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OROGENIC BELTS 307
65°E 70°E 75°E 80°E 85°E 90°E 95°E 100°E 105°E
45°N 45°N
Tien Shan Eurasia
Fault
North China
Talas Ferghana
Alashan
40°N 40°N
Tarim Basin
Helmand
Pamir Altyn Tagh Fault Qaidam Qilian Shan
AKMS Basin
Kunlun Fault
WS
35°N Herat Fault MMT Karakorum Fault JS 35°N
Songpan-Ganzi
Tibetan Plateau Qiangtang Xianshuihe
Quetta Chaman Lhasa BNS Fault Longmen Sichuan
Jiali Fault
30°N Fault Himalaya IZS ES Basin 30°N
South
Main Boundary Thrust
25°N India China 25°N
suture
thrust fault
normal fault 35 - 50 mm a -1 Indochina Red River Fault
20°N strike-slip fault 20°N
65°E 70°E 75°E 80°E 85°E 90°E 95°E 100°E 105°E
Figure 10.13 Shaded relief map showing major faults and topographic features of the Himalayan–Tibetan orogen.
Fault traces are from Hodges (2000), Yin & Harrison (2000), Tapponnier et al. (2001). WS, Western Himalayan Syntaxis;
ES, Eastern Himalayan Syntaxis; MMT, Main Mantle Thrust; AKMS, Ayimaqin–Kunlun–Mutztagh suture; JS, Jinsha suture;
BNS, Bangong–Nujiang suture; IZS, Indus–Zangbo suture. Map was constructed using the same topographic data and
methods as in Fig. 7.1.
anomalies in the Indian Ocean and paleomagnetic lution of the India–Eurasia collision. Gaetani & Gar-
measurements from the Ninety-East Ridge and the zanti (1991) showed that marine sedimentation stopped
Indian subcontinent record the northerly drift of the and terrestrial deposition along the southern margin of
Indian plate and allow the reconstruction of its paleo- Asia commenced at 55–50 Ma, which is in accord with
latitude (Fig. 10.14). The data show a rapid decrease interpretations of the age of the initial collision derived
in the relative velocity between the Indian and Eurasian from magnetic anomalies. However, this observation in
plates at 55–50 Ma. This time interval commonly is fact only constrains the youngest possible age of the
interpreted to indicate the beginning of the India– onset of the collision because as much as 500–1000 km
Eurasia collision. However, it is uncertain whether the of the Indian passive continental margin has been
decrease resulted from an increase in the resistance to underthrust beneath Asia, potentially eliminating the
continued motion of the India plate as it collided with early record of the collision (Yin & Harrison, 2000).
Eurasia or if it simply reflects a sudden decrease in Beck et al. (1995) showed that trench and forearc mate-
spreading rate along the mid-oceanic ridge south of rial along the southern margin of the Eurasian plate
India. This latter possibility allows the age of the initial near Pakistan was thrust onto the northern edge of
contact between India and Eurasia to be older than India after 66 Ma and before 55 Ma. Willems et al. (1996)
55–50 Ma. found changes in sedimentary facies and depositional
Stratigraphic and sedimentological data provide patterns in south-central Tibet that suggest initial
additional information on the age and progressive evo- contact between some parts of India and Asia could