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44 A granite pebble from a ?Miocene conglomerate in the Pshart valley (96P4e) gave a Late Jurassic 40 Ar/ 39 Ar age of 151.4 ± 1.7 Ma (Fig. 3.9k). 40 Ar/ 39 Ar dating of muscovite from a basement rock north of Murgab (A96M18h) yielded an age of 166.2 ± 0.5 Ma (Fig. 3.9l). Cretaceous intrusions of the Central Pamirs and RPZ gave late Early Cretaceous 40 Ar/ 39 Ar cooling ages of ~105 and ~101 Ma (samples M96M7 and P7, respectively; Fig. 3.9m,n) and 40 Ar/ 39 Ar cooling ages from two intrusions of the northernmost South Pamirs spread from ~98 Ma (P2) to ~70 Ma (P5) (Fig. 3.9o,p). 3.5 Sr and Nd isotope compositions of the granitoids Correlated isotopic compositions of the Sm/Nd and Rb/Sr systems have been used to obtain information about the magma sources and to determine crustal formation ages. Twelve igneous samples have been analysed (Appendix A, Tab. A6) from the Northern and Central Pamirs and the Rushan Pshart Zone. In general, model ages assess the time at which a rock separated from its mantle source region. For igneous and meta-igneous rocks this is a good estimate of the crust formation age. Most of the Pamiran granitoids were derived by the melting of older continental crust (S-type granites). Therefore model ages will be indicative of the age of the crustal source. This is possible because the intracrustal fractionation process does not greatly disturb the Sm/Nd ratio of the source. Often, however, granites are a mixture of crustal and mantle sources. When this is the case, calculated model ages may give very misleading results (Arndt & Goldstein 1987). In this study, model ages were calculated with the equation of Liew & Hofmann (1988) with a two component reservoir of continental crust (CC) and depleted mantle (DM). Initial Sr-ratios are lowest for the Carboniferous metavolcanic rocks of the Northern Pamirs (Altyndara valley) with ( 87 Sr/ 86 Sr) i = 0.705264 to 0.705642 and for the Triassic leucogabbro (( 87 Sr/ 86 Sr) i = 0.705311). All other Sr-initials from Triassic/Jurassic granitoids range from 0.706974 to 0.709310, indicating crustal contamination. The Cretaceous granitoids have initial Sr-ratios between 0.709745 and 0.711105, implying even more crustal involvement. Such increasing contribution of crustal material in Cretaceous granites correlates with the low initial Nd-values of 0.512001 to 0.511820. The highest ( 143 Nd/ 144 Nd) i values obtained the metavolcanic rocks from the Altyndara valley, which range from 0.512191 to 0.512508. The leucogabbro shows also a high ( 143 Nd/ 144 Nd) i value of 0.512477, whereas the rocks of the Lake Karakul batholith fall into a very narrow range between 0.512148 and 0.512159. The Triassic/Jurassic samples have slightly lower values around 0.512050. Cretaceous granites show the lowest ( 143 Nd/ 144 Nd) i values . The �Nd (0) values of the Cretaceous granites fall within the range of -11 to -12, those of the Triassic/Jurassic granitoids of the Central Pamirs and Rushan Pshart zone around -8 with the exception of the leucogabbro with an �Nd (0) value of - 0.3. �Nd (0) values of the Karakul lake batholith are -6 to -7. The metavolcanic rocks show a wider spread of �Nd (0) values from +4.5 to -3.4. Model ages for these rocks mirror this variety with ages increasing from 0.6 Ga for the southern samples to 1.1 Ga for the northern samples. The model ages of the Lake Karakul batholith are about 1.3 Ga, whereas the Triassic/Jurassic plutons are very consistent in the range of 1.4 Ga.
45 The Cretaceous plutons show model ages of around 1.7 Ga. Two outliners are represented by a much younger model age of 0.7 Ga for the leucogabbro, and by the oldest model age of around 2.0 Ga of sample P2, a Cretaceous granite. This granite has a very high 147 Sm/ 144 Nd-ratio, implying a high degree of fractionation, due to the likely presence of garnet in the magma source. From Fig. 3.10c one can conclude a source region for the gabbro bodies of the north-eastern part of the Murgab dome (sample 96M9a) close to the standard reference reservoir which has �Nd (0) and �Sr (0) values of 0. In a similar range are the metavolcanic rocks from the Altyndara valley. The amount of crustal contamination increases from the upper left to the lower right. DePaolo & Wasserburg (1979) pointed out that mixing of two magma sources, respectively the contamination with crustal material, would create mixing relations dominated by a large variation of �Sr (0) values with relatively stable �Nd (0) values. This is also obvious from Fig. 3.10c: the Cretaceous samples show a range of �Sr (0) values from ~100 to ~350 with �Nd (0) values of about -11 to -12. Triassic and Jurassic rock samples from the Lake Karakul and Rushan Pshart zone show �Nd (0) values of about -6 to - 8 and the �Sr (0) values spread from ~150 to ~200. The Karakul batholith seem to have a higher amount of mantle component or less crustal contamination than the other Triassic/Jurassic samples from the Rushan Pshart zone and the Cretaceous samples.
Page 1:
Institut für Geowissenschaften (IF
Page 4 and 5:
Key words: Tien Shan, Pamirs, Tibet
Page 6 and 7:
* Nr. 22 MESCHEDE, M. (1994): Tecto
Page 8 and 9:
* Nr. 55 REINECKER, J. (2000): Stre
Page 13 and 14:
The amalgamation of the Pamirs and
Page 15: Wer aber je auf Asiens Erdboden sch
Page 20 and 21: viii (1971). Black lines with arrow
Page 22 and 23: x sample locations and age distribu
Page 24 and 25: xii Swedish expeditions followed. I
Page 26 and 27: 2 postulated that the Safed Khers a
Page 28 and 29: 4 Zusammenfassung Die paläozoische
Page 30 and 31: 6 (d) Oberkreide Spaltspurenalter w
Page 32 and 33: 8 deformation propagate from the pl
Page 34 and 35: 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 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 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
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104 this work, especially all membe
Page 132 and 133:
II Appendix A Tab. A1 Sample descri
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IV Tab. A2 continued Pamir frontal
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VI Tab. A2 continued Tertiary exten
Page 138 and 139:
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
Page 146 and 147:
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
Page 158 and 159:
XXVIII
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XXX
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XXXII
Page 164 and 165:
XXXIV
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XXXVI Tab. C5 continued Sample grai
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XXXVIII Tab. C5 continued Sample gr
Page 170 and 171:
XL Tab. C5 continued Sample grain-n
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XLII Tab. C5 continued Sample grain
Page 174 and 175:
XLIV
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XLVI Tab. C6 Zircon fission track a
Page 178 and 179:
XLVIII
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LII
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LIV Tab. C7 Apatite and zircon fiss
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