Exhumation history and faulting activity of the southern segment of the Longmen Shan, eastern Tibet Xi-Bin Tan a , Yuan-Hsi Lee b,⇑ , Wen-Yu Chen b , Kristen L. Cook c,d , Xi-Wei Xu a a Institute of Geology, China Earthquake Administration, Beijing 100029, China b Department of Earth and Environmental Sciences, National Chung-Cheng University, Taiwan, ROC c Department of Geosciences, National Taiwan University, Taiwan, ROC d German Research Center for Geosciences GFZ, Potsdam, Germany article info Article history: Received 13 June 2013 Received in revised form 22 November 2013 Accepted 2 December 2013 Available online 12 December 2013 Keywords: Eastern Tibet Longmen Shan Exhumation history Low temperature thermochronology Fission track abstract The Longmen Shan (LMS), which constitutes the eastern border of the Tibetan Plateau, is about 400 km in length and characterized by a steep topographic transition from the Sichuan Basin to the plateau. The 2008 M w 7.9 Wenchuan earthquake and 2013 M w 6.6 Lushan earthquake were associated with the central to northern segments and southern segment of the LMS fault belt, respectively. In this paper, zircon and apatite fission track (ZFT and AFT, respectively) dating in combination with previously published low temperature thermochronology studies are used to constrain both the exhumation history and fault activity along the LMS, with a special focus on the southern segment. In the southern segment of the LMS, the ZFT ages in the hanging wall of the Wulong-Yanjing fault 10–14 Ma, increasing to ca. 30 Ma to the northwest of the faults and to 100–200 Ma in the plateau region. The AFT ages are 3–5 Ma at the mountain front and increase to 8–26 Ma in the plateau. We show that these age distributions are con- trolled by fault geometry. Two stages of rapid exhumation were identified using apatite fission track length modeling and the age distributions in the southern segment of the LMS. The first stage is from ca. 30 Ma and the second stage is from 3–5 Ma to present. In contrast with the middle segment of the LMS, the Cenozoic exhumation rate is higher in the southern segment of the LMS, which may be due to the influence of the collision between the India and Eurasia plates and/or different faulting mecha- nisms in the different segments. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction The Longmen Shan (LMS) constitutes the eastern boundary of the Tibetan Plateau (Fig. 1a). It is about 400 km in length and is characterized by a steep topographic transition from 600 m (the Sichuan Basin) to about 5000 m (the Tibet plateau), in about 50 km. In contrast to the more substantial shortening rate of the Himalayas, the shortening rate across the LMS is less than 3 mm/ yr based on GPS (Global Positioning System) and 10 years of geod- esy data collected prior to the May 12th 2008 Wenchuan earth- quake, Sichuan (King et al., 1997; Chen et al., 2000; Gan et al., 2007). The 2008 Wenchuan earthquake (M w 7.9) was one of the most devastating earthquakes in China’s history, resulting in over 80,000 fatalities, extreme economic loss, and leaving more than 1.5 million people homeless (Stone, 2008). Research has shown that two major faults were active during the Wenchuan earth- quake, the Beichuan-Yingxiu fault and Jiangyou-Guanxian fault, which are located in the central to northern segments of the LMS (Xu et al., 2009). The rupture of the Wenchuan earthquake did not extend to the southern segment of the LMS. However, the dis- placement rate (from GPS measurements) in the southern segment of the LMS appears to be similar or even greater than that in the north (Chen et al., 2000)(Fig. 1a). Recently, a M w 6.6 earthquake oc- curred at the southern tip of the LMS, resulting in 196 fatalities and extensive damage to property and infrastructure (Xu et al., 2013). To better assess the potential for disastrous earthquakes in this re- gion, it is important to understand the area’s Cenozoic exhumation history and fault activity. Cenozoic deformation in the LMS region has been produced by the eastward growth of the Tibetan Plateau, caused by the collision of the India and Eurasian plates starting at 50 Ma (Yin and Harri- son, 2000). The collision has progressively propagated north and eastward (Yin and Harrison, 2000; Tapponnier et al., 2001). Previous studies have shown that the central segment of the LMS experienced rapid exhumation starting at 12–5 Ma (Kirby et al., 2002; Godard et al., 2009); furthermore, Wang et al. (2012) found an earlier exhumation event at 30–25 Ma. Topographic profiles show that the southern and central segments of the LMS form a sharp, steep boundary with the Sichuan Basin, while topography 1367-9120/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jseaes.2013.12.002 ⇑ Corresponding author. Tel.: +886 52720411x66212; fax: +886 52720807. E-mail address: seilee@eq.ccu.edu.tw (Y.-H. Lee). Journal of Asian Earth Sciences 81 (2014) 91–104 Contents lists available at ScienceDirect Journal of Asian Earth Sciences journal homepage: www.elsevier.com/locate/jseaes