Metamorphic evolution and 40Ar/39Ar geochronology of the Wuguan complex, eastern Qinling area, China: Implications for the late Paleozoic tectonic evolution of the Qinling orogen

Abstract

The late Paleozoic tectonic evolution of the Qinling orogen is poorly constrained. The Wuguan Complex, which lies between the North Qinling and South Qinling tectonic belts, represents a late Paleozoic metamorphic belt of the Qinling orogen. In this contribution, we report new metamorphic pressure–temperature (P–T) constraints and 40Ar/39Ar ages of garnet amphibolites and garnet-bearing metapelites from the Wuguan Complex. Textural observations and mineral compositions, especially garnets with two stages of growth, indicate the Wuguan Complex experienced two distinct metamorphic events. Conventional geothermobarometry and phase equilibria modelling indicate that the earlier metamorphism had peak P–T conditions of 660–725 °C and 8.0–12.0 kbar with a clockwise P–T path, whereas the later metamorphic overprint records P–T conditions of 560–610 °C and 7.5–9.0 kbar. Hornblendes from amphibolites yield 40Ar/39Ar ages of ~306–299 Ma, whereas muscovites from garnet-bearing metapelites yield 40Ar/39Ar ages of ~252–251 Ma. The two groups of 40Ar/39Ar ages correspond to the cooling time of the two distinct metamorphic events, respectively. Combining with previously published zircon UPb ages from the Wuguan Complex and two groups of metamorphic ages from the Guishan Complex and the Xiongdian eclogite belt, we infer that the earlier metamorphism probably occurred at the hangingwall of a subduction zone during Carboniferous subduction of oceanic crust. The later metamorphic overprint might have been related to the initial collision between the Sino-Korean and Yangtze cratons during the late Permain.