Abstract:

Longchuan Basin is a continental Tertiary microbasin developed on Cambrian metomorphic basement. The deposits are mainly coarse fluviolacustrine debris. In the basin, colluvial fan, alluvial fan and fan delta are well developed.The basin can be divided into uplift-overlap belt in the southwest, fault-depression belt in the central part, fault-block belt in the mid-western part and slope overlap belt in the northwest.The Longchuan I3asin is a half-grabed controlled by comtemporaneous boundary faults formed by crest collapse. It is considered that the basin is a pull-apart and strike-slip basin resulted from multi effects through pull-apart action in the early stage, tenso-shearing in the middle stage and superimposition in the late stage under dexdral tenso-shearing mechanics. The evolution of the basin underwent rapidly faulted depression in the early stage, stable development in the middle stage and shrivelling in the late stage. In some extent, this mode can be used to explain the formation mechanism of many Tertiary microbasins in the westward of the Nujiang River in Yunnan Province.