A cold shrink model for the NS-trending rifts in the Himalaya orogenic zone

The NS-trending rifts perpendicular to the Himalaya orogenic zone have long been interpretated as the structural features of the E-W extension of the Qinghai-Xizang Plateau. Now it should be challenged by modern global positioning system (GPS) data from recent studies, for that the eastward and westward movements of the crust are scarce or zero in this zone. Referenced to the previous data, the orogenic precesses may be discriminated two eposides:hot mountain building (25-13 Ma) and post-orogenic cooling (< 13 Ma). The Himalaya orogenic zone is characterized by thermal expansion and outward-growth of the crustal materials in the first eposide. The Great Himalaya Crystalline (GHC) was extruded and gave rise to the faulting of major faults such as the Main Central Thrust (MCT), South Tibet Detachment (STD) and Great Counter Thrust (GCT). The northward subduction rates of the Indian plate dropped down to the lowest levels, i. e., about 45 mm/yr. After mountain building, the cold shrink happened in the second eposide. The pre-existing tectonic-thermal activities were gradually weakened or ceased, and the northward convergence rates of Indian plate speed up again to 50 mm/yr. It is suggested that the NS-trending rifts may be related to the post-orogenic cooling events, and result from the EW-trending cold shrink of the Great Himalaya Crystalline and leucogranites within the limit of eastern and western Himalaya syntaxis. A cold shrink model for the origin of the NS-trending rifts is introduced in this paper, by which the throw of normal faults in rift margins was calculated.