Crustal Accretion and Reworking within the Khanka Massif: Evidence from Hf Isotopes of Zircons in Phanerozoic Granitoids

Abstract

This paper presents a synthesis and analysis of geochronological, geochemical, and zircon Hf isotopic data of Phanerozoic granitoids within the Khanka massif, with the aim of revealing the accretion and reworking processes of continental crust within the massif. Zircon U-Pb dating indicates that Phanerozoic granitic magmatism within the Khanka massif can be subdivided into eight stages: Late Cambrian, Middle–Late Ordovician, Middle Silurian, Late Carboniferous, Early Permian, Middle–Late Permian to Early Triassic, Late Triassic–Early Jurassic, and Early Cretaceous. The zircon Hf isotopic compositions reveal that crustal accretionary events took place mainly in the Mesoproterozoic and Neoproterozoic. Through time, the zircon eHf(t) values gradually increase, indicating that the Phanerozoic granitic magmas were derived from the melting of progressively less ancient and more juvenile crust. The zircon eHf(t) values exhibit a gradual decrease with the increases in latitude, which implies that the amounts of ancient crustal components within the lower continental crust of the Khanka massif increased from south to north. At the same latitude range, the zircon Hf isotopic compositions also display some variations. We conclude, therefore, that significant horizontal and vertical heterogeneities existed in the lower continental crust of the Khanka massif during the Phanerozoic.