R6: Plutonic rocks, volcanic rocks and subduction factory

[R6-07] Primary magma of Cretaceous Northern Kyushu batholith: New approach from Cumulus rocks

*Keisuke ESHIMA¹, Masaaki OWADA¹, Atsushi KAMEI² (1. Yamaguchi Univ. Sci. , 2. Shimane Univ.)

Keywords:Cretaceous Northern Kyushu Batholith, Kita-taku mafic complex, Cumulate, Primary magma, Sanukitic HMA

The Jurassic to Cretaceous igneous rocks associated with the subduction of the Izanagi Plate are widely developed in the Northeast Asian continental margin and have been intensively studied for their igneous activity and tectonics (Kim et al., 2016, Lithos262, 88–106; Yu et al. et al., 2021, Int. Geol. Rev., 1881920). It is clear that the igneous rocks in the Japanese Islands, as well as the continental side (Northeastern Chin and Korean Peninsula), are related to the subduction (200–50 Ma) of the Izanagi Plate into Eurasia (Seton et al., 2015, Geophys. Res. Lett. 42, 1732–1740), and approximately 30% of Japan archipelago is occupied by plutons, typically granitoid. In addition, large-scale granitic complexes with an area of more than 100 km², known as batholiths, are exposed throughout the Japanese island and compose the major part of this island arc crust. Furthermore, about 80% of the granitoids exposed in Japan are concentrated in the geochnological age range 50–130 Ma (mainly Cretaceous to Paleogene). These continental-scale periodic large-scale igneous events are called Magmatic flare-ups and are very important for the mechanism of generation of large amounts of silicic magma and the evolution of crustal growth processes (Ducea, 2001, GSA Today, 11, 4–10). In this presentation, we discuss a comprehensive study of the Cretaceous Northern Kyushu Batholith, including magma generation mechanisms, especially the formation process and generation mechanisms of source magmas of the granitoids that form the batholith-scaled pluton. In addition, the source magmas will be examined using the Cumulus rocks from the Kita-Taku mafic complex associated with the Cretaceous Northern Kyushu batholith. We believe that the use of the cumulus minerals from the primary magma and the tracing of the characteristics of the primary magma is the best approach in the Northern Kyushu batholith, where there are very few exposures of coeval volcanic rocks (i.e., it is difficult to determine the melt composition from volcanic rocks).