Formation Of Tibetan Plateau Research Articles

Elevation of the Gangdese Mountains and Their Impacts on Asian Climate During the Late Cretaceous—a Modeling Study

Uplift of the Gangdese Mountains is important to the evolution of Asian monsoons and the formation of Tibetan Plateau, but its paleoaltitude before the India-Asia collision (Late Cretaceous) is less constrained so far. In this study, we investigate whether the geological records, which are indicators of soil dryness, discovered in East Asia can provide such a constraint. Through climate modeling using the Community Earth System Model version 1.2.2, it is found that the extent of dry land in East Asia is sensitive to the altitude of the Gangdese Mountains. It expands eastwards and southwards with the rise of the mountain range. Comparison of the model results with all the available geological records in this region suggests that the Gangdese Mountains had attained a height of ∼2 km in the Late Cretaceous.

The Cretaceous crustal shortening and thickening of the South Qiangtang Terrane and implications for proto-Tibetan Plateau formation

The timing and magnitude of deformation across the central Tibetan Plateau, including the South Qiangtang Terrane (SQT), are poorly constrained but feature prominently in geodynamic models of the Tibetan Plateau formation. The Ejiu fold and thrust belt (EFTB), which is located in the SQT, provides valuable records of the Mesozoic-Cenozoic deformation history of the central Tibetan Plateau. Here we integrate geochronology of volcanic rocks, low-temperature thermochronology, geologic mapping and a balanced cross section to resolve the deformation history of the SQT. Geochronologic data suggest that major deformation that initiated in the early Cretaceous continued until at least 80 Ma and ceased by ∼40 Ma. The balanced cross section resolves ∼66 km upper crustal shortening (34%) mainly during the Cretaceous Qiangtang-Lhasa collision. However, the Cenozoic crustal shortening is not well constrained because of a lack of successive Cenozoic strata. We also discussed whether the observed crustal shortening can account for the modern crustal thickness and elevation in the SQT. Our observations indicate that crustal shortening and thickening within the central Tibetan Plateau was mostly accomplished during the Cretaceous Lhasa-Qiangtang collision. A thick crust could be maintained since the Cretaceous due to slow erosion rates since ∼40 Ma. Minor Late Cenozoic shortening also contributed to a small amount of crustal thickening in the central Tibetan Plateau. However, close to modern >4700 m elevation was finally attained by lithospheric mantle foundering in the Qiangtang Terrane at ∼25 Ma.

Crustal rheology controls on the Tibetan plateau formation during India-Asia convergence

The formation of the Tibetan plateau during the India-Asia collision remains an outstanding issue. Proposed models mostly focus on the different styles of Tibetan crustal deformation, yet these do not readily explain the observed variation of deformation and deep structures along the collisional zone. Here we use three-dimensional numerical models to evaluate the effects of crustal rheology on the formation of the Himalayan-Tibetan orogenic system. During convergence, a weaker Asian crust allows strain far north within the upper plate, where a wide continental plateau forms behind the orogeny. In contrast, a stronger Asian crust suppresses the plateau formation, while the orogeny accommodates most of the shortening. The stronger Asian lithosphere is also forced beneath the Indian lithosphere, forming a reversed-polarity underthrusting. Our results demonstrate that the observed variations in lithosphere deformation and structures along the India-Asia collision zone are primarily controlled by the strength heterogeneity of the Asian continental crust.

