Partitioning of India‐Eurasia Convergence in the Pamir‐Hindu Kush from GPS Measurements S
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GEOPHYSICAL RESEARCH LETTERS, VOL. 37, L04305, doi:10.1029/2009GL041737, 2010 Click Here for Full Article Partitioning of India‐Eurasia convergence in the Pamir‐Hindu Kush from GPS measurements S. Mohadjer,1 R. Bendick,1 A. Ischuk,2 S. Kuzikov,3 A. Kostuk,3 U. Saydullaev,2 S. Lodi,4 D. M. Kakar,5 A. Wasy,6,7 M. A. Khan,8 P. Molnar,9 R. Bilham,9 and A. V. Zubovich10 Received 11 November 2009; revised 30 December 2009; accepted 14 January 2010; published 24 February 2010. [1] Convergence of 29 ± 1 mm/yr between the NW corner formation in continental lithosphere [e.g., Bürgmann and of the Indian plate and Asia is accommodated by a Dresen, 2008; England et al., 1985]. Oceanic lithosphere, combination of thrust and strike‐slip faulting on prominent where plate tectonics works well, has a relatively simple faults and apparent distributed deformation within the vertical strength profile with little lateral variation, such that Hindu Kush, Pamir, South Tien Shan and Kohistan relative plate motion is entirely accommodated in narrow Ranges. An upper bound to the slip rate of known faults fault zones, and plate interiors are effectively rigid. Defor- is obtained by ignoring distributed strain and rotation: mation of continental lithosphere, in contrast, seems to re- convergence occurs on thrust faults north of the Peshawar flect a range of vertical strength profiles, depending on Basin(13±1mm/yr)andintheAlai‐South Tien Shan laterally varying temperature and composition. Therefore, (12 ± 2 mm/yr), and shear on the northeast‐trending the mechanisms by which continents respond to tectonic northern Chaman‐Gardiz‐Konar system (18 ± 1mm/yr) forces must have length‐scale dependence [England et al., and the Darvaz‐Karakul fault zone (11 ± 2 mm/yr). Slip 1985], as different mechanical properties are sampled at rates on the Herat and Talas‐Ferghana faults are small different scales. For example, at the length scale (normal to (<2 mm/yr). Shortening not attributable to known active strike) of single continental faults (∼10 km), the behavior of faults occurs within the Hindu Kush and central Pamir continental crust can be described using the accumulation (16 ± 2 mm/yr) with concomitant east‐west extension in and release of elastic deformation on the faults [Okada, the latter of 9 ± 2 mm/yr. This diversity of strain styles 1985]. At the scale of a single mountain range (∼100 km), confirms the importance of mechanical heterogeneity to as in Taiwan, the underthrusting of a wedge of effectively continental tectonics and shows that the Pamir, although plastic material (brittle deformation obeying Coulomb fric- less than half the size, behaves more like Tibet than like a tion) can account for the topography and the dynamics [e.g., linear belt of localized deformation. Citation: Mohadjer, S., Dahlen et al., 1984]. At the length scale of the Tibetan et al. (2010), Partitioning of India‐Eurasia convergence in the Plateau (∼1000 kilometers), the deformation of a thin viscous Pamir‐Hindu Kush from GPS measurements, Geophys. Res. sheet can match the hypsometry and strain rate field of the Lett., 37, L04305, doi:10.1029/2009GL041737. whole plateau, demonstrating that the vertically averaged constitutive relation is viscous [e.g., England and McKenzie, 1. Introduction 1982; England and Houseman, 1986]. The region of central Asia encompassing NW Pakistan, Afghanistan, Tajikistan, [2] Spatially varying deformation mechanisms in conti- and Kyrgystan (Figures 1 and S1), containing an actively nental collision zones are significant to the general study of deforming region, the Pamir, affords an opportunity to in- continental tectonics, because they help to constrain the vestigate whether scale dependence including viscous dy- relationship between rheology and the localization of de- namics is important regions of lengths less than 1000 km.11 Geodetic observations of the region also constrain the re- 1Department of Geosciences, University of Montana, Missoula, gional kinematics, including slip rates on several very large Montana, USA. faults. 2Tajik Institute of Earthquake Engineering and Seismology, Dushanbe, Tajikistan. 2. Methods 3Research Station of the Russian Academy of Sciences, Bishkek, Kyrgyzstan. [3] We installed a network of GPS sites in the area 4 Department of Civil Engineering, NED University of Engineering (Tables 1 and Table S1) between 30° and 44°N latitude and and Technology, Karachi, Pakistan. 