Early Cretaceous contractional deformation and structural evolution of Northeastern Tibetan Plateau, northwestern China: Constraining the initial condition of Cenozoic construction of the plateau

Abstract:

It is always argued that the Tibetan Plateau was created by the Indo-Asian collision alone, or together with the effect of the Cretaceous Lhasa-Qiangtang collision. The north margin of the Qilian Shan is the most front of the uplift and northeastward expanding of the Tibetan Plateau. To examine this argument, we conducted field geological mapping and detrital zircon U-Pb dating of a Cretaceous basin in northern margin of the Qilian Shan. Structural analyses reveal multiple-phase deformations since Early Cretaceous, including the first-phase of NE-directed contractional folding in the earlier Early Cretaceous and the second-phase of extensional normal faulting in the later Early Cretaceous. The third-phase produced NW-trending dextral strike-slip faulting and duplexing in the later Early Cretaceous and followed by the fourth-phase of relatively gentle NE-directed folding since late Miocene. This implies large amount of Cretaceous crustal shortening (~42%) and thickening in the region. We suggest that this was the far-field response of the collision between the Lhasa and the Qiangtang terranes in the south during Early Cretaceous. Our LA MC-ICP-MS U-Pb dating of Lower Cretaceous detrital zircons, indicates source derivation both from the Alxa Terrane in the north and the North Qilian Shan in the south, implying both high elevations of them in Early Cretaceous. The sink source of the Miocene strata in the region might dominantly come from the Alxa Terrane in the north, implying not high elevation of the North Qilian Shan in the south. We conclude that the northeastern Tibetan Plateau experienced crustal shortening and thickening in Early Cretaceous, denudation and planation in Late Cretaceous and Paleogene, and forming its high-elevation due to folding and thrusting since Miocene.