Tectonic Evolution of the Middle Frontal Area of the Longmen Mountain Thrust Belt,Western Sichuan Basin,China

By analyzing the balanced cross sections and subsidence history of the Longmen Mountain thrust belt,China,we concluded that it had experienced five tectonic stages:(1) the formation stage (Tx) of the miniature of Longmen Mountain,early Indosinian movement,and Anxian tectonic movement created the Longmen Mountain;(2) the stable tectonic stage (J) where weaker tectonic movement resulted in the Longmen Mountain thrust belt being slightly uplifted and slightly subsiding the foreland basin;(3) the intense tectonic stage (J),namely the early Yanshan movement;(4) continuous tectonic movement (K-E),namely the late Yanshan movement and early Himalayan movement;and (5) the formation of Longmen Mountain (N-Q),namely the late Himalayan movement. During those tectonic deformation stages,the Anxian movement and Himalayan movement played important roles in the Longmen Mountain’s formation.The Himalayan movement affected Longmen Mountain the most;the strata thrust intensively and were eroded severely.There are some klippes in the middle part of the Longmen Mountain thrust belt because a few nappes were pushed southeastward in later tectonic deformation.