Upper Crustal Collapse Reconstructed the Topography and Remodeled the Fault System of the Chuandian Fragment in the Southeastern Edge of the Tibetan Plateau, Evidenced by Anisotropy of Magnetic Susceptibility Data Sets

Abstract

The steps of the southeastward stepwise‐descending topography of the Chuandian Fragment (CDF) in the southeastern edge of the Tibetan Plateau coincide with N‐S and NE‐SW trending faults that changed from thrusting to normal activity, indicating that since the Middle‐Late Miocene the CDF maintained an E‐W oriented extensional tectonic environment. However, the anisotropy of magnetic susceptibility (AMS) data sets presented herein, from the Cretaceous and Cenozoic sedimentary strata of the southeastern Tibetan Plateau and its edge, show that since ∼28.0 Ma the CDF remained within a stabilized compressional stress field, oriented NEE‐SWW. A comprehensive analysis of the AMS results, topography, fault systems, and geophysical observations indicate that the northward‐advancing eastern Himalaya syntaxis impeded the southeastward‐flowing viscous lower crust and correspondingly decreased its flux, which could have reduced the thickness of the lower crustal channel beneath the CDF. The original low‐gradient topography of the CDF formed by the viscous lower crustal flow could no longer be supported by the thinned lower crustal channel, and thus gravity drove the collapse of the uplifted CDF. This process reconstructed the topography and remodeled the preexisting fault systems of the CDF, resulting in the coexistence of the E‐W oriented extensional tectonic environment and the stabilized NEE‐SWW oriented compressional stress field of the western part of the CDF, since the Middle‐Late Miocene. Thus, the change in the status of the lower crustal channel related to block interactions provided a major geodynamic setting for shaping the topography of the southeastern edge of the Tibetan Plateau.

Paleomagnetic studies of Jurassic and Cretaceous rocks in the Eastern Qiangtang Terrane, Tibetan Plateau, China

“…the collision between the Qiangtang and the northern terranes, such as the Songpan-Ganzi Terrane and Tarim Basin (e.g., Kapp et al, 2003b;Pan et al, 2004a;Pullen et al, 2008;Li et al, 2009a;Gehrels et al, 2011;Zhu et al, 2013;Song et al, 2015Song et al, , 2017Song et al, , 2020Yu et al, 2022a), the closure of the Meso-Tethys-Bangong-Nujiang Ocean, i.e. the Lhasa Qiangtang collision ( e.g., Metcalfe et al, 2006;Zhu et al, 2011;Zhang et al, 2012;Ding et al, 2013;Fan et al, 2014;Yan et al, 2016;Chen et al, 2017bChen et al, , 2020, and the crustal shortening and widespread lateral extrusion of lithospheric blocks after the 10|Page India-Eurasia collision (e.g., Tapponnier et al, 1982;Otofuji et al, 1990;Huang et al, 1992;Tong et al, 2015Tong et al, , 2017Tong et al, , 2022Li et al, 2020b;Zhang et al, 2020a). Van Hinsbergen et al (2012).…”

“…In the north of the EHS, at least in the Qamdo region (Nangqian, Gongjue and Mangkang areas) and the Zaduo area, it is the northward compression rather than rotation that dominated the far field effect of India-Eurasia collision before the late Eocene (Xu et al, submitted). Afterwards, widespread clockwise rotation of the southeast Tibetan Plateau occurred after the late Eocene (e.g., Tong et al, 2017Tong et al, , 2022Zhang et al, 2020a;Li et al, 2020b;2020c;Todrani et al, 2022;Xu et al, submitted;Fig. 4.11C).…”

“…Geodetic observations provided constraints on the present-day clockwise rotation of the eastern Tibetan Plateau (Shen et al, 2005;Wang & Shen, 2020;Wang et al, 2021). Evidence from paleomagnetism revealed the clockwise rotation and lateral extrusion since the Cenozoic (Yang et al, 2001b;Kondo et al, 2012;Tong et al, 2017Tong et al, , 2022. Geophysical investigations reported on various features of the region including lowvelocity and high-conductivity zones with high Poisson's ratios (Wang et al, 2007;Bai et al, 2010;Liu et al, 2014b;Bao et al, 2015).…”