Page 324 - Global Tectonics
P. 324

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
   319   320   321   322   323   324   325   326   327   328   329