Two phases of Paleoproterozoic metamorphism in the Zhujiafang ductile shear zone of the Hengshan Complex: Insights into the tectonic evolution of the North China Craton

摘要: Abstract The Zhujiafang ductile shear zone is located in the central Hengshan Complex, a key area for understanding Paleoproterozoic tectonic evolution of Trans-North China Orogen, North Craton. Detailed metamorphic and geochronological analyses were carried out on metapelite garnet amphibolite from zone. preserves two phases mineral assemblages: early kyanite-rutile-bearing assemblage late chlorite-staurolite-bearing garnet–mica schist, inclusion-type muscovite (high-Si) + kyanite sillimanite-bearing sillimanite–mica gneiss. Garnet occasionally exhibits pronounced two-stage zoning characteristic diffusion core with irregular pyrope (Xpy) grossular (Xgr) contents growth rim Xpy Xgr increasing outwards. isopleths maximum Si content P–T pseudosections suggest that assemblages underwent medium-high-pressure type metamorphism pressures up to 12–14 kbar at 700–750 °C. predict separated clockwise path peak conditions 6.5 ± 0.2 kbar/620 ± 10 °C (medium-low-pressure type). mainly composed garnet, hornblende, plagioclase, ilmenite quartz, without overprinting except localized corona textures. Phase modeling suggests rock has experienced high-amphibolite facies 10.5 ± 0.8 kbar/770 ± 50 °C, which broadly consistent early-phase metapelite. Zircon U Pb dating yields age groups 1.96–1.92 Ga 1.87–1.86 Ga are interpreted represent timing metamorphism. Two orogenic events may have occurred respectively ~1.95 Ga ~1.85 Ga Hengshan–Wutai area. older phase orogeny was resulted continental collision younger be caused by within-plate deformation. final exhumation high-grade rocks formed (i.e. 1.95 Ga) should related deformation/metamorphic event.