Petrogenesis of paleoproterozoic (2.02-1.96 Ga) metagranitoids in the southwestern Yeongnam Massif, Korean Peninsula, and their significance for the tectonic history of northeast Asia: Insights from zircon U-Pb-Hf isotope and whole-rock geochemical compositions

摘要

The Jangsu-Gokseong area is located in the southwestern part of the Yeongnam Massif and mainly consists of Precambrian metagranitoids (metagranite, metaleucogranite and metagranodiorite) with minor migmatite and marble. Sensitive high-resolution ion microprobe (SHRIMP) zircon U-Pb dating shows that the metagranitoids emplaced during ca. 2.02-1.96 Ga and metamorphosed at ca. 1.89-1.87 Ga. The metagranitoids show calc-alkaline trends, enrichment in large lithophile elements and negative Nb and Ta anomalies with low Sr/Y (< 12), Nb/Th (< 1) and Nb/Zr (< 0.1) ratios. The metagranitoids have negative epsilon(Hf)(t) values (-1.63 to -6.41) with a Paleoarchean two-stage model age (T-DM2 = 3.25 Ga). These data suggest that the protoliths of the metagranitoids were derived from ancient crustal materials with metagraywacke or metatonalitic compositions and formed in a subduction-related setting. The intrusion ages and geochemical composition of the metagranitoids in the study area match well with those of Paleoproterozoic metagranitoids distributed along the northern margin of the central to northeastern Yeongnam Massif. These metagranitoids show that Paleoproterozoic (ca. 2.02-1.96 Ga) subduction-related magmatism occurred widely along the northern margin of the Yeongnam Massif, which has not been reported from the Gyeonggi and Nangrim massifs on the Korean Peninsula and the Jiao-Liao-Ji belt in the eastern North China Craton. Therefore, the Yeongnam Massif might have existed as a separate crustal unit at least during the Paleoproterozoic.