Semi-adakitic magmatism of the Satkatbong diorite, South Korea: Geochemical implications for post-adakitic magmatism in southeastern Eurasia

Abstract

The Satkatbong diorite (190 Ma) and the older Yeongdeok granite (250 Ma) in the Yeongnam massif, which is part of the southeastern margin of the Eurasian plate, are affected by a subduction system that is associated with the Izanagi and Farallon plates. The Satkatbong diorite is characterized by its abundant mafic magmatic enclaves (MMEs), mantle affinity, and intermediate adakitic Sr/Y vs. Y signature, whereas the Yeongdeok granite is distinctly adakitic and felsic and contains few MMEs. These differences in adakitic features might be due to differences in the lithospheric mantle material and/or different mafic MME sources. The results of rare earth element (REE) analyses and newly proposed Sr/La modeling in this study indicate that these two plutons were both generated by slab-mantle mixing and continental assimilation, whereas the Satkatbong diorite was additionally affected by the injection of a mafic source of MMEs, which “diluted” its adakitic chemistry. The young and hot subducting ridge passing toward the northeast due to the oblique subduction of the Izanagi and Farallon plates during the Early Mesozoic could have given rise to slab melting and asthenospheric influence through slab melting regions and a slab window, respectively. This implies that the adakitic Yeongdeok granite produced by slab melting and then the semi-adakitic Satkatbong diorite produced by asthenospheric influence, including other similar adakitic to semi-adakitic magmatism, might have occurred along the areas affected by ridge subduction. We suggest that this sequential magmatism would be applicable for many continental arcs which experienced ridge subduction being one of the mechanisms of adakite to semi-adakite magmatism.