Triassic polyphase deformation in the Feidong-Zhangbaling Massif (eastern China) and its place in the collision between the North China and South China blocks

Abstract

The Feidong-Zhangbaling Massif is located between the Dabieshan and Sulu areas along the Tan-Lu fault in eastern China. Five tectonic-metamorphic events are distinguished there. The earliest deformation (D1) corresponds to a southward compression that occurred during subduction of the South China Block below the North China Block. Top-to-the-south shearing is coeval with 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 deformational phase of exhumation (D3) which is distinct from the main event (D2). Previous 40Ar– 39Ar mica dates ranging between 245 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 presented along the Tan-Lu fault suggests that it did not play a significant role in the exhumation of high-pressure metamorphic rocks.