The Karst of Tibet and Other Parts of Chinese Central Asia
These areas of mainly high-altitude karst occur in the western half of China, west of the Hengduan-Longmen-Luipan-Helan mountains line (see Sect. 1.1 and Figs. 4 and 61). It is almost half the total area of China. Limestones occur over much of this western tectonic megaregion, particularly in Tibet, where about one-fifth of the terrain is karstic (Fig. 1). All this vast area is arid, with an aridity index of one or more (Yuan Daoxian et al. 1991), and with an annual average rainfall of 100–400 mm and in parts like the Tarim basin (Tali-mu) only 20–25 mm. The average annual temperature is about 2–6 °C outside the basins and 8-10 °C inside them (Yuan Daoxian et al., 1991, p. 110), but the climate is still strongly seasonal. The area includes Xinjiang, Qinghai, Inner Mongolia, Gansu and Tibet and stretches from the Himalayas in the south to Lake Baikal in the north. It is a zone of north-south compressional deforma tion stretching from the Himalayas to Baikal (Molnar and Deng cited in Dewey et al. 1988). Within this zone of deformation are rigid regions such as the Tarim and Qaidam basins (Fig. 61). The tectonic evolution of the high Tibet plateau was discussed by Dewey et al. (1988). They argue that a thick underthrust of the Indian Shield does not underlie Tibet as often thought, and discuss alternative views. They contend that rapid lithospheric thinning by deformation or stoping would account for the very rapid and recent uplift of the Tibetan plateau, its widespread recent volcanism, its hot springs and E-W extension (Dewey, et al. 1988). “The Indian lithosphere may be thought of as an indenting buttress with a thinner Northern edge generated by Neotethyan Triassic/Jurassic rifting, which collapsed to form the Himalayan Zone of shortening” (Dewey et al. 1988).
KeywordsClay Depression Uranium Calcite Cretaceous
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