Three-dimensional structural model of the Qaidam basin: Implications for crustal shortening and growth of the northeast Tibet

AbstractThe Qaidam basin, bounded by the Altyn Tagh fault in the north, is located in the northeast of the Tibet plateau, and it has important implications for understanding the history and mechanism of Tibetan plateau formation during the Cenozoic Indo-Eurasia collision. In this study, we constructed the main geological structures and surfaces in three dimensions through the interpolation of regularly spaced 2D seismic sections, constrained by wells data and surface geology of the Qaidam basin in northeast Tibet. Meanwhile the Cenozoic tectonic history of the Qaidam basin was reconstructed and the uplift mechanism of the Tibetan plateau was discussed. This study presents the subsurface data in conjunction with observations and analysis of the stratigraphic and sedimentary evolution. The Cenozoic deformation history of the Qaidam basin shows geologic synchroneity with uplifting history of the Tibet Plateau. It is therefore proposed that the deformation and uplifting in the south and north edges of the Tibet Plateau was almost synchronous. The total shortening and shortening rate during Cenozoic reached 25.5 km and 11.2% respectively across the Qaidam basin, indicating that the loss of the left-lateral strike slip rates of the Altyn Tagh fault has been structurally transformed into local crustal thickening across NW-trending folds and thrust faults. Meanwhile there is an about 11° vertical component along the strike-slip Altyn Tagh fault, the block oblique slip shows one more growth mechanism of the northeast Tibet.

Testing models of Tibetan Plateau formation with Cenozoic shortening estimates across the Qilian Shan–Nan Shan thrust belt

Competing models that account for the construction of the Tibetan Plateau include continental subduction, underthrusting, distributed shortening, channel flow, and older crustal-structure inheritance. Well-constrained estimates of crustal shortening strain serve as a diagnostic test of these plateau formation models and are critical to elucidate the dominant mechanism of plateau development. In this work we estimate the magnitude of Cenozoic shortening across the northern Qilian Shan–Nan Shan thrust belt, along the northeastern plateau margin, based on detailed analysis and reconstruction of three high-resolution seismic reflection profiles. By integrating surface geology, seismic data, and the regional tectonic history, we demonstrate that this thrust system has accumulated >53% Cenozoic strain (∼50 km shortening), accommodated by several south-dipping thrust faults. Based on the observed strain distribution across northern Tibet, including lower strain (30%–45%) within the interior of the Qilian Shan–Nan Shan thrust belt, we suggest that a combination of distributed crustal shortening and minor (

Crustal structure and Moho geometry of the northeastern Tibetan plateau as revealed by SinoProbe-02 deep seismic-reflection profiling

Underthrusting of India below Eurasia has resulted in the formation of the Himalayan and the Qinghai–Tibet Plateau. Distributed deformation coupled with block translation and rotation has generated the Qilian Shan thrust belt and a series of east- and northwest-striking strike-slip faults across northeastern Tibet. Because these structures lie in a transition zone between the high plateau region to the south and the lowlands of the North China craton in the north, determining their deep-crustal and upper-mantle structures has important implications for unraveling the mechanism of Tibetan plateau formation. In this paper, we present new results from the SinoProbe-02 deep seismic reflection project across the eastern part of the Qilian Shan and the southern margin of the Alxa block. Interpretation of the reflection profile obtained from this study is based on constraints from surface geology and detailed geometric analysis of structural relationships among key reflectors in the crust and the upper mantle. Our results indicate that the upper crust of the eastern Qilian Shan is characterized by fault-bend folds and duplex systems involving Phanerozoic strata that may have resulted from early Paleozoic collisional tectonics and Cenozoic intra-continental deformation. Locally, half-graben structures hosting Cretaceous strata are also present. The active structures in the region are dominated by left-slip Haiyuan and Tianjian fault systems marking the northern margin of the Tibetan plateau. The strike-slip structures have variable dips and dip directions and sole into a common décollement with a depth of 40–45km. Because the two faults do not cut and offset the Moho below, the active crustal and mantle deformation in the northeastern Tibet must be decoupled.

