Search

The timing of the development of the highland topography along the northern margin of the Tibetan Plateau is the key to understanding the manner of Tibetan growth and the far-field effects of the collision between India and Eurasia. Although various studies have investigated the exhumation and uplift of the basement rocks, thermochronological studies on the detritus from a continuous depositional sequence inan intermontane basin are lacking but might shed light on this issue. In this study, a set of detrital apatites from an upper Eocene to Pliocene depositional sequence in the Kumukol Basin, the largest intermontane basin in the East Kunlun, were dated by using the (U-Th)/He technique. The detrital apatites had consistent ages of ∼40 Ma for all deposit formations from bottom to top, which were older than the depositional ages. The ages and their consistency suggested that these detrital apatites were not reset and that the ages represented the original ages in the provenance region. These detrital apatite ages from the upper Eocene to Pliocene formations strongly suggested that the high mountains surrounding the Kumukol Basin formed at or before ∼40 Ma and have remained high since then. The process of mountain building resulted in a prolonged period of erosion from ∼40 to 2.6 Ma. The coupling of mountain and basin at ∼40 Ma was widespread along the East Kunlun. Our present results constrain the time of onset of the mountain building along the northern margin of the Tibetan Plateau, which may represent a rapid response to the India-Eurasian collision. [ABSTRACT FROM AUTHOR]

How does the rising Tibetan Plateau affect its peripheral region? The current understanding of the mechanism of orogenic plateau development is incomplete and thus no consensus yet exists in this regard. However, our new 40 Ar/ 39 Ar and (U–Th)/He dataset presented in this study may shed some light on this issue. 40 Ar/ 39 Ar dating, on two vertical transects from the massif between Nuomuhong and Golmud, indicates that the Eastern Kunlun Range was built-up and exhumated during the later Triassic initially, and a minimum overburden of ~ 11.7–14.0 km has been eroded since ~ 220 Ma. (U–Th)/He age–elevation relationships (AERs) indicate a rapid exhumation event at ~ 40 Ma following a long period of slow exhumation phase from late Mesozoic to early Eocene time. In this study, two scenarios – one assuming a single stage and the other assuming multiple stages of evolution history – are modeled. Modeling of a multiple stage scenario is reasonable and is able to reflect the “actual” situation, which reveals the entire denudation and relief history of the northern Tibet from late Mesozoic to the present time. After prolonged denudation before 50 Ma, a low topography (~ 0.17 times the relief of the present) developed by 50 Ma with an erosion rate of 0.013 -0.013 + 0.025 mm/yr. The highest relief (~ 1.82 times the relief of the present) of the Cenozoic time came into being at 40 Ma with an erosion rate of 0.052 ± 0.025 mm/yr, which was possibly a result of the collision between India and Eurasia. Subsequently, the relief steadily decreased to the present level due to continued denudation. This suggests that deformation propagation from the continued convergence boundary between India and Eurasia was insignificant after the construction of the highest relief. This observation is broadly consistent with published accounts on the stratigraphic, cooling, and faulting histories of the northern Tibet margin. [ABSTRACT FROM AUTHOR]

Abstract: Models to explain the distributed nature of continental deformation predict the propagation of strain and high topography away from the plate boundary. Yet a growing body of evidence in the Tibetan orogen suggests that deformation occurred at the far northern extent of the modern plateau early in the orogen''s history and thus our current mechanical understanding of orogenic plateau development is incomplete. New apatite (U–Th)/He ages from four elevation transects document periods of rapid exhumation related to erosion pulses in hanging wall rocks of major thrust structures. Accelerated erosion is used as a proxy of fault timing, and is interpreted in a larger context of structural data and sediment accumulation in adjacent foreland basins. Helium results are synthesized with published geologic, thermochronometric, and sedimentologic data from which a growing picture of regional compressional deformation in Middle to Late Eocene time in northern Tibet emerges. We relate the early Cenozoic period of deformation to the initiation of collision between India and Eurasia, despite the fact that the plate boundary was located >3000km to the south. Regardless of whether or not high topography was built simultaneously as a result of this deformation, early Cenozoic strain signifies that the modern limit of the orogen has been relatively stationary since continental collision began and that deformation has not significantly propagated farther away from the plate boundary in time. [Copyright &y& Elsevier]