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84 south to 18 Ma in the north; the exhumation rates increase in the same direction. Such an age pattern can be explained by: (1) A piggy-back thrust tectonics in which footwall burial and hangingwall exhumation propagated towards north. (2) Since the Karakul- Mazar belt may behaved as a rigid block during the Tertiary, deformation was probably confined to the margins of the belt, e.g. to the right-lateral Markansu fault to the north of the belt. (3) The whole belt may be rotated around a horizontal axis with normal faulting in the south and thrusting in the north. (4) Cretaceous collision south of the Pamirs led to further compression and induced renewed continental subduction of the Karakul-Mazar belt beneath the Central Pamirs and thermally influenced the apatite annealing zone in the Karakul lake area. (b) The Central Pamiran Qiangtang block is characterised by a Tertiary anticlinorium and constitute the Muzkol and Sares domes. The basement rocks exposed in the domes are interpreted as the Triassic/Jurassic Karakul-Mazar/Sonpan-Ganze accretionary wedge rocks (Schwab et al. in press). During the Tertiary, these rocks were strongly deformed and metamorphosed to upper amphibolite facies conditions with local migmatisation. Rb/Sr whole rock-muscovite ages from two gneiss samples of the Sares dome yielded 37 and 30 Ma. Emplacement ages of Tertiary melts seem to be episodic: An earlier phase with subalkaline intrusions is of Early Oligocene age (~33 Ma) and a later phase with aplitic dykes of Late Miocene ages (~14-11 Ma). Metamorphic hornblende and biotite Ar/Ar cooling ages cover ~28-14 Ma. Tertiary melt generation is also documented by widespread basalt dyke occurrence in the domes with Ar/Ar whole rock ages at ~20 Ma. Apatite and zircon fission track ages range from 20 to 15 Ma. The Tertiary anticlinorium is not only characterised by penetrative resetting of nearly all mineral chronometers, but also shows very fast exhumation rates. Between 22 and 15 Ma cooling rates increased to > 40°C/Ma and in some cases (e.g. P15) all mineral ages are reset to ~15 Ma. Tertiary intramontane basins along the margins of the dome contain coarse grained conglomerates mainly composed of weakly metamorphosed carbonatic and dolomitic clasts of the Mesozoic cover sequence of the dome. Reset zircons of sediments from a basin south of the dome yielded ages of 20 to 19 Ma. Basalts cutting through the section are preliminarily interpreted as of within plate origin. They yielded ~20 Ma Ar/Ar whole rock ages. K/Ar sericite ages range from 33 to 14 Ma and increase away from the dome (from north to south). The older K/Ar sericite ages (>25 Ma) are interpreted to be partly reset. Dome exhumation between 25 to 15 Ma seem to have heated the Palaeogene sedimentary basin. (c) The southernmost samples evaluated for their low-T history are Cretaceous intrusions attributed to the Shyok arc. At least since Miocene the northernmost South Pamirs was strongly deformed along the right lateral splays of the Karakoram fault. The transpressional faults seem to be responsible for exhumation at 11-10 Ma. From Late Miocene to Recent, final cooling of the samples was at rates of 5-16°C/Ma. (d) A coeval Late Miocene (11-10 Ma) denudation is indicated in the southernmost Tien Shan by apatite fission track data on granitoids. There, exhumation was probably induced in response to crustal thickening along major thrust faults and dextral transpressional strike slip faults. In the Central Pamirs, future work has to determine if metamorphism, melt generation and deformation occurred in two major phases, namely in Early Oligocene and Early Miocene, and if exhumation in the whole Pamirs was a constant steady-state Tertiary process, or with distinct accelerated exhumation phases, e.g. at the beginning of the Middle and Late Miocene.
5 Summary This thesis results in a fundamental new understanding of the pre-Tertiary accretion-collision history of the Pamirs. Based on determinations of age and origin of magmatic belts from the southernmost Tien Shan to the eastern Pamirs, it is for the first time possible to relate Pamiran units to those from Tibet and Afghanistan. Furthermore, this study constrains the Tertiary low-T cooling history of the Pamirs induced by the India-Asia collision. In combination, the understanding of accretion, collision, and magmatic activity, the definition of distinct units and their margins, help to relate low-T cooling of the upper crust to probably rheologically weakened crust caused by older deformational and thermal events. Successive southward enlargement of Eurasia started with the accretion of the northern, central, and southern continental and oceanic terranes in Early to Middle, and Late Palaeozoic times. The Early Permian (~277 Ma) syn- to postcollisional magmatic rocks of the southernmost Tien Shan are attributed to Early Permian closure of the South Gissar/South Tien Shan ocean and correlated with the Garm-Turkestan- Alay granitoids. The Baysunta and Garm basements are interpreted as part of the Tadjik continental block that is probably connected to the Tarim block. Further amalgamation was along the southern margins of the Tadjik/Tarim continental blocks. The Sonpan-Ganze oceanic basin subducted northward below the composite Early and Late Palaeozoic/Triassic Kunlun arcs. The ~370-330 Ma old metavolcanic rocks (Altyndara section) are interpreted as representatives of the north Kunlun arc. These rocks likely extends into the Triassic, probably in a back-arc setting due to continued northward subduction in the second arc stage of the Permo-Triassic. Late Triassic to Early Jurassic (~227-199 Ma) post-tectonic granitoids in northwestern Tibet and a massive ~227 Ma Karakul lake batholith in the Pamirs stitch the Karakul-Mazar complex together. Like aged, widely distributed Triassic plutonites and Permo-Triassic volcano-sedimentary successions are described from the western Badakshan, western Hindu Kush, and Feroz Koh regions. The cryptic Tanymas suture between the Northern and Central Pamirs is part of the Jinsha suture. The Tanymas/Jinsha suture developed by southward subduction of the Sonpan-Ganze ocean below the Central Pamirs/Qiangtang block. Subduction on the northern and southern margins (recent positions) of this ocean caused extensive accretion-subduction complexes, determined in the Central Pamirs as Karakul-Mazar accretionary wedge complex and is correlated with the Sonpan-Ganze mélange in Tibet. In the Central Pamirs and Qiangtang, Tanymas/Jinsha oceanic crust and metamorphosed Karakul-Mazar/Sonpan-Ganze mélange is exposed in regional anticlinoria. These basement domes may extend into the Safed Khers. Zircons from basement rocks of Central Tibet and inherited zircons from a Pamiran Qiangtang block granitoid have similar 575-425 Ma ages and may constitute typical Gondwanan crustal ages. Arc-type granitoids that cut the southern Qiangtang block (~170-160 Ma) and granitoids that intrude into the eastern Pshart oceanic-basin-arc sequence (~190-150 Ma) constitute the Rushan Pshart arc which is correlated with the Bangong-Nujiang zone to the east and the Khas Rod in the west. 85
