection of available palaeomagnetic data, we construct a preliminary apparent polar wander path (APWP) for the North China Block between 1300 and 510 Ma. Regardless of alternative polarity options applicable to these poles, North China was located within equatorial latitudes for much of this interval. Comparing the North China poles with coeval poles from Laurentia suggests that the two continents were situated on the same plate between 1200 and 700 Ma. North China was thus likely part of the supercontinent Rodinia. Separation of North China and Laurentia occurred between 650 and 615 Ma.     

Cooling history and tectonic exhumation stages of the south-central Tibetan Plateau (China): Constrained by 40Ar/39Ar and apatite fission track thermochronology

Between the Qiangtang Block and Yalung-Zangpo Suture Zone in the south-central Tibetan Plateau, the following geological units and suture zones have been identified from south to north: the Gangdese Granitic Belt, the Lhasa Block, the Nyainqentanghla Shear Zone, the Dangxiong–Sangxiong Tectono-granitic Belt and the Bangong–Nujiang Suture Zone. To better constrain the tectonic evolution and cooling histories of these units, ⁴⁰Ar/³⁹Ar muscovite, biotite and K-feldspar, as well as apatite fission track dating and thermochronological analysis have been carried out. The analytical results indicate that the south-central Tibetan Plateau, with the exception of the Nyainqentanghla Shear Zone, provides a record of three cooling stages at 165–150, 130–110 and ∼45–35 Ma. Fission-track data modelling also indicates that the stages of cooling were different in the different tectonic belts or blocks. Very different cooling phases occurred in the south-central Tibetan Plateau, compared with southern Tibet, as well as along the Yalung–Zangpo Suture Zone. There is no thermochronological evidence to indicate that the south-central part of Tibetan Plateau was influenced by the underthrusting of Indian Plate.The three-stage cooling history and the stages of tectonic exhumation were controlled completely by the closure of the Bangong–Nujiang Suture Zone along its eastern segment during Middle–Late Jurassic (165–150 Ma) and its western segment in the Early–Late Cretaceous (130–110 Ma), as well as by the collision between the Indian and Asian plates in the Paleogene (45–35 Ma).     

Paleomagnetism of the Middle–Late Jurassic to Cretaceous red beds from the Peninsular Thailand: Implications for collision tectonics

Jurassic to Cretaceous red sandstones were sampled at 33 sites from the Khlong Min and Lam Thap formations of the Trang Syncline (7.6°N, 99.6°E), the Peninsular Thailand. Rock magnetic experiments generally revealed hematite as a carrier of natural remanent magnetization. Stepwise thermal demagnetization isolates remanent components with unblocking temperatures of 620–690 °C. An easterly deflected declination (D = 31.1°, I = 12.2°, α₉₅ = 13.9°, N = 9, in stratigraphic coordinates) is observed as pre-folding remanent magnetization from North Trang Syncline, whereas westerly deflected declination (D = 342.8°, I = 22.3°, α₉₅ = 12.7°, N = 13 in geographic coordinates) appears in the post-folding remanent magnetization from West Trang Syncline. These observations suggest an occurrence of two opposite tectonic rotations in the Trang area, which as a part of Thai–Malay Peninsula received clockwise rotation after Jurassic together with Shan-Thai and Indochina blocks. Between the Late Cretaceous and Middle Miocene, this area as a part of southern Sundaland Block experienced up to 24.5° ± 11.5° counter-clockwise rotation with respect to South China Block. This post-Cretaceous tectonic rotation in Trang area is considered as a part of large scale counter-clockwise rotation experienced by the southern Sundaland Block (including the Peninsular Malaysia, Borneo and south Sulawesi areas) as a result of Australian Plate collision with southeast Asia. Within the framework of Sundaland Block, the northern boundary of counter-clockwise rotated zone lies between the Trang area and the Khorat Basin.     

