Block rotation: Tectonic response of the Sichuan basin to the southeastward growth of the Tibetan Plateau along the Xianshuihe‐Xiaojiang fault

Abstract

GPS field and seismic data show that the southeastern margin of the Tibetan Plateau is tectonically and seismically active. This activity is due to the southeastward extrusion of the Chuandian fragment, a large crustal block rotating clockwise around the northeastern syntaxis of the Himalayas. The eastern boundary fault of this fragment is defined by the left-lateral Xianshuihe-Xiaojiang fault, which abruptly truncates the Sichuan basin of the Yangtze block. Our paper presents evidence indicating that the Sichuan basin experienced right-lateral shear along its margin, including the Longmen Shan fault belt, as shown by the presence of a large number of interference deformation features, including S-shaped and Z-shaped folds and faults, aligned in an en echelon pattern. This study hypothesizes that the Sichuan basin experienced counterclockwise rotation, dragged by the left-lateral movement along the Xianshuihe fault, and it is this rotation that was the underlying cause of the 12 May 2008 Wenchuan M s 7.9 earthquake. During the rotation, the Sichuan basin decoupled along a subhorizontal decollement fault zone that developed along Triassic gypsum-and coal-bearing rocks, at a mean depth of~5000 m, below which the Paleozoic rocks experienced much more intense deformation than the overlying Mesozoic rocks, suggesting that the lower part of the basin experienced a larger-scale rotation relative to the uppermost part of the basin. Based on thermal data from the western margin of the Sichuan basin and from along the Xianshuihe fault, the counterclockwise bending/rotation of the Sichuan basin initiated in late Cenozoic time (~13 Ma).

Tectonic uplift of the Xichang Basin (SETibetan Plateau) revealed by structural geology and thermochronology data

“…Collectively, most of the studies suggest a marked acceleration in cooling and exhumation from rates of ca. Burchfiel et al, 1995;Liu et al, 2012;Wang et al, 2014). 40-10 Ma.…”

“…to form the western Sichuan foreland basin Li et al, 2003). Chen et al, 1995;Burchfiel et al, 1995;Wang et al, 2014). 1).…”

“…rectangles and ellipses along boundary faults represent the correlation between cooling age measured in the Xichang Basin and cooling ages across the continental collision zone in eastern Tibet. Wang et al, 1998Wang et al, , 2014Roger et al, 2010). (b) Swath profile across eastern Tibet to the Sichuan Basin, indicating significant difference in elevation across the region and an uplifted Xichang Basin in comparison with the Sichuan Basin.…”

New paleomagnetic constraints on middle Miocene strike‐slip faulting along the middle Altyn Tagh Fault

“…A growing body of evidence indicates the partitioning of oblique motion into boundary‐parallel strike‐slip motion, orthogonal thrusting, and vertical axis rotation for the Cenozoic deformation of the Tibetan Plateau [ Avouac and Tapponnier , ; Meyer et al ., ]. In particular, vertical axis rotation of crustal blocks is a ubiquitous feature of continental deformation [ McKenzie and Jackson , ; Chen et al ., ; Zhang et al ., ], and it is a characteristic of regions near transpressional strike‐slip faults, such as the ATF [ Chen et al ., ; Lu et al ., ; Wang et al ., , ], the Ailaoshan‐Red River Fault, and the Xianshuihe‐Xiaojiang Fault [ Wang et al ., ]. Measurements of paleomagnetic declination can reveal past vertical axis rotations of geological bodies, since they become magnetized, and this independent method can shed new light on the evolution of the ATF.…”

GPS Strain Rate and Seismic Activity Before the Ludian Earthquake (Ms 6.5), Northeast Yunnan, China: New Implications for Eastward Chuan-Dian Block Extrusion

“…However, the dynamic accommodation for the eastward sub-motion remains controversial. One argument speculates that the differential clockwise rotation produced by Sichuan basin counterclockwise rotation dragging should play an important role (Xu et al 2003;Shen et al 2005;Wang et al 2014). The second hypothesis considers that the eastward expansion may simply be explained by vertical crustal shortening deformation (He and Ikeda 2007;Chen and He 2008;Wen et al 2011Wen et al , 2013.…”