Jurassic-Early Cenozoic Tectonic Inversion in the Qilian Shan and Qaidam Basin, North Tibet: New Insight From Seismic Reflection, Isopach Mapping and Drill Core Data

Abstract

The pre-Cenozoic structural pattern of Asia has had a strong impact on the localization and propagation of the Cenozoic deformation that gave birth to the Tibetan Plateau. Northern Tibet represents a key area to decipher the structural and kinematic links between the Mesozoic and Cenozoic evolution of Tibet. Nonetheless, the Mesozoic tectonic setting of the North Tibet and the role that the Paleozoic inherited Altyn Tagh Fault (ATF) shearing zone played in controlling the regional tectonic pattern during the deposition of the Mesozoic strata remain controversial. This study is based on seismic reflections, isopach maps of the Mesozoic strata in the Qaidam Basin, and provenance analysis using detrital zircon geochronological and heavy mineral contents. Seismic reflections and isopach maps demonstrate that sustained strike-slip motion along the ATF during the Early to Late Jurassic induced transtensional basin formation. Further away from the main ATF (eastern parts of the Qilian Shan and the northern Qaidam Basin), transtension also occurred along major faults, although local transpression developed in relay zones. Rotation in the regional stress field induced compression and basin inversion during the Late Jurassic to Early Cretaceous. The Cenozoic sedimentary rocks in these regions display widespread growth strata and angular unconformities characteristic of compression. This is consistent with topographic changes marked by sediment source variation evidenced by detrital zircon geochronology and heavy mineral analysis. We propose that the mechanism driving the Jurassic extension/transtension in North Tibet could be related to far-field effects of subduction processes along the southern margins of the continent.

Diachronous Growth of the Northern Tibetan Plateau Derived From Flexural Modeling

“…In particular, it is usually assumed that the Eastern Kunlun Shan to the south was higher than the Qilian Shan during the Paleogene (Tapponnier et al., 2001; Wang et al., 2008; W Wang et al., 2017). Some studies have indicated, however, that pre‐Cenozoic topography might have existed in Northern Tibet, suggesting that the Paleogene paleoelevation of the northern Tibetan plateau could be partly inherited from pre‐existing topographic relief (Cheng, Fu, et al., 2016; Cheng, C. N. Garzione, Jolivet, et al., 2019; Cheng, Jolivet, et al., 2019; Jolivet et al., 2001; Robinson et al., 2003). All these deductions are based on the indirect knowledge of the deformation history of the mountain belts and source to sink analysis.…”

Contributions of Triassic Tectonism to Build the Northern Tibetan Plateau: Insights From Tectonic Evolution of the Jinhongshan Range, Central Altyn Tagh Fault System

“…Similar Middle Jurassic extensional event has been inferred from surface normal‐sense shear zones in the eastern Altyn Tagh range (Chen, Yin, et al, 2003) (Figure 10b). These extensional records demonstrate that at least the Qaidam and eastern Altyn Tagh domains of North Tibet evolved into an extensional setting during Early‐Middle Jurassic time (e.g., Cheng et al, 2019; Zuza et al, 2018). The driving force for extension was variously interpreted, as being attributed to either far‐field effects of subduction processes along the southern edge of Eurasia (Cheng et al, 2019; Morin et al, 2018), or postcollisional extension following the closure of the Paleo‐Tethys Ocean and the docking of the Qiangtang block (Yu et al, 2017).…”

“…Notably, recent seismic profiling of the Qaidam basin reveals evidence of Early‐Middle Jurassic growth strata bounded by normal faults (Cheng et al, 2019). This finding, in agreement with results of provenance and facies analysis of sediments (Yu et al, 2017), implies Early‐Middle Jurassic extension within the Qaidam basin (Figure 10b), which possibly corresponds to pull‐apart basin opening or transtensional relay zone generation, in response to sinistral slip along the ATF zone (Cheng et al, 2019). Similar Middle Jurassic extensional event has been inferred from surface normal‐sense shear zones in the eastern Altyn Tagh range (Chen, Yin, et al, 2003) (Figure 10b).…”

“…Due to intense overprinting by Cretaceous to Cenozoic tectonism (e.g., Yin, 2010), the Jurassic tectonic framework of North Tibet remains poorly understood. Notably, recent seismic profiling of the Qaidam basin reveals evidence of Early‐Middle Jurassic growth strata bounded by normal faults (Cheng et al, 2019). This finding, in agreement with results of provenance and facies analysis of sediments (Yu et al, 2017), implies Early‐Middle Jurassic extension within the Qaidam basin (Figure 10b), which possibly corresponds to pull‐apart basin opening or transtensional relay zone generation, in response to sinistral slip along the ATF zone (Cheng et al, 2019).…”

Topographic growth of the northeastern Tibetan Plateau during the middle‐late Miocene: Insights from integrated provenance analysis in the NE Qaidam Basin

“…Low‐temperature thermochronologic data reveal accelerated exhumation related to thrust faulting around the middle Miocene (Lease et al., 2011; Meng et al., 2020; Pang et al., 2019; Wang, Zheng, et al., 2020; Yu, Pang, et al., 2019; Yu, Zheng, et al., 2019; Zheng et al., 2010; Zhuang et al., 2018). However, debates still exist as to the mechanisms of the Cenozoic deformation in the entire Qilian Shan (Meyer et al., 1998; Zuza et al., 2016, 2019), relationship(s) between pre‐Cenozoic structures and Cenozoic deformation (Chen, Shao, et al., 2019; Cheng, Jolivet, et al., 2019), whether the entire Qilian Shan has experienced multi‐phased uplift (Li, Zuza, et al., 2020; Qi et al., 2016; Zhuang et al., 2011) or synchronous uplift (Yu, Zheng, et al., 2019), and whether the Qilian Shan has undergone a gradual northward propagation (Bovet et al., 2009; Cheng, Garzione, Jolivet, et al., 2019) or outward expansion in opposite directions in the Cenozoic (Pang et al., 2019). These uncertainties limit our understanding of how the Tibetan Plateau has grown and underlying geodynamic processes.…”