Abstract:

Qaidam Basin began to develop after Indosinian movement.During the Jurassic-Eocene,the basin was small,confined within mountain fronts,and in the Oligocene-Miocene,the whole basin subsided,thus formed a huge depression.In the Pliocene-Quaternary,it uplifted and folded slowly.It is clear that the main period of subsiding and folding of the basin was generally synchronized with the intense uplifting of Qinghai-Tibet Plateau.originated with the northward compression of India Plate.The basin's evolution process has revealed itself in a roughly N-S compression stress field.The strong compression force and increasingly depositing load resulted in a variation of lithofacies in the lower part of the earth's crust,i.e.,rock density becomes heavier and heavier,then the crust began to sank and formed a huge depression basin.The uplift of the basin in its late evolution may relate to the expansion of the former rocks which changed from eclogite into gabbronitc resulted from the exothermic reaction of radioele-ments under the huge sedimental cover.The folds and overthrusts were formed appearently due to continuous compression.It is shown by crusta depth measurement that a abnormal velocity layer of 7.8km/sec of P wave can be found within the basin which is between the crust and the mantle.This may be the resuIt of lithofacies variation.