The Cenozoic growth of the Qilian Shan in the northeastern Tibetan Plateau: A sedimentary archive from the Jiuxi Basin

Abstract

Sedimentary deposits in Tibetan Basins archive the spatial‐temporal patterns of the deformation and surface uplift processes that created the area's high topography during the Cenozoic India‐Asia collision. In this study, new stratigraphic investigation of the Caogou section from the Jiuxi Basin in the northeasternmost part of Tibetan Plateau provides chronologic constraints on the deformation and northward growth of the plateau. Magnetostratigraphic analysis results suggest that the age of the studied ~1000 m thick section spans from ~24.2 Ma to 2.8 Ma. Detailed sedimentology and apatite fission track (AFT) analyses reveal that variations in the clast provenance, lithofacies, sediment accumulation rates, and AFT lag times occurred at ~13.5–10.5 Ma. We interpret these changes as in response to the initial uplift of the North Qilian Shan. In addition, paleomagnetic declination results from the section indicate a clockwise rotation of the Jiuxi Basin before ~13.5 Ma, which was followed by a subsequent counterclockwise rotation during 13.5–9 Ma. This reversal in rotation direction may be directly related to left‐lateral strike‐slip activity along the easternmost segment of the Altyn Tagh Fault. Combined with previous studies, we suggest that movement on the western part of the Altyn Tagh Fault was probably initiated during the Oligocene (>30 Ma) and that fault propagation to its eastern tip occurred during the middle‐late Miocene.

Expansion of the Tibetan Plateau during the Neogene

“…These changes are interpreted to reflect the onset of rapid uplift of the Qilian Shan during the late Miocene. Notably, a similar shift in sediment provenance is observed along the northern margin of the Qilian Shan, in the Hexi Corridor at ca.12 Myr50 and thermochronology from the northern portion of the range suggest that onset of rapid exhumation occurred at ca. 10 Myr ago51.…”

Miocene Range Growth Along the Altyn Tagh Fault: Insights From Apatite Fission Track and (U‐Th)/He Thermochronometry in the Western Danghenan Shan, China

“…By analyzing provenance of conglomerate in the NW Qaidam Basin, Wu, Xiao, Yang, et al () also proposed a two‐stage evolution model for the Altyn Tagh fault: (1) Altyn Tagh fault was a basal shear zone confined in the middle‐lower crust during the first stage of ~36–15 Ma; (2) crust beneath the Altyn Mountain was split and left‐slip movement initiated at ~15 Ma. Based on magnetostratigraphic analysis results in the western Hexi Corridor and previous studies, W. Wang, Zhang, Pang, et al () proposed a two‐stage northward propagated model of the Altyn Tagh fault, in which the fault terminated in the western Qaidam Basin in Eocene–Oligocene, then it propagated to the northeast to its present eastern end by ~13 Ma. In this model, the intensive crustal shortening and rapid growth of the Qilian Shan has initiated since the middle Miocene.…”

Constraints on mountain building in the northeastern Tibet: Detrital zircon records from synorogenic deposits in the Yumen Basin

“…They suggest that the previous fast strike-slip movement along the ATF in northeast Tibet slowed down abruptly in the mid-Miocene, and renewed reverse faulting within the Qilian Shan region transferred the fault slip from the AFT to shortening and range growth. However, numerous studies have yielded evidence for emergence of the Qilian Shan occurring almost simultaneously along its southern to northern parts at 16–10 Ma, such as magnetostratigraphic dating of sediments to derive sediment accumulation rates or provenance changes in the Qaidam Basin33, Subei Basin2627, Hexi Corridor Basin1728; and low-temperature thermochronology dating of detrital minerals to define rapid exhumation of the adjacent ranges1125 (Fig. 3).…”

“…The age of these stratigraphic units is based on fossils of mammalian, ostracode, and palynological assemblages and magnetostratigraphy817.…”

“…1B). This section, known as the Caogou section, was dated using high-resolution magnetostratigraphic dating and was deposited between ~24.2 Ma and ~2.8 Ma17. Six fine- to coarse-grained sandstone samples were collected from the section and from sediments dated to 23.8 Ma, 20.6 Ma, 16.7 Ma, 15.8 Ma, 13.2 Ma and 7.5 Ma (Supplementary Fig.…”