Constraining mixing and mingling processes from zoned magmatic enclaves: An example from the Taejongdae granite in Busan, Korea

Abstract

Zoned magmatic enclaves (MEs) within granitic intrusions provide valuable insights into the pre-intrusive processes involved in the formation of granitic magmas. This study focuses on the Taejongdae granite in Busan, Korea, which features uniquely zoned MEs, and aims to constrain the processes involved in their formation. Through a whole-rock geochemistry analysis, SHRIMP U-Pb zircon dating, and Lu-Hf isotope data, we investigated the geochemical characteristics and origin of the two magmas responsible for the zoned MEs (that is, dioritic and host granite magmas). Our findings have shown that the host granite aligns with the Bulguksa granites in the Gyeongsang Basin, which represent the I-Type magma resulting from the fractionation of magma generated through partial melting of the continental crust. In contrast, the dioritic magma exhibits a low K2O composition, high Sr content, and a positive-to-no Eu anomaly, indicating its formation via amphibole-dominated fractional crystallization under different pressure–temperature conditions. Both magmas share the same Cretaceous age and Hf ratios. The zoned MEs in the study area provide compelling evidence of magma mixing processes that occur between the outer dioritic zone and mafic core of the enclaves. However, the relationship between the outer dioritic zone and the host granite suggests limited interaction between the enclaves and host granite. This implies that mixing within the zoned enclaves occurred prior to enclosure in the host granite. By highlighting the significance of zoned magmatic enclaves, this case study advances our understanding of the pre-intrusive processes involved in the formation of granitic magmas, including magmatic mixing, mingling, and fractionation. These results offer important insights into the origin and geochemical characteristics of the two magmas and their interactions, thus contributing to a broader understanding of crustal evolution in subduction-related settings.