Changes of Late Mesozoic Tectonic Regimes around the Ordos Basin (North China) and their Geodynamic Implications

A synthesis is given in this paper on late Mesozoic deformation pattern in the zones around the Ordos Basin based on lithostratigraphic and structural analyses. A relative chronology of the late Mesozoic tectonic stress evolution was established from the field analyses of fault kinematics and constrained by stratigraphic contact relationships. The results show alternation of tectonic compressional and extensional regimes. The Ordos Basin and its surroundings were in weak N-S to NNE-SSW extension during the Early to Middle Jurassic, which reactivated E-W-trending basement fractures. The tectonic regime changed to a multi-directional compressional one during the Late Jurassic, which resulted in crustal shortening deformation along the marginal zones of the Ordos Basin. Then it changed to an extensional one during the Early Cretaceous, which rifted the western, northwestern and southeastern margins of the Ordos Basin. A NW-SE compression occurred during the Late Cretaceous and caused the termination of sedimentation and uplift of the Ordos Basin. This phased evolution of the late Mesozoic tectonic stress regimes and associated deformation pattern around the Ordos Basin best records the changes in regional geodynamic settings in East Asia, from the Early to Middle Jurassic post-orogenic extension following the Triassic collision between the North and South China Blocks, to the Late Jurassic multi-directional compressions produced by synchronous convergence of the three plates (the Siberian Plate to the north, Paleo-Pacific Plate to the east and Lhasa Block to the west) towards the East Asian continent. Early Cretaceous extension might be the response to collapse and lithospheric thinning of the North China Craton.     

Paleomagnetic versus GPS determined tectonic rotation around eastern Himalayan syntaxis in East Asia

Northward indentation of the Indian Plate has brought about significant tectonic deformation into East Asia. A record of long-term tectonic deformation in this area for the past 50 M yr, particularly the vertical axis rotation, is available through paleomagnetic data. In order to depict rotational deformation in this area with respect to Eurasia, we compiled reliable paleomagnetic data sets from 79 localities distributed around eastern Himalayan syntaxis in East Asia. This record delineates that a zone affected by clockwise rotational deformation extends from the southern tip of the Chuan Dian Fragment to as far as the northwestern part of the Indochina Peninsula. A limited zone that experienced a significant amount of clockwise rotation after an initial India–Asia collision is now located at 23.5°N, 101°E, far away from an area (27.5°N, 95.5°E) where an intense rotational motion has been viewed by a snapshot of GPS measurements. This discrepancy in clockwise rotated positions is attributed to southeastward extrusion of the tectonic blocks within East Asia as a result of ongoing indentation of the Indian Plate. A quantitative comparison between the GPS and paleomagnetically determined clockwise rotation further suggests that following an initial India–Asia collision the crust at 30°N, 94°E paleoposition was subjected to southeastward displacement together with clockwise rotation, which eventually reached to present-day position of 23.5°N, 101°E, implying a crustal displacement of about 1000 km during the past 50 M yr.     

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.     

First Triassic palaeomagnetic constraints from Junggar (NW China) and their implications for the Mesozoic tectonics in Central Asia

Northwestern China belts result from the Palaeozoic collage of Central Asia and the subsequent reactivations due to far-field effects of the Mesozoic Tibetan and the Cenozoic Himalayan collisions. Triassic is a crucial period to understand and decipher the tectonics related to these two episodes. About 250 oriented palaeomagnetic cores from 43 sites were collected from six sections of Upper Permian to Late Triassic sandstone, in South and West Junggar, Northwestern China. Thermomagnetic, IRM and hysteresis measurements reveal magnetite as the main carrier of the magnetic remanence with minor hematite and maghemite. Stepwise thermal demagnetisation has generally isolated two components. The low temperature component, up to 300–350 °C, displays a direction consistent with the present-day geomagnetic field. The locality-mean directions related to the high temperature component (above 350 °C) were also calculated. Two out of six sections display intense viscous magnetisation and the occurrence of maghemite reveals a possible Cenozoic chemical remagnetisation for these two localities. For the other four localities, we assume that the magnetisation is primary because: (1) AMS measurements reveal a primary fabric, (2) there are local occurrences of antipodal polarities, and (3) palaeolatitudes of tilt-corrected poles are compatible with previous studies. The consistency between the Early Triassic poles of West and South Junggar indicates that Junggar evolved as a rigid block only since Early Mesozoic. The comparison of the Late Palaeozoic and the Early Mesozoic poles of Junggar and those of Siberia and Tarim shows major rotations between the Late Permian and the Late Jurassic–Early Cretaceous. These periods of discrete rotations are characterized by strike-slip faulting in Tianshan and Altai and they may correlate with the major episodes of coarse-grained detrital sedimentation and uplift of the range. Especially, the counter-clockwise rotations of Junggar relative to Tarim and Siberia, which occurred between the Early and the Late Triassic and between the Late Triassic and the Late Jurassic, are accommodated by transpressive tectonics in the Tianshan and the Altai belts. This reactivation is a far-field effect of Tibetan blocks diachronous collisions. Therefore, these first Triassic palaeomagnetic results from Junggar infer that post-Carboniferous rotations were due to the combined effect of the post-orogenic transcurrent movement and the Mesozoic oblique reactivation.     

