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Holocene Shortening Across the Main Frontal Thrust Zone in the Eastern Himalaya

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Holocene Shortening Across the Main Frontal Thrust Zone in the Eastern Himalaya Earth and Planetary Science Letters 357–358 (2012) 152–167 Contents lists available at SciVerse ScienceDirect Earth and Planetary Science Letters journal homepage: www.elsevier.com/locate/epsl Holocene shortening across the Main Frontal Thrust zone in the eastern Himalaya W. Paul Burgess a, An Yin a,n, Chandra S. Dubey b, Zheng-Kang Shen a, Thomas K. Kelty c a Department of Earth and Space Sciences and Institute for Planets and Exoplanets (iPLEX), University of California, Los Angeles, CA 90095-1567, United States b Department of Geology, Delhi University, Delhi 110007, India c Department of Geological Sciences, California State University at Long Beach, Long Beach, CA 90840-3902, United States article info abstract Article history: How plate-boundary processes control intra-continental deformation is a fundamental question in Received 10 May 2012 Earth sciences. Although it is long known that the active India–Asia convergence rate increases Received in revised form eastward, how this boundary condition impacts on active growth of the Himalaya is unclear. To address 22 September 2012 this issue, we conducted a geologic investigation of the Main Frontal Thrust (MFT), the largest and the Accepted 24 September 2012 most dominant active structure in the Himalayan orogen. Using the age and geometry of uplifted river Editor: P. Shearer 7 Available online 18 October 2012 terraces, we establish a minimum Holocene slip rate of 23 6.2 mm/yr along the decollement of the 10 km wide MFT zone in the far eastern Himalaya. This slip rate is partitioned on three structures: at Keywords: 8.4 mm/yr on the Bhalukpong thrust in the north, at 10 mm/yr across the growing Balipara Himalayan orogen anticline in the middle, and at 5 mm/yr on the Nameri thrust in the south. Our estimated minimum Main Frontal Thrust zone total shortening rate is significantly higher than the Holocene slip rate of 973 mm/yr for the MFT in active tectonics Himalayan tectonics the western Himalaya. However, this rate is similar to or potentially greater than the slip rate of 2171.5 mm/yr for the MFT in the central Himalaya. Our results support an early interpretation that active shortening across the Himalayan orogen is mostly accommodated by slip along the narrow MFT zone and its linked decollement beneath the Himalaya. The eastward increase in the Holocene MFT slip rate requires that the plate-boundary force rather than gravitational spreading is the fundamental control on active growth of the Himalayan orogen. & 2012 Elsevier B.V. All rights reserved. 1. Introduction The MFT in the eastern Himalaya links with the Sumatra subduction zone (e.g., Le Dain et al., 1984; Angelier and Baruah, The 2500 km Himalayan Main Frontal Thrust (MFT) zone is the 2009; Yin, 2010); both tectonic zones have hosted frequent and longest active contractional structure in the largest active collisional large (Ms48) magnitude earthquakes (Fig. 1C) (Tandon, 1955; orogen on Earth (e.g., Gansser, 1964; Nakata, 1989; Yeats et al., 1992; Seeber and Armbruster, 1981; Lay et al., 2005). Because of this, Bilham et al., 1998; Lave´ and Avouac, 2000; Avouac, 2003; Yin, 2006; establishing the structural framework and slip rate of the MFT in Yeats and Thakur, 2008)(Fig. 1A and B). Understanding the active the far eastern Himalaya is essential to understanding the spatial development of the MFT zone is a key for both unraveling the and temporal evolution of large seismic events along this linked mechanism of Himalayan growth (Avouac, 2003)andpreparingfor plate-boundary system. major earthquake disasters in the future (e.g., Tandon, 1955; Seeber Despite its importance, only a few preliminary studies have and Armbruster, 1981; Bilham, 1995, 2004; Bilham et al., 1997, 1998, focusedontheMFTintheeasternHimalaya(e.g.,Srivastava and 2001; Bilham and Ambraseys, 2005; Wesnousky et al., 1999; Lave´ Misra, 2008; Srivastava et al., 2009; Kumar et al., 2010; Chirouze et al., 2005; Feldl and Bilham, 2006; Szeliga et al., 2010; Kumar et al., et al., 2012). This situation is in a sharp contrast to the abundant and 2010). Available GPS data indicate that northeast India at longitude high-quality studies in the western and central Himalaya across the 921E currently moves at a rate of 38 mm/yr in the N251Edirection MFT (e.g., Baker et al., 1988; Jaswal et al., 1997; Powers et al., 1998; relative to stable Eurasia, whereas northwest India at longitude 761E Lave´ and Avouac, 2000; Kumar et al., 2006)(Fig. 1B). To address this moves at a rate