Crustal evolution of northeastern Yeongnam Massif, Korea, revealed by SHRIMP U–Pb zircon geochronology and geochemistry

Abstract

Paleoproterozoic igneous activity and metamorphism are widespread in North China and Korean Peninsula. As a part of a Precambrian tectonic unit located in the southeastern margin of Korea, the northeastern Yeongnam Massif consists mainly of metasedimentary rocks and granitoids such as the Buncheon granite gneiss, Hongjesa granite and leucogranite. Here we present their SHRIMP zircon U–Pb ages and geochemical compositions. Magmatic oscillatory zones of zircon grains from the Buncheon granite gneiss yielded a concordia age of 1990±5Ma. The detrital zircon analyses of metasedimentary rocks tightly constrain the depositional age between 2.02Ga and 2.00Ga. Subsequently the igneous and detrital zircons were overgrown during a metamorphic overprint at ca. 1.95Ga. Dark-cathodoluminescent, metamorphic rims of zircon grains from the metasedimentary rocks and Buncheon granite gneiss are dated at 1.89 to 1.84Ga, which is contemporaneous with the emplacement age of leucogranite. All granitoids are peraluminous and show distinct Eu negative anomalies. Also, the initial whole-rock εNd values of the granitoids are consistently negative. Such geochemical features are indicative of recycled crustal source rocks with residual plagioclase. The granitoids are enriched in large-ion-lithophile elements and depleted in high-field-strength elements in their normalized trace element patterns, which is typical of subduction zone magmas. Our compilation of the literature shows that the Yeongnam Massif lacks late Archean and Neoproterozoic igneous or metamorphic phases which are well recorded in the other two Precambrian massifs in Korea, namely the Gyeonggi and Nangrim Massifs. All three massifs, however, show a strong metamorphic imprint at ca. 1.85Ga, possibly associated with the formation of the supercontinent Columbia. There remain ambiguities on the correlation between Korean and Chinese Precambrian tectonic units, considering discrepancies in the geochronological framework of magmatism and metamorphism.