R6: Plutonic rocks, volcanic rocks and subduction factory

[R6P-01] Compositional changes in closed and open systems of igneous rocks from northern part of Mt. Shaku-dake, northern Kyushu, SW Japan

*Keisuke ESHIMA¹ (1. Yamaguchi Univ.)

Keywords:Cretaceous Northern Kyushu Batholith, Porphyry, Mixing, Hydrothermal alteration

Recently, diorite (HMD) with high Mg andesite (HMA) compositions have been reported from Cretaceous mafic rocks in northern Kyushu. Examples include the Kunisaki Peninsula, Kita-taku (Kamei et al., 2004), Mt. Shaku-dake and Mt. Ushikiri-yama areas (Eshima et al., 2020; Eshima, 2021; Eshima and Owada, 2023). These mantle-derived mafic magmas are considered to be strongly involved in the genesis of granitic magmas as parent magmas and heat sources for crustal melting (Reid et al., 1983), and are very important rocks for a comprehensive understanding of the magmatic relationships of the Cretaceous Northern Kyushu batholith and the growth process of the granitic crust. On the other hand, it is very important to examine the geological and petrological relationship between the HMA (HMD) and the surrounding rocks that were active at the same time to elucidate the origin of the HMA magma and its maturation process (including tectonics). Such an examination will expand our understanding of igneous activity with HMA activity to a comprehensive understanding that includes volcanic-plutonic activity and geological time scales. In this presentation, I discuss the compositional changes of igneous rocks including porphyritic rocks in the northern part of Mt. Shaku-dake area, Mt. Shaku-dake body is as known as the largest HMD body in northern Kyushu, in closed and open systems, and discuss the plutonism of the Cretaceous igneous activity in the early stage of the Cretaceous Northern Kyushu batholith.