Cenozoic tectonic evolution of Qaidam basin and its surrounding regions (Part 1): The southern Qilian Shan-Nan Shan thrust belt and northern Qaidam basin

Cenozoic Qaidam basin, the largest active intermountain basin inside Tibet, figures importantly in the debates on the history and mechanism of Tibetan plateau formation during the Cenozoic Indo-Asian collision. To determine when and how the basin was developed, we conducted detailed geologic mapping and analyses of a dense network of seismic reflection profiles from the southern Qilian Shan-Nan Shan thrust belt and northern Qaidam basin. Our geologic observations provide new constraints on the timing and magnitude of Cenozoic crustal thickening in northern Tibet. Specifically, our work shows that the southernmost part of the Qilian Shan-Nan Shan thrust belt and contractional structures along the northern margin of Qaidam basin were initiated in the Paleocene-early Eocene (65–50 Ma), during or immediately after the onset of the Indo-Asian collision. This finding implies that stress was transferred rapidly through Tibetan lithosphere to northern Tibet from the Indo-Asian convergent front located >1000 km to the south. The development of the thrust system in northern Qaidam basin was driven by motion on the Altyn Tagh fault, as indicated by its eastward propagation away from the Altyn Tagh fault. The eastward lengthening of the thrust system was spatially and temporally associated with eastward expansion of Qaidam basin, suggesting thrust loading was the main control on the basin formation and evolution. The dominant structure in northern Qaidam basin is a southwest-tapering triangle zone, which started to develop since the Paleocene and early Eocene (65–50 Ma) and was associated with deposition of an overlying southwest-thickening, growth-strata sequence. Recognition of the triangle zone and its longevity in northern Qaidam basin explains a long puzzling observation that Cenozoic depocenters have been located consistently along the central axis of the basin. This basin configuration is opposite to the prediction of classic foreland-basin models that require the thickest part of foreland sediments deposited along basin edges against basin-bounding thrusts. Restoration of balanced cross sections across the southern Qilian Shan-Nan Shan thrust belt and northern Qaidam basin suggests that Cenozoic shortening strain is highly inhomogeneous, varying from ~20% to >60%, both vertically in a single section and from section to section across the thrust belt. The spatially variable strain helps explain the conflicting paleomagnetic results indicating different amounts of Cenozoic rotations in different parts of Qaidam basin. The observed crustal shortening strain also implies that no lower-crustal injection or thermal events in the mantle are needed to explain the current elevation (~3000–3500 m) and crustal thickness (45–50 km) of northern Qaidam basin and the southern Qilian Shan-Nan Shan thrust belt. Instead, thrusting involving continental crystalline basement has been the main mechanism of plateau construction across northern Qaidam basin and the southern Qilian Shan-Nan Shan region.

Did the Altyn Tagh fault extend beyond the Tibetan Plateau?

The pre-Miocene northeastern termination of Altyn Tagh fault is a critical outstanding problem for understanding the mechanics of Cenozoic deformation resultant from the Indo-Asian collision and mechanisms of Tibetan Plateau formation. Structures beyond the widely accepted NE end of the Altyn Tagh fault, near the town of Yumen, are needed in order to accommodate strike-slip deformation related to plate-like lateral extrusion tectonics, but structures with the necessary slip magnitudes and histories have not been identified. We report on a series of newly recognized and documented E to ENE-striking faults within the Alxa block, NE of the Tibetan Plateau, that are visible on remotely sensed images and confirmed by field studies. These structures are demonstrably left-lateral faults based on offset geology and kinematic indicators such as striae and s–c fabrics in fault gouge. The faults have post-Cretaceous offsets of at least tens to possibly > 150 km, but limited post-Miocene displacement, constrained by offset sedimentary basins. These characteristics suggest that strike-slip faults of the Alxa region have a similar structural history as the central-eastern Altyn Tagh fault and can provide a mechanism for accommodating Oligocene–Early Miocene extrusion along the Altyn Tagh fault.

Preliminary paleomagnetic study of Cretaceous dykes in SE-Tibet

DOI = 10.3126/hjs.v5i7.1231 Himalayan Journal of Sciences Vol.5(7) (Special Issue) 2008 p.20

Formation of Tibetan Plateau Considered from the Wandering of the Pole

Formation of Tibetan Plateau Considered from the Wandering of the Pole