Tectonics of the Afar Depression: A review and synthesis

This article outlines geomorphological and tectonic elements of the Afar Depression, and discusses its evolution. A combination of far-field stress, due to the convergence of the Eurasian and Arabian plates along the Zagros Orogenic Front, and uplift of the Afar Dome due to a rising mantle plume reinforced each other to break the lithosphere of the Arabian–Nubian Shield. Thermal anomalies beneath the Arabian–Nubian Shield in the range of 150 °C–200 °C, induced by a rising plume that mechanically and thermally eroded the base of the mantle lithosphere and generated pulses of prodigious flood basalt since ∼30 Ma. Subsequent to the stretching and thinning the Afar Dome subsided to form the Afar Depression. The fragmentation of the Arabian–Nubian Shield led to the separation of the Nubian, Arabian and Somalian Plates along the Gulf of Aden, the Red Sea and the Main Ethiopian Rift. The rotation of the intervening Danakil, East-Central, and Ali-Sabieh Blocks defined major structural trends in the Afar Depression. The Danakil Block severed from the Nubian plate at ∼20 Ma, rotated anti-clockwise, translated from lower latitude and successively moved north, left-laterally with respect to Nubia. The westward propagating Gulf of Aden rift breached the Danakil Block from the Ali-Sabieh Block at ∼2 Ma and proceeded along the Gulf of Tajura into the Afar Depression. The propagation and overlap of the Red Sea and the Gulf of Aden along the Manda Hararo–Gobaad and Asal–Manda Inakir rifts caused clockwise rotation of the East-Central Block. Faulting and rifting in the southern Red Sea, western Gulf of Aden and northern Main Ethiopian Rift superimposed on Afar. The Afar Depression initiated as diffused extension due to far-field stress and area increase over a dome elevated by a rising plume. With time, the lithospheric extension intensified, nucleated in weak zones, and developed into incipient spreading centers.     

柴达木盆地东段中、新生代沉积迁移规律及原型盆地性质研究

为明确柴达木盆地东段中、新生代沉积迁移变化及原型盆地性质,通过对柴达木盆地东段红山、霍布逊凹陷中、新生界野外地质露头追踪、钻井（孔）资料分析、岩性岩相分析、二维地震剖面解释、地层划分对比及平衡地质剖面恢复的研究,认为中、新生代沉积迁移呈现出形象的“跷跷板”移动现象,这种现象与凹陷所处的大地构造位置、盆地性质及板块运动的远程效应有关。下侏罗统局限于红山小型断陷盆地,中侏罗统范围向南扩大到霍布逊凹陷,与羌塘板块、拉萨地块与亚欧板块两次俯冲挤压碰撞之间的应力松弛作用有关,此作用在早侏罗世导致北部红山地区的板缘裂陷,在中侏罗世扩展到南部的霍布逊地区;晚侏罗世和早白垩世沉积中心位于红山挤压型盆地,这与拉萨地块与欧亚板块碰撞的远程效应导致柴北缘地区构造反转有关;古近系在北部红山凹陷的发育而在南部霍布逊凹陷的缺失,与新特提斯洋东部闭合首先导致霍布逊地区隆升有关;新近系及第四系主要分布在南部霍布逊凹陷,与此时柴北缘及周缘山系全面隆升导致沉积中心南移有关。     

Linking the Tengchong Terrane in SW Yunnan with the Lhasa Terrane in southern Tibet through magmatic correlation

New zircon U–Pb data, along with the data reported in the literature, reveal five phases of magmatic activity in the Tengchong Terrane since the Early Paleozoic with spatial and temporal variations summarized as Cambrian–Ordovician (500–460 Ma) to the east, minor Triassic (245–206 Ma) in the east and west, abundant Early Cretaceous (131–114 Ma) in the east, extensive Late Cretaceous (77–65 Ma) in the central region, and Paleocene–Eocene (65–49 Ma) in the central and western Tengchong Terrane, in which the Cretaceous–Eocene magmatism migrated from east to west. The increased zircon ε_Hf(t) of the Early Cretaceous granitoids from − 12.3 to − 1.4 at ca. 131–122 Ma to − 4.6 to + 7.1 at ca. 122–114 Ma, identified for the first time in this study, and the magmatic flare-up at ca. 53 Ma in the central and western Tengchong Terrane indicate increased contributions from mantle- or juvenile crust-derived components. The spatial and temporal variations and changing magmatic compositions over time in the Tengchong Terrane closely resemble those of the Lhasa Terrane in southern Tibet. Such similarities, together with the data of stratigraphy and paleobiogeography, enable us to propose that the Tengchong Terrane in SW Yunnan is most likely linked with the Lhasa Terrane in southern Tibet, both of which experienced similar tectonomagmatic histories since the Early Paleozoic.     

