Multi‐Phase Non‐Coaxial Orogenic Growth: Propagation of the Longmen Shan Thrust Belt on the Eastern Margin of the Tibetan Plateau

Abstract

Reconstructing the deformation sequence and strain history of the Longmen Shan thrust belt (LSTB) has significant implications for the growths of the SW Qinling orogenic belt and the Tibetan Plateau. However, the Mesozoic–Cenozoic propagation of the LSTB remains poorly understood owing to weak constraints on strain variations. We conducted a comprehensive structural investigation and made measurements of anisotropy of magnetic susceptibility along the entire LSTB. Magnetic fabrics are represented by prevalent layer‐parallel shortening (LPS) fabrics, intersection lineation fabrics, and folding fabrics with magnetic lineations trending NE–SW, WSW–ENE, NW–SE, and N–S, corresponding to four compressional deformations. AMS results and structural analyses, revealed four phases of deformation (D1, D2, D3, and D4) that were characterized respectively by top‐to‐the‐SSE thrusting in the northern LSTB at >219–164 Ma, top‐to‐the‐SW thrusting in the central‐northern LSTB at >201–164 Ma, top‐to‐the‐SE thrusting of the LSTB at 125–5 Ma, and top‐to‐the‐east thrusting at 5–0 Ma in the LSTB. D1, D3, and D4 LPS fabrics exhibit a strain evolution that progressed from incipient deformation to pencil structure to cleavage fabrics, corresponding to moderately oblate, prolate, and oblate strain ellipsoids, respectively. The intersection lineation fabrics imply a hinterland‐ward progression from LPS fabrics to cleavage‐controlled fabrics and non‐coaxial superimposition of D2 on D1. Therefore, the early Mesozoic LSTB developed owing to the superimposition of D2 on D1 being non‐coaxial, likely suggesting southward growth of the SW Qinling orogenic belt, whereas the modern LSTB was formed by the superimposition of D4 on D3, implying non‐coaxial eastward growth of the Tibetan Plateau.

Fluvial geomorphic parameters of the Shuiluo River Catchment and their tectonic implications, SE Tibetan Plateau

“…Because the rivers are very sensitive to the tectonic uplift at the edge of the Tibetan Plateau, the use of fluvial geomorphology to study neotectonics has become the main direction of the academic community, and then many researches have been carried out (Su et al 2016;Fan et al 2018;Luo et al 2023). The study of the tectonic evolution history around the Tibetan Plateau focuses on its northeast and southeast edges (Chang et al 2015;Chen et al 2018;Gao et al 2019;Sun et al 2022;Wang et al 2022;Zhou et al 2023aZhou et al , 2023bTan et al 2023;Wu et al 2023a, b). Compared with the northeastern edge of the plateau, which is widely used for dating techniques in the Quaternary system, there is relatively limited research on the chronology of eroded bedrock landforms in the southeastern edge, mainly characterized by high mountains and canyons, especially in some typical active tectonic basins (Williams 1987;Zhou et al 2005;Chang et al 2015).…”