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Institut für Geowissenschaften (IF
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Key words: Tien Shan, Pamirs, Tibet
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* Nr. 22 MESCHEDE, M. (1994): Tecto
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* Nr. 55 REINECKER, J. (2000): Stre
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The amalgamation of the Pamirs and
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Wer aber je auf Asiens Erdboden sch
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viii (1971). Black lines with arrow
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x sample locations and age distribu
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xii Swedish expeditions followed. I
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2 postulated that the Safed Khers a
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4 Zusammenfassung Die paläozoische
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6 (d) Oberkreide Spaltspurenalter w
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8 deformation propagate from the pl
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10 source terrains, changes in the
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12 Geochemisches Zentrallabor, Univ
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14 mean UO+/U+ and Pb+/U+ value. Si
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16 apatites and zircons were counte
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18 number of simulation runs and th
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Two Palaeozoic sutures divide the C
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igneous and sedimentary rock sequen
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Triassic and the formation of an is
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27 Lake Karakul The Lake Karakul ar
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3.3.2 Major and trace elements Majo
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32 of 26-40 for samples P2, P5, and
Page 58 and 59: 34 some of the zircons suffered Pb
Page 60 and 61: 36 fractions are situated close to
Page 65: 3.4.2 Rb/Sr dating The Rb/Sr minera
Page 69 and 70: 45 The Cretaceous plutons show mode
Page 72 and 73: 48 Thompson et al. (1984), who see
Page 74 and 75: 50 granites and have Sm-Nd model ag
Page 76 and 77: 52 associations in Afghanistan is f
Page 78 and 79: 54 Kara Kunlun or Mazar accretionar
Page 80 and 81: 56 Early Jurassic low-angle normal
Page 82 and 83: 58 Coward et al. (1988) pointed out
Page 84 and 85: 60 oceanic crust for the consumptio
Page 86 and 87: 62 Palaeogene volcanic rocks of cen
Page 88: 64 3.7 Conclusions Based on new own
Page 91 and 92: 4 Cenozoic exhumation history of th
Page 93 and 94: Southern Tien Shan One Permian gran
Page 97 and 98: Thermal modelling The results of th
Page 99 and 100: amphibole, white mica, and biotite
Page 101 and 102: the zircon PAZ. The apparent apatit
Page 103 and 104: elt likely operated as an out-of-se
Page 105: ages from gneissic rocks within the
Page 110 and 111: 86 Cretaceous plutons that intrude
Page 112 and 113: 88 6 References Allègre C.J., Cout
Page 114 and 115: 90 House, scale 1:2 000 000. Chen F
Page 116 and 117: 92 Karakorum (Sinkiang, China); the
Page 118 and 119: 94 Hurford A.J. and Hammerschmidt K
Page 120 and 121: 96 without double spiking. Geochimi
Page 122 and 123: 98 Geological Society of America, 2
Page 124 and 125: 100 Zamoruyev A., 1995a. Neotectoni
Page 126 and 127: 102 Ann. Rev. of Earth and Planetar
Page 128: 104 this work, especially all membe
Page 132 and 133: II Appendix A Tab. A1 Sample descri
Page 134 and 135: IV Tab. A2 continued Pamir frontal
Page 136 and 137: VI Tab. A2 continued Tertiary exten
Page 138 and 139: VIII Tab. A3 continued Sample Miner
Page 140 and 141: X Tab. A6 Rb/Sr and Sm/Nd isotopic
Page 142 and 143: XII Tab. A7 continued Apparent ages
Page 144 and 145: XIV Tab. A9 U/Pb isotopic ratios fr
Page 146 and 147: XVI Tab. A9 continued 207 Pb/ 206 P
Page 148 and 149: XVIII Tab. A9 continued 207 Pb/ 206
Page 150 and 151: XX Appendix B Plate B1 Cathodolumin
Page 152 and 153: XXII Plate B3 Cathodoluminescence i
Page 154 and 155: XXIV Plate B5 Cathodoluminescence i
Page 156 and 157: XXVI Tab. C2 Determination of the
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XXVIII
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XXX
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XXXII
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XXXIV
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XXXVI Tab. C5 continued Sample grai
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XXXVIII Tab. C5 continued Sample gr
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XL Tab. C5 continued Sample grain-n
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XLII Tab. C5 continued Sample grain
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XLIV
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XLVI Tab. C6 Zircon fission track a
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XLVIII
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LII
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LIV Tab. C7 Apatite and zircon fiss
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