Mesozoic intracontinental ductile shearing along the Paleozoic Shangdan suture in the Qinling Orogen: Constraints from deformation fabrics and geochronology

Abstract The Qinling Orogen, located between the North and South China Blocks, records subduction-collisional orogeny along Paleozoic Shangdan Triassic Mianlue sutures, Mesozoic intracontinental orogenesis, which all played an important role in building present tectonic framework topography. strike-slip Shagou ductile shear zone that overprints suture Belts is crucial for understanding deformation Orogen. microstructures, asymmetrical fabrics, kinematic vorticities (0.81–0.95) suggest sinistral simple shear. quartz c-axis patterns from felsic mylonites exhibit Y-maximum indicating activity of prism <a> slip, while those amphibole-rich display both Z-maximum fabrics showing combined basal slip systems. In mafic mylonites, plagioclase were induced by (010)[100] (001)[100] systems, amphibole probably related to anisotropic growth or passive rotation rigid clasts. Equilibrium P–T conditions 4.28–6.12 kbar 646–727 °C estimated geothermobarometry main occurred under amphibolite facies at middle–lower crustal depths. Zircon U-Pb ages constrain their protolith rocks have crystallized 816 ± 25 Ma 726–718 Ma, intense mylonitization shearing ca. 200–187 Ma. A U–Pb zircon age 132 3 a granitic dike cutting foliation 40Ar/39Ar plateau 119.0 0.9 together evolved through decompression exhumation stages time period 132–119