Neoarchean to Paleoproterozoic high-pressure mafic granulite from the Jiaodong Terrain, North China Craton: Petrology, zircon age determination and geological implications

摘要

The North China Craton is an ideal place for studying the transition of the Earth's thermal structure and tectonics at the Archean-Proterozoic boundary due to its good preservation of the similar to 2.5 Ga tectono-thermal events. We report the discovery of a high-pressure mafic granulite from the Jiaodong Terrain in the North China Craton. The mafic granulite occurs as garnet-clinopyroxene-orthopyroxene-hornblende gneiss enclaves within a late-Archean trondhjemite-tonalite-granodiorite (TTG) gneiss. Typical high-pressure mineral assemblage of garnet-clinopyroxene-plagioclase-quartz +/- rutile has been identified. Plagioclase + clinopyroxene +/- orthopyroxene +/- hornblende symplectite surrounding garnet ("white eye") is also observed. Using the conventional geothermobarometry and the pseudosection modeling, a clockwise metamorphic P-T path with the peak conditions at similar to 17 kbar and similar to 880 degrees C was determined. Zircon U-Pb analyses (SHRIMP) on the overgrowth rim of zircon grains of two samples from the same outcrop yielded a metamorphic age of 2473 +/- 6 Ma (MSWD = 0.8). The analyses on magmatic core gave a probable magmatic age of 2527 +/- 12 Ma (MSWD = 1.9). The high-pressure granulite facies metamorphism corresponds to a collisional event between the similar to 2.5 Ga crust and similar to 2.9 Ga crust at the dawn of Paleoproterozoic in the North China Craton. It also represents a new but rare case of a subduction-collision tectonics at the Archean-Proterozoic transition and provides insight into the change of the Earth's thermal structure. (C) 2014 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.