Late Cenozoic east–west crustal shortening in southern Longmen Shan, eastern Tibet: Implications for regional stress field changes Zhigang Li a , Dong Jia a, ⁎, Wei Chen b , Hongwei Yin a , Li Shen a , Chuang Sun a , Yong Zhang a , Yiquan Li a , Shiqin Li b , Xiaojun Zhou b , Haibin Li a , Gaoming Jian c , Meng Zhang a , Jian Cui a a Department of Earth Sciences and Institute of Energy Sciences, Nanjing University, Nanjing 210093, China b Resources and Environment Institute, Southwest Petroleum University, Chengdu 610500, China c The Southwest Branch of SINOPEC, Chengdu 610016, China abstract article info Article history: Received 16 April 2013 Received in revised form 4 March 2014 Accepted 28 March 2014 Available online 18 April 2014 Keywords: Wenchuan earthquake Crustal shortening Longmen Shan Fault slip rate Stress field changes The co-seismic slip sense of the 2008 Wenchuan earthquake (Mw 7.9) has resulted in the present east–west (E–W) crustal shortening and oblique thrusting across Longmen Shan, which are inconsistent with southeast-directed thrusting that occurred during the late Triassic. Although the two major periods of compres- sional deformations in Longmen Shan have long been recognized, the fault slip rate of the late Cenozoic deforma- tion and the initial E–W crustal shortening remain poorly investigated. This study confirms the fault slip rate in the Dayi Thrust Fault System (DYFS) based on data from the petroleum industry and shallow seismic reflection profiles, and well data. Folded late Pliocene to present strata are analyzed and yield with an average slip rate of 0.2 mm/yr on the DYFS. An average fault slip rate of 0.25 mm/yr is then obtained from the late Pliocene to present for the range front thrust of Longmen Shan. The E–W crustal shortening is investigated by using 3-D seis- mic reflection data, interpreting satellite image, and conducting a field investigation in the DYFS to determine stress field changes during the late Cenozoic. Two-period tectonic deformations during the late Cenozoic are found in the DYFS, which correspond to the NE- and NS-trending structures, respectively. The activities of the DYFS may reflect a change in the field direction of the regional stress—from NW–SE during the Oligocene to early Pliocene to E–W during the late Pliocene to Holocene, which is consistent with the present stress measure- ments. The 120 km NS-trending structures in the southern Longmen Shan range front as well as the Wenchuan earthquake co-seismic ruptures are assumed to reflect the active, E–W crustal shortening in Longmen Shan. © 2014 Elsevier B.V. All rights reserved. 1. Introduction The devastating Mw 7.9 Wenchuan earthquake in Longmen Shan on May 12, 2008 resulted in enormous economic losses and casualties by destroying the homes of more than 1.5 million people (Stone, 2008). The earthquake also resulted in crustal shortening along the eastern margin of the Tibetan Plateau (Hubbard and Shaw, 2009; Liu-Zeng et al., 2009; Wang et al., 2011; Zhao et al., 2012). Field investigations show that the co-seismic surface slip of the Wenchuan earthquake along the NE-trending Longmen Shan is mainly divided into the oblique right-lateral reverse faulting on the NW-dipping Yinxiu–Beichuan Fault (~260 km long), the nearly pure thrusting on the NW-dipping Pengguan Fault (~ 70 km long), the oblique reverse right-lateral faulting on the NW-dipping Qingchuan Fault (~60 km long), and the oblique reverse left-lateral faulting on the SW-dipping Xiaoyudong Fault (~8 km long) (Jia et al., 2010; Li et al., 2010; Lin et al., 2012; Liu-Zeng et al., 2009, 2012; Wang et al., 2011; Xu et al., 2009; Zhang et al., 2010)(Fig. 1). This slip sense highlights present east–west (E–W) crustal shortening and oblique thrusting across Longmen Shan, which has not been entirely validated in previous studies (Liu-Zeng et al., 2009; Luna and Hetland, 2013). This crustal shortening implies a change in the direc- tion of the stress field. According to Burchfiel et al. (1995), Longmen Shan has been formed by southeast-directed thrusting during the late Triassic, which has been accommodated by NE-trending structures. Although the compressional deformations during the late Triassic and the Cenozoic as well as the related folds and blind thrusts in Longmen Shan have long been recognized and mapped, the initial E–W crustal shortening remains unclear (Burchfiel et al., 1995; Chen and Wilson, 1996; Jia et al., 2006). Moreover, the Quaternary slip rate of the Dayi Thrust Fault System (DYFS) and the range front thrust of Longmen Shan are poorly investigat- ed compared with that of other faults in Longmen Shan and the Sichuan Basin, such as Yinxiu–Beichuan, Pengguang, and Qiongxi (Arne et al., 1997; Densmore et al., 2007; Godard et al., 2009; Kirby et al., 2002; Wang et al., 2013b). Tectonophysics 623 (2014) 169–186 ⁎ Corresponding author at: Institute of Energy Sciences, Department of Earth Sciences, Nanjing University, Hankou Road No. 22, Gulou District, Nanjing, Jiangsu 210093, China. Tel./fax: +86 25 83685197. E-mail address: djia@nju.edu.cn (D. Jia). http://dx.doi.org/10.1016/j.tecto.2014.03.033 0040-1951/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Tectonophysics journal homepage: www.elsevier.com/locate/tecto