Petrogenesis and tectonic implications of Paleoproterozoic metapelitic rocks in the Archean Kongling Complex from the northern Yangtze Craton, South China

摘要

The Archean Kongling Complex in the northern Yangtze Craton is an ideal target to investigate the Precam-brian accretion and evolution of continental crust in South China. This study aims to unravel the crustal evolution and tectonic setting of the Yangtze Craton during the Paleoproterozoic time, using integrated studies of petrography, zircon U-Pb and Hf isotopes and whole-rock geochemistry of Paleoproterozoic metapelitic rocks in the Kongling Complex. Four representative metapelitic rocks contain garnet, and three of them include high-temperature metamorphic minerals as sillimanite or staurolite. Zircons from the metapelitic rocks show nebulous-sector zoning and rim-core microstructures, suggesting a metamorphic origin or a detrital origin with metamorphic overprints. The metamorphic zircon grains and metamorphic overgrowths have concordant (027)pb/(206) Pb ages at similar to 2.0 Ga, while detrital grains yield three distinct age populations of >2.5 Ga, 2.4-2.2 Ga and 2.2-2.1 Ga. The age patterns indicate that the depositional age of the metasedimentary rocks was 2.1-2.0 Ga. Arc-related magma production represented by the Houhe gneiss in the northern part of the craton could be the source of the 2.2-2.1 Ga inherited zircons, because of the similarities of whole-rock geochemical compositions and zircon U-Pb-Hf isotopic signatures between the investigated metapelitic rocks and the gneiss. The 2.4-2.2 Ga zircons have Hf model ages (T-DM2) of similar to 3.5-2.6 Ga, and the >2.5 Ga zircons have T-DM2 ages varying from 3.3 Ga to 2.9 Ga. Our data support previous knowledge that there were three episodes of growth and reworking events of the Archean Yangtze continental crust, ca. 3.3-3.2 Ga, 2.9 Ga, 2.7-2.6 Ga, and show that the Yangtze Craton has experienced Paleoproterozoic reworking during 2.4-2.2 Ga and the growth and reworking during 2.2-2.1 Ga.