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

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

375 376 pattern with a slight top-to-the-southeast shear sense (Figure 8). The crystallographic preferred orientation pattern of c-axes in this specimen reflects dominant prism slip. 377 378 379 380 381 382 383 384 385 386 387 388 389 390 Specimen 038 was sampled from a chlorite quartz schist. Chlorite comprises 65-70 % of the rock and defines the foliation, which strikes 309˚ and dips 56˚ to NE, and the lineation, which plunges 51˚ towards 024˚. Quartz and a minor opaque phase make up the other 30-35%. Quartz in the specimen exhibits a moderate foam texture, indicative of grain boundary migration, and minor undulose extinction. The size of the quartz crystals is everywhere constrained by the distance between chlorite partings, which also suggests recrystallization through grain boundary migration. Specimen 038 does not yield an organized c-axis pattern and instead is characterized by a random scattering of quartz c-axis (Figure 8). The lack of a preserved quartz c-axis pattern may be the result of significant post-kinematic recrystallization, however, rocks both structurally above and below specimen 038 are characterized by well-developed quartz crystal latticepreferred orientations. Alternatively, strain may have been preferentially partitioned into the thick chlorite layers present in the rock such that the quartz crystals were not subject to enough strain to cause alignment of their c-axis. Similar results have been observed in calc-silicate gneiss samples (Figure 7) where strain may have been preferentially accommodated by calcite. 391 392 393 394 395 396 397 Specimens 049, 053, 070B, and 78 were sampled from outcrops of mylonitic quartzite. In these specimens (Figures 7 and 8) the lineation is defined by the alignment of muscovite aggregates on foliation surfaces that are defined by quartz grain-shape fabrics and thin muscovite partings. Locally, muscovite also lies along and defines weakly-developed extensional shear bands and S-planes with a top-to-the-southwest shear sense. Quartz grains exhibit subgrain formation, bulging and minor foam textures indicative of subgrain rotation and grain boundary migration that is transitional between recrystallization regimes 2 and 3 of Hirth & Tullis (1992). 18
398 399 400 401 402 403 404 405 406 407 408 Specimens 049, which contains a foliation that strikes 315˚ and dips 54˚ to the NE and a lineation that plunges 50˚ towards 035˚, and 053, which contains a foliation that strikes 325˚ and dips 45˚ to the NE and a lineation that plunges 42˚ towards 056˚, were sampled from the same structural level at different locations. Specimen 049 yields a well-defined, asymmetric, type-I cross-girdle quartz c-axis pattern dominated by rhomb and prism slip with a top-to-thesouth shear sense (Figure 8). Specimen 053, in contrast appears to define a type-I crossedgirdled pattern with predominant rhomb slip (Figure 8); no dominant asymmetry is apparent. Specimen 070B, which contains a foliation that strikes 242˚ and dips 18˚ to the NNW and a lineation that plunges 8˚ towards 025˚, was sampled from a lower structural position than 049 and 053. It yields a rhomb-dominated well-defined, asymmetric, type-I cross-girdle quartz c- axis pattern with a top-to-the-south shear sense (Figure 8). 409 410 411 412 413 414 415 416 417 418 Specimen 073 (Figure 8) was collected from the mylonitic Ulleri augen gneiss (Figures 2, 7) near the base of the Greater Himalayan sequence. Foliation in the augen gneiss is defined by muscovite and biotite alignment and quartz grain-shape fabrics that strike 292˚ and dip 15˚ to the NNE, and is characterized by strongly developed C/S/C’ fabrics with a top-to-the-south shear sense; lineations are defined by quartz rods that plunge 15˚ towards 022˚. Quartz in the sample is characterized by subgrain boundaries, undulose extinction, and bulging, which are characteristic of subgrain rotation and grain boundary migration, transitional between Regime 2 and 3 of Hirth & Tullis (1992). Quartz c-axis orientations define a moderately well-developed, single inclined girdle with a strong asymmetry that suggests a top-to-the-south shear sense. Prism and rhomb slip dominate this fabric. 419 420 In the structurally lowest specimen, 078, from the base of the Greater Himalayan sequence (Figure 7), quartz c-axes define a type-I cross-girdled pattern, dominated by basal 19
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 and 14: 263 quartzite and, locally, more im
Page 15 and 16: 307 308 309 310 311 312 In this stu
Page 17: 352 4.1 Quartz petrofabric analysis
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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