Structural development of the Lower Paleozoic belt of South China: Genesis of an intracontinental orogen

Abstract

An extensive structural study of Wuyishan and surrounding areas (South China) brings data on the structures formed prior to the Devonian unconformity, building the Lower Paleozoic belt. An Ordovician tectonic event was responsible for: (i) south-directed structures in the Wuyishan proper and its southern border, related to both thin and thick-skinned tectonics, accompanied by metamorphism and crustal thickening; (ii) north-directed structures to the west of Ganjiang Fault and north of Jiangshan–Shaoxing Fault, where only thin-skinned tectonics is visible. The southward deformation accommodating the shortening includes emplacement of thrust sheets, involving deep crustal material and some mantle peridotite, and likely repetition of continental material, both responsible for crustal thickening. The orogeny was due to the underthrusting of the southern part of the South China Block beneath the northern part of this block, closing the pre-existing Nanhua rift, created at around 850–800 Ma, and involving the rift sedimentary fill in the southward thrusting. The syn-metamorphic tectonic piling was followed by anatexis and granite emplacement at around 440–390 Ma. Our new U–Th–Pb EPMA monazite dating gives ages of 433 ± 9 Ma and 437 ± 5 Ma (Early Silurian) for the main anatectic event, and a younger age of 412 ± 5 Ma (Late Silurian–Early Devonian) for a late re-heating process. The Lower Paleozoic belt is an intracontinental orogen, without oceanic suture record. It shows some similarities with the Cenozoic European Pyrénées Chain, with a strong asymmetry.