Kinematics of the Greater Himalayan sequence, Dhaulagiri Himal ...

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$Fayek & Kyser 2000 uraninite fractionations.pdf - Queen's University$

285 286 This interpretation is supported by preliminary early Proterozoic zircon ages for the Ulleri augen orthogneiss of ca. 1831 Ma (DeCelles et al. 2000). 287 288 289 290 291 292 293 294 295 296 297 298 299 Tertiary leucogranite melt is present throughout the upper portion of the Greater Himalayan sequence in the Dhaulagiri Himalaya, and reflects at least two episodes of melt generation. Kyanite-grade melt from near the STDS at the top of the Greater Himalayan sequence has yielded Eohimalayan ages (35-32) from U-Pb analyses of zircon (Godin et al. 1999a; 2001). This melt is thought to have formed in response to initial tectonic burial of the Indian plate beneath Asia (Godin et al. 1999a, 2001). In the middle portion of the Greater Himalayan sequence in the Kali Gandaki valley, a slightly deformed leucogranitic dyke has been dated by U-Pb zircon analyses as ~22 Ma (Nazarchuk 1993). This is Neohimalayan in age, and the dyke may have formed as a result of decompressional melting during extrusion of the Greater Himalayan sequence from mid-crustal levels (Vannay & Hodges 1996; Godin et al. 2001). The spatial distribution and relative extent of each generation of melt within both the Dhaulagiri Himal and the Himalayan orogen in general is not known; however, ages from similar rocks in parallel transects across the Himalaya are predominantly Miocene (Godin et al. 2006a). 300 301 302 303 304 305 The total amount of Tertiary melt within the Greater Himalayan sequence in the Kali Gandki valley is significantly less than in other portions of the orogen such as the Manaslu (Pêcher 1989) and Khumbu regions (Bordet 1979). The variation in along-strike melt volume may reflect a difference in the positions of the exposures measured parallel to the transport direction (Pêcher 1989). Regions with abundant Tertiary melt may reflect a more hinterland transect of the Greater Himalayan sequence. 306 3.4 Main Central thrust 14
307 308 309 310 311 312 In this study we follow Searle et al. (2008) and map the MCT as a fault below the transposed planar features and pervasive top-to-the south ductile deformation that characterizes the Greater Himalayan sequence. In the Dhaulagiri Himal the MCT separates unmetamorphosed-to low metamorphic grade sedimentary rocks, in which features such as ripple marks and trough crossbeds are preserved, from pervasively deformed rocks above in which all primary features have been transposed. 313 3.5 Lesser Himalayan sequence 314 315 316 317 318 319 The rocks below the MCT in the Dhaulagiri Himal consist of chloritic phyllites and intercalated quartz arenite of the Kunchha Formation. The phyllitic rocks are characterized by multiple cleavages while the sandstones preserve sedimentary cross-bedding and oscillation ripples (Hodges et al. 1996). The preservation of pristine sedimentary structures and the lack of transposition of planar and linear features suggest that the amount of ductile strain in these rocks is significantly less than those above the MCT. 320 4. Microstructures and quartz c-axis fabrics 321 322 323 324 325 326 327 328 Quartz c-axis fabrics have been used to characterize the strain and kinematic behaviour of parts of the Greater Himalayan sequence in various localities along the orogen including the STDS in the Everest region (Law et al. 2004), the exhumed migmatitic high-grade metamorphic core in Bhutan (Grujic et al. 1996), and the deformed extruded Greater Himalayan sequence of northwestern India (Grasemann et al. 1999; Bhattacharya & Weber 2004). In central Nepal quartz c-axis fabrics from the Greater Himalayan sequence in the Modi, Madi, Chepe, Darondi, and Budhi Gandaki valleys (Figure 1c), were first reported by Bouchez & Pêcher (1976) and subsequently revisited by Bouchez (1978), and Bouchez & Pêcher (1981). Within these studies, 15
Page 1 and 2: 1 2 3 4 5 Kinematics of the Greater
Page 3 and 4: 39 1. Introduction 40 41 42 43 44 4
Page 5 and 6: 84 85 86 87 88 provide new insight
Page 7 and 8: 129 130 131 132 133 134 135 The Dha
Page 9 and 10: 173 3.3 Greater Himalayan sequence
Page 11 and 12: 218 219 220 221 222 8 cm apart. In
Page 13: 263 quartzite and, locally, more im
Page 17 and 18: 352 4.1 Quartz petrofabric analysis
Page 19 and 20: 398 399 400 401 402 403 404 405 406
Page 21 and 22: 443 444 445 446 447 448 449 maximum
Page 23 and 24: 488 489 490 491 492 the X-Z plane o
Page 25 and 26: 534 535 through the following equat
Page 27 and 28: 572 573 574 575 576 577 578 579 val
Page 29 and 30: 617 618 619 620 621 622 623 624 625
Page 31 and 32: 663 6.3 Flow kinematics 664 665 666
Page 33 and 34: 709 710 711 712 713 714 715 716 717
Page 35 and 36: 753 754 better understand the proce
Page 37 and 38: 765 766 References 767 768 769 770
Page 39 and 40: 830 831 832 833 834 835 836 837 838
Page 41 and 42: 900 901 902 903 904 905 906 907 908
Page 43 and 44: 970 971 972 973 974 975 976 977 978
Page 45 and 46: 1039 1040 1041 1042 1043 1044 1045
Page 47 and 48: 1107 1108 1109 1110 1111 1112 1113
Page 49 and 50: 1163 1164 1165 1166 1167 a leucogra
Page 51 and 52: 1205 1206 1207 1208 1209 plotted ag
Page 53 and 54: 1247 1248 1249 1250 1251 1252 1253
Page 55 and 56: 83˚ 30'E South Tibetan Detachment
Page 57 and 58: A Previous Studies (Central Nepal)
Page 59 and 60: SW NE NW SE A B W E W E C D
Page 61 and 62: 018 015 grain shape foliation 038 2
Page 63 and 64: SW A S Qtz C Qtz Ep Am Am Am Ms 200
Page 65 and 66:
10 percent pure shear 80 70 60 50 4
Page 67:
(A) percent pure shear 60 50 40 30
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