Triassic poplyphase deformation in the Feidong-Zhangbaling massif (Eastern China) and its place in the collision between the North China and South China blocks.
Abstract
In eastern China, the Feidong-Zhangbaling Massif is located between the Dabieshan and Sulu areas along the Tan-Lu fault. Five tectonic-metamorphic events are distinguished there. The earliest deformation (D1), corresponding to a southward compression occurred during the subduction of the South China Block below the North China Block. Top-to-the-south shearing is coeval with the Late Permian-Early Triassic blueschist facies metamorphism, and possibly with the development of south-verging recumbent folds in the Neoproterozoic-Paleozoic sedimentary cover of the South China foreland. The main ductile deformation (D2) is an extensional one, characterized by top-to-the-north shearing, coeval with the early stage of exhumation of the high-pressure rocks. A top-to-the-NW ductile shearing, and microfolds overturned to the northwest belong to a second deformation phase of exhumation (D3) which is distinct from the main event (D2). Previous 40Ar-39Ar mica dates ranging between 245 Ma and 212 Ma suggest Late Permian-Early Triassic ages for the D1 to D3 events. The D4 event produced NE-SW trending folds in the sedimentary cover interpreted as gravity collapse structures. A Late Cretaceous brittle extensional event (D5) controls the opening and infill of continental half-grabens. In the study area, the Tan-Lu fault is a Cretaceous brittle normal fault. The lack of ductile deformation along the Tan-Lu fault cannot account for the exhumation of high-pressure metamorphic rocks.