ON THE MECHANISM OF A NEW TYPE OF INTRACONTINENTAL SUBDUCTION——THE LONGMENSHAN SUBDUCTION

The Longmcnshan Thrust Belt is one of the typical thrust belts in China.Based on the detail studies of the lithosphere structures in the Longmenshan Region and the structural environment previous to the formation of the thrust belt,and combined with the geophysical and earthquake informations,the authors of this Paper suggested that the Longmenshan Thrust Belt developed under the mechanism of intracontinental subduction is resulted from the adjustment of deep-seated matter which made the lithosphere of the Sichuan Basin subducting to the Longmenshan and the western plateau of Sichuan.The thrusting movements took place along multiple plastic layers within the lithosphere (the upper part of the mantle,the lower,middle and upper crustal layers) during polystages (the latest of the Indosinian,the Yashanian,the Himalayan periods).The type of the subduction model is quite different both from B-subduction and A-subduction,and it is named as the type of the Longmenshan Subduction,abbreviated to the L-subduction.On the basis of the studies mentioned above,the geological conditions of oil/gas are elucidated in the paper for the Longmenshan Region.