关于雅鲁藏布江缝合带(东段)的新认识

国内外不少地质学家大都将雅鲁藏布江蛇绿岩带视为印度板块与亚洲板块之间的缝合带。但是,笔者等在喜玛拉雅造山带的东段即仁布-康马一线以东地区的研究却发现,在雅鲁藏布江蛇绿岩带的南侧发育着一个宽大的增生杂岩体,它与雅江蛇绿岩是同一大洋即特提斯喜玛拉雅洋俯冲消减的产物,前者代表着特提斯喜玛拉雅洋消亡遗迹的主体,是印度板块与拉萨地块之间缝合带的主要组成部分;而后者代表的是俯冲带与拉萨地块之间的残余洋壳,它由北向南仰冲,构成日喀则-桑日弧前盆地前缘脊和南部基底,因而其不代表主缝合带。北喜玛拉雅增生杂岩体的发现改变了以Gansser(1964)为代表提出的喜玛拉雅造山带的构造模式,为重新审视印度板块与拉萨地块缝合作用过程提供了一个重要的地质制约和新的研究途径。     

Combined paleomagnetic and geochronological study on Cretaceous strata of the Qiangtang terrane,central Tibet

A combined paleomagnetic and geochronological investigation has been performed on Cretaceous rocks in southern Qiangtang terrane (32.5°N, 84.3°E), near Gerze, central Tibetan Plateau. A total of 14 sites of volcanic rocks and 22 sites of red beds have been sampled. Our new U–Pb geochronologic study of zircons dates the volcanic rocks at 103.8 ± 0.46 Ma (Early Cretaceous) while the red beds belong to the Late Cretaceous. Rock magnetic experiments suggest that magnetite and hematite are the main magnetic carriers. After removing a low temperature component of viscous magnetic remanence, stable characteristic remanent magnetization (ChRM) was isolated successfully from all the sites by stepwise thermal demagnetization. The tilt-corrected mean direction from the 14 lava sites is D = 348.0°, I = 47.3°, k = 51.0, α₉₅ = 5.6°, corresponding to a paleopole at 79.3°N, 339.8°E, A₉₅ = 5.7° and yielding a paleolatitude of 29.3° ± 5.7°N for the study area. The ChRM directions isolated from the volcanic rocks pass a fold test at 95% confidence, suggesting a primary origin. The volcanic data appear to have effectively averaged out secular variation as indicated by both geological evidence and results from analyzing the virtual geomagnetic pole (VGP) scatter. The mean inclination from the Late Cretaceous red beds, however, is 13.1° shallower than that of the ~ 100 Ma volcanic rocks. After performing an elongation/inclination analysis on 174 samples of the red beds, a mean inclination of 47.9° with 95% confidence limits between 41.9° and 54.3° is obtained, which is consistent with the mean inclination of the volcanic rocks. The site-mean direction of the Late Cretaceous red beds after tilt-correction and inclination shallowing correction is D = 312.6°, I = 47.7°, k = 109.7, α₉₅ = 3.0°, N = 22 sites, corresponding to a paleopole at 49.2°N, 1.9°E, A₉₅ = 3.2° (yielding a paleolatitude of 28.7° ± 3.2°N for the study area). The ChRM of the red beds also passes a fold test at 99% confidence, indicating a primary origin. Comparing the paleolatitude of the Qiangtang terrane with the stable Asia, there is no significant difference between our sampling location in the southern Qiangtang terrane and the stable Asia during ~ 100 Ma and Late Cretaceous. Our results together with the high quality data previously published suggest that an ~ 550 km N–S convergence between the Qiangtang and Lhasa terranes happened after ~ 100 Ma. Comparison of the mean directions with expected directions from the stable Asia indicates that the Gerze area had experienced a significant counterclockwise rotation after ~ 100 Ma, which is most likely caused by the India–Asia collision.