of 35 mm/yr at N111E relative to stable Eurasia issue, we conduct geologic and geodetic studies to constrain Holo- (Zhang et al., 2004). cene and GPS slip rates across the MFT in the far eastern Himalaya. Our results indicate that the MFT slip rate in the eastern Himalaya is comparable and possibly higher to that in the central Himalaya but n Corresponding author. significantly higher than that in the western Himalaya. This observa- E-mail addresses: [email protected], [email protected] (A. Yin). tion supports a model that the active growth of the Himalayan 0012-821X/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.epsl.2012.09.040 W. Paul Burgess et al. / Earth and Planetary Science Letters 357–358 (2012) 152–167 153 36oN Major Research Sites of the MFT 2005 Mw 7.6 Kashmir EQ 1 Baker et al. (1988), Jaswal et al. (1997) 2 Powers et al. (1998) o 34 N ?? Mishmi Thrust 3 Wesnousky et al. (1999), Malik and Nakata (2003), Kumar et al. (2006) 1897 Mw = 8.1 Assam EQ 32oN 4 Lave and Avouac (2000), Lave et al. (2005) Yarlung Tsangpo/ 1950 Siang River Mw = 8.7 5 Kumar et al. (2010), Srivastava and Misra (2008) 1 1950 Mw 8.6 Metog EQ 30oN Metog 6 Kumar et al. (2010), Devi et al. (2011) 7 Kumar et al. (2010) 2 o M 4 5 6 28 N EQ 8 Srivastava et al. (2010) 3 ain 7 Fro nta o l T o 30 N hrust 8 26 N Siang R. MFT 1934 Mw = 8.2 Bihar EQ Sagaing 24oN o fault Srivastava et al. MFT 28 N Shillong Plateau 22oN (2009) 68oE 72oE 76oE80oE84oE88oE92oE 96oE 100oE Mishmi Thrust 1950 Mw = 8.7 Metog Earthquake a Eastern y Himalayan Indochina la Thrust a Zone Him tern Srivastava and Misra Eas (2008) Assam Valley Valley Devi et al (2011) r 10oN Gulf of Subansiri R. e Thailand v Assam o i 27 N Tipi Thrust R 27oN a tr Trench site of u Naga Hills MFT p Kumar et al. (2010) a hm 2004 Mw = 9.1 Fig. 2. Bha- Kameng R. Bra Sumatra Earthquake lukpong site 0 25 50 km Sumatra Subduction of this study Trench site of Kumar et al. (2010) 90oE Zone 93oE 94oE 95oE 96oE 97oE Fig. 1. (A) Major active structures of the eastern Himalayan frontal zone and sites of previous research on Quaternary chronology and active deformation of the MFT zone. Our study area is indicated by the location of Fig. 2. (B) Sites of major historical earthquakes following Chen and Molnar (1977) and Kashmir earthquake following Hussain et al. (2009). Also shown are most relevant studies on the Main Frontal Thrust zone by early workers (see text for detailed description). (C) Tectonic relationship between the eastern Himalayan convergence zone including structures bounding the Shillong plateau and the Sumatra subduction zone. orogen is mainly controlled by the velocity boundary condition rate (e.g., Molnar and Stock, 2009; Copley et al., 2010). This in turn imposed by the India–Asia convergence rather than by gravitational would support the notion that active growth of the Himalaya is spreading of the Himalayan-Tibetan orogen. mainly controlled by the plate-velocity boundary condition rather than gravitational spreading (see a recent review on this issue by Li and Yin, 2008 and an insight from a simple analog model in Yin and 2. Regional geology Taylor, 2011). 2.1. Quaternary slip rates on the MFT 2.2. Tectonic setting of the eastern Himalaya The intense work on the MFT zone in the western and central Since the pioneering work of Jangpangi (1974) and Gansser Himalaya (e.g., Bilham et al., 1998; Lave´ and Avouac, 2000; Yeats and (1983), the Bhutan Himalaya has been studied intensely in the Thakur, 2008) may in part be attributed to the better constraints on past five decades (Ray et al., 1989; Swapp and Hollister, 1991; the ages of Late Cenozoic strata (e.g., Burbank et al., 1996; Ojha et al., Ray, 1995; Bhargava, 1995; Edwards et al., 1996; Grujic et al., 2000, 2009; White et al., 2002). In Pakistan, the shortening rate 1996, 2002, 2006; Davidson et al., 1997; Stuwe¨ and Foster, 2001; across Himalayan frontal structures is estimated to be 1474mm/yr Daniel et al., 2003; Tangri et al., 2003; Carosi et al., 2007; Meyer over the past 5 Ma (Baker et al., 1988; Jaswal et al., 1997)(Fig. 1B). et al., 2006; Richards et al., 2006; Drukpa et al., 2006; Hollister The shortening is mostly concentrated on the MFT, with a minor and Grujic, 2006; McQuarrie et al., 2008; Kellett et al., 2009, 2010; component partitioned by active faulting in the Himalayan interior Long and McQuarrie, 2010; Long et al., 2011a,b; Chambers et al., (Kaneda et al., 2008; Hussain et al., 2009). In NW India, a Pliocene- 2011). A minimum north–south shortening of 350 km since Quaternary shortening rate of 1474 mm/yr was estimated across 22 Ma yields an average minimum shortening rate of 16 mm/yr the MFT and its hanging-wall structures (Powers et al., 1998).
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