Tracing the exhumation history of the Himalaya orogenic zone by detrital muscovite 40Ar/39Ar dating: implications for uplifting process of the Qinghai-Tibet Plateau, China

Systematic analysis of detrital muscovite 40Ar/39Ar data from the Himalayan foreland basin and Bengal fan stratigraphic units reveals the entire exhumation history of the Himalaya orogen since India-Asia plate collision event. The exhumation process was steady at the beginning, then increased up to the peak in around 22Ma with a rate of 4~5mm/a, subsequently, dropped dramatically and kept even ultimately with the rate of 2mm/a. The comparison of the exhumation histories between the edge of Tibetan Plateau and the Himalaya orogen could restrict the different reacting ways of the east and north boundaries of the Tibetan Plateau induced by India-Asia collision. The compression force was mainly absorbed in the first instance by large scale left-lateral strike-slip in the north edge of Tibetan Plateau till 30 Ma, which was followed by an important cooling and exhumation event triggered by the stagnancy of eastward movement of the Qaidam Block due to the countercheck of the North China Craton. Subsequently, with the continuous increasing of the cooling-exhumation rate in Himalaya and sustaining at a high level until 18 Ma and no marked exhumation event occurred either in north edge or east boundary, entire uplift and crust thickening of the Tibetan Plateau may occurred in this period. From late Miocene - early Pliocene to now, a series of pronounced uplift and exhumation events happened in the east edge resulted in large amounts landslides in conjunction with coeval river erosion, that means the compression force from the Himalaya was mainly absorbed by lateral growth and crust escaping of the Tibetan Plateau in the direction of east.