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62 Palaeogene volcanic rocks of central and southern Tibet show arc affinities (Coulon et al. 1986) and Ar/Ar ages ranging between 110 and 80 Ma in the north and between 60 to 50 Ma in the south. Coulon et al. (1986) relate this ages to north directed subduction beneath Lhasa, with shallow subduction until 80 Ma, followed by steeper subduction. The plutonic Gangdese/Transhimalaya belt of the southern margin of Lhasa is the manifestation of this subduction zone (e.g. Schärer et al. 1984, Harris et al. 1988, Miller et al. 2000). Miller et al. (2000) compared several own and published age data of magmatic rocks from different parts of the whole Transhimalayan magmatic belt and could define two major intervals of calc-alkaline magmatism: a mid-Cretaceous peak at about 120-90 Ma and a Palaeocene and Eocene time interval at around 60 to 40 Ma. The first interval fits very well the findings of this study, even so in the Pamirs it is concluded that the Cretaceous magmatism may have been bimodal with peaks at ~120 Ma and ~75 Ma. The amalgamaltion history beween the Indus –Yarlung and the Rushan Pshart sutures is in many aspects speculative (e.g. Hildebrand et al. 2000, Fraser et al. 2001). South of the southern Pamirs and Lhasa follow the Wakhan, eastern Hindu Kush, and Karakoram blocks. Whereas the South Pamirs comprises mainly undifferentiated Cretaceous and Tertiary intrusives, the Karakorum is composed of metamorphic and sedimentary rocks intruded by subduction related granitoids with predominately Early Cretaceous and locally Jurassic ages. The boundary between the East Hindu Kush block and the Karakorum is supposed along the Rich Gol Metamorphic Complex (RGMC), a narrow strip along the Tirich Mir fault (Zanchi et al. 1997). The RGMC is composed of highgrade metabasites with serpentinites and metapelites. Zanchi et al. (1997) conclude, that the East Hindu Kush and Karakorum share a common history at least since Mid- Cretaceous, as both blocks are intruded by the East Hindu Kush granitoids. One of these, the Tirich Mir pluton, records a Rb/Sr whole rock age of 115±4 Ma (Desio et al. 1964), but is probably poorly constrained (Hildebrand et al. 2000). The Kafiristan pluton yield a Rb/Sr whole rock age of 480 Ma (Debon et al. 1987), which is a typical Gondwanan age. Within the Tirich Mir fault, pegmatite dikes crosscut staurolith schists; the latter yield U-Pb monazite ages of 135-126 Ma near Gharam Chasma. U-Pb dating of uraninites from one of these pegmatites revealed an age of 114±2 Ma (Hildebrand et al. 2001). Thrusting along the Tirich Mir fault took place during the Cretaceous (Hildebrand 1998). The southern margin of the eastern Hindu Kush region was discriminated by a continental margin type above a north-dipping Tethyan oceanic subduction zone. The collision between the Karakorum and the southerly adjacent Kohistan-Ladakh arc was about ~80 Ma along the Shyok/Northern suture (e.g. Chandra et al. 1999). Finally, India collided with the amalgamated Eurasia at about 55- 50 Ma. A major phase of crustal continental melting in the South Pamirs, East Hindu Kush, and Karakorum regions led to the emplacement of leucogranites, like the Gharm Chasma pluton (~24 Ma) in the Hindu Kush and the Baltoro granite in the central and eastern Karakorum (Hildebrand et al. 2001). Zircon geochronology of Cretaceous and Cenozoic granitoids from the southern Qiangtang to northern South Pamirs and from crustal xenoliths erupted from 90-100 km depth in the south-eastern Pamirs during the Miocene (Ducea et al. 2003) chronicles multiple Phanerozoic additions to a Proterozoic crust derived from Gondwana. The
most distinct magmatic events occured during the Cambro-Ordovician (575-410 Ma; Qiangtang and South Pamirs), Triassic (250-200 Ma; Qiangtang, by southward subduction along the Tanymas/Jinsha suture), Mid-Jurassic (200-150 Ma; Qiangtang and Rushan Pshart zone, by northward subduction along the Rushan Pshart/Bangong- Nujiang suture), Mid-Cretaceous (~120 Ma; Qiangtang, Rushan Pshart, and South Pamirs, by probably northward subduction along the Tirich Mir/Kilik (?)suture), and Late Cretaceous (~80 Ma; Qiangtang, Rushan Pshart, and South Pamirs, by subduction along the Shyok suture). 63
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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
Page 36 and 37: 12 Geochemisches Zentrallabor, Univ
Page 38 and 39: 14 mean UO+/U+ and Pb+/U+ value. Si
Page 40 and 41: 16 apatites and zircons were counte
Page 42 and 43: 18 number of simulation runs and th
Page 45 and 46: Two Palaeozoic sutures divide the C
Page 47 and 48: igneous and sedimentary rock sequen
Page 49 and 50: Triassic and the formation of an is
Page 51 and 52: 27 Lake Karakul The Lake Karakul ar
Page 53: 3.3.2 Major and trace elements Majo
Page 56 and 57: 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 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 108 and 109: 84 south to 18 Ma in the north; 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
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VI Tab. A2 continued Tertiary exten
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VIII Tab. A3 continued Sample Miner
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X Tab. A6 Rb/Sr and Sm/Nd isotopic
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XII Tab. A7 continued Apparent ages
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XIV Tab. A9 U/Pb isotopic ratios fr
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XVI Tab. A9 continued 207 Pb/ 206 P
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XVIII Tab. A9 continued 207 Pb/ 206
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XX Appendix B Plate B1 Cathodolumin
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XXII Plate B3 Cathodoluminescence i
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XXIV Plate B5 Cathodoluminescence i
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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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