5Department of Geology, University of Baluchistan, Quetta, Pakistan. between 60° and 76°E longitude (Figure S1) including 6Afghan Geological Survey, Kabul, Afghanistan. eastern Afghanistan, Tajikistan, northwestern Pakistan, 7Deceased 1 October 2009. Baluchistan, and western Kyrgyzstan. Geodetic measure- 8National Centre of Excellence in Geology, University of Peshawar, ments at these new sites are supplemented with observa- Peshawar, Pakistan. 9Department of Geological Sciences, University of Colorado at tions from two IGS (International GNSS Service) sites, Boulder, Boulder, Colorado, USA. KIT3 in Uzbekistan and POL2 in Kyrgyzstan. All of the 10Department of Technology Infrastructures and Management of sites with velocities reported here (Table 1 and Figure 1) the Information, Central Asian Institute for Applied Geosciences, operate continuously with the exception of Kabul (KBUL), Bishkek, Kyrgyzstan. 11Auxiliary material are available in the HTML. doi:10.1029/ Copyright 2010 by the American Geophysical Union. 2009GL041737. 0094‐8276/10/2009GL041737$05.00 L04305 1of6 L04305 MOHADJER ET AL.: GPS IN THE PAMIR REGION L04305 Figure 1. Locations of major active faults (heavy black lines), inactive faults (fine lines), and GPS velocity vectors with respect to Eurasia fixed reference frame from this study in red. The purple vector is transformed from [Gan et al. 2007]. The error ellipses represent 95% confidence. Abbreviations of fault names: TD, Tajik Depression; TFF, Talas‐Ferghana Fault; SGF, South Gissar Fault; DkF, Darvaz‐Karakul Fault; MPT, Main Pamir Thrust; MAT, Main Alai Thrust; CbF, Central Badakhshan Fault; HF, Herat Fault; CF, Chaman Fault; GF, Gardiz Fault; KoF, Konar Fault; ONF, Ornach‐Nal Fault; MF, Mokur Fault; KF, Karakoram Fault; MBT, Main Boundary Thrust; and MKT, Main Karakoram Thrust. Other geographic names used in the text are shown in Figure S1. which was occupied for 93 days in 2006 and 10 days in series of site positions (Figure S3) were used to estimate site 2008 (Table S1). See auxiliary material for site details. velocities in ITRF05 [Altamimi et al., 2007] and Eurasia‐ [4] Site position estimates were calculated for each day fixed (Table 1) and India‐fixed reference frames (Table S2) with the GAMIT software package [Herring et al., 2006] in using GLOBK [Herring et al., 2006]. More details are a loosely constrained global reference frame including 14 provided in the auxiliary material. IGS sites aside from POL2 and KIT3. The resulting time Table 1. Station Coordinates and Velocitiesa Longitude Latitude East (mm/yr) North (mm/yr) Site (deg.) (deg.) ITRF05 Eurasia ITRF05 Eurasia KBUL 69.130 34.574 28.2 ± 1.1 −0.1 ± 1.1 14.2 ± 1.1 10.0 ± 1.1 QTAG 66.991 30.166 26.8 ± 1.0 −1.4 ± 1.0 23.6 ± 1.0 18.8 ± 1.0 NCEG 71.487 34.004 27.7 ± 0.9 −0.8 ± 0.9 32.5 ± 0.9 29.0 ± 0.9 MANM 71.680 37.542 17.7 ± 1.1 −10.7 ± 1.1 19.3 ± 1.1 15.8 ± 1.1 SHTZ 68.123 37.562 −5.5 ± 1.1 22.7 ± 1.1 8.3 ± 1.1 3.9 ± 1.1 GARM 70.317 39.006 27.0 ± 1.2 −1.2 ± 1.2 6.2 ± 1.2 2.4 ± 1.2 OSHK 72.777 40.530 27.7 ± 1.3 −0.6 ± 1.3 7.2 ± 1.3 4.0 ± 1.3 KCHI 67.113 24.931 33.6 ± 0.7 5.6 ± 0.7 32.7 ± 0.7 28.0 ± 0.7 IAOH 78.973 32.779 27.0 ± 1.6 −1.7 ± 1.6 18.0 ± 1.6 16.6 ± 1.6 RSCL 77.600 34.128 22.9 ± 1.2 −5.7 ± 1.2 22.2 ± 1.2 20.3 ± 1.2 TASHb 75.230 37.770 N.D.c −1.9 ± 1.8 N.D. 22.5 ± 1.7 KIT3 66.885 39.135 28.2 ± 0.8 0.1 ± 0.8 3.4 ± 0.8 −1.4 ± 0.8 POL2 74.694 42.680 26.4 ± 0.8 −1.8 ± 1.6 4.8 ± 0.8 2.1 ± 0.8 aITRF05 – Eurasia pole is 55.873° ± 0.7°N, −95.825° ± 0.8°E, 0.258° ± 0.003 °/Ma. bData for TASH is from Gan et al. [2007]. cN.D. = no data. 2of6 L04305 MOHADJER ET AL.: GPS IN THE PAMIR REGION L04305 Figure 2. Map of the study area showing localities where observations of Quaternary offsets (orange open circles), geo- logic slip rates of known locality (orange stars), geologic slip rates of unknown locality along faults (orange rectangles), and geodetic slip rates of known locality (green stars) have been made. Data and fault locations are from [Abdrakhmatov et al. 1996], Ambraseys and Bilham [2003], Arrowsmith and Strecker [1999], Banerjee and Bürgmann [2002], Burtman et al. [1996], Burtman and Molnar [1993], DeMets et al. [1990], Guseva [1986], Jade et al. [2004], Konopaltsev [1971], Lawrence et al. [1992], Legler and Przhiyalgovskaya [1979], Nikonov [1970], Nikonov et al. [1983], Reigber et al. [2001], Ruleman et al. [2007], Sborshchikov et al. [1981], Shareq and Chmyriov [1977], Trifonov [1978], Wellman [1966], Wolfart and Wittekindt [1980], and [Wright et al. 2004]. [5] To estimate the parallel and normal components of calculating a local transformation (north and east adjust- slip rates on major faults (Table S3) and to compare them to ments) between our Eurasia‐fixed frame and the Eurasia‐ geologic slip rates (Figure 2), we first compiled major faults fixed frame of Gan et al.