Carboniferous–Triassic subduction in the Qinling orogen

Abstract

The Qinling–Tongbai–Hong’an–Dabie–Sulu Orogen links two cratons, North China and South China, and records the reorganization and transfer of plates from Rodinia to Gondwana and Eurasia. The formation of North Qinling at the southern North China margin (524–378 Ma) by subduction–accretion processes and the collision between North and South China (270–190 Ma) are pivotal for this reorganization. We outline the geological processes that link both events by combining phase equilibria modeling, conventional thermobarometry, U–Pb (zircon, titanite, garnet–staurolite) and ⁴⁰Ar/³⁹Ar and Rb–Sr (amphibole, micas) geochronology. The North Qinling experienced transpressional reactivation of shear zones, local fluid percolation, and metamorphism up to the lowest amphibolite facies (≲ 550 °C) until 324 Ma; protracted uplift and erosion with slow cooling (1 °C/Myr) led to its peneplanation prior to 260 Ma. The southerly abutting Wuguan Complex underwent two consecutive metamorphic events: while the older was diverse (600–750 °C, 0.5–1.2 GPa), the younger had a regionally homogeneous peak (590 °C, 0.9 GPa) at c. 324 Ma. Subduction and early exhumation of the South China margin occurred at 299–250 Ma in East Qinling. During the exhumation, medium-grade blueschists (500 °C, 1.0–1.3 GPa) were imbricated with low-grade rocks (300 °C, 0.5–1.0 GPa). Subsequent extensional doming with percolation of a low-salinity, hydrous fluid and south-vergent thrusting brought these rocks to near-surface levels by 200 Ma. New and published data indicate that plate convergence governed geologic processes to the south of North China not only before 378 Ma but protractedly or episodically until 190 Ma. This prolonged history is inconsistent with the amalgamation of North China to Gondwana but substantiates paleogeographic reconstructions with North China as a Paleozoic island continent. Carboniferous–Triassic subduction in the Qinling ultimately led to the welding of North China and South China, completing their transfer from Rodinia to Eurasia.