Assimilation and fractional crystallization of Sanukitic high–Mg andesite–derived magmas, Kyushu Island, southwest Japan: An example of the Cretaceous Shaku–dake diorite body

Anatomy of Shaku–dake high–Mg diorite, southwest Japan: Lithofacies variations and growth process of high–Mg diorite stock

“…In this study, field observations as well as modal, whole-rock, and mineral compositional analyses of the TPD are carried out, and lithofacies variations and the growth process of the TPD body are discussed. Although geochemical variation in the TPD has been reported in previous studies (Eshima and Owada, 2018;Eshima et al, 2020), the focus of the present study is lithofacies variations and the TPD growth.…”

“…2). The geology of this area was described by Eshima et al (2020). The Shaku-dake body, exposed on the western foot of Mt.…”

“…Shaku-dake, consists mainly of TPD and hornblende-biotite granodiorite (HBG) accompanied by four coeval dikes, namely, porphyritic fine-grained tonalite, dolerite, clinopyroxene granodiorite, and fine-grained biotite granite (Fig. 2a; Eshima and Owada, 2018;Eshima et al, 2020). These dikes including HBG dikes randomly intruded the TPD body (Fig.…”

“…The Cretaceous Northern Kyushu batholith was divided into 17 granitic bodies with minor amounts of mafic rocks (Fig. 1; Karakida, 1985;Owada and Kamei, 2010;Eshima et al, 2020). Kamei et al (2004) proposed a discrimination diagram of mafic plutons using the chemical composition of clinopyroxene, of which the chemical characteristics of higher Mg# and Si of clinopyroxene reflected the composition of the source magma, such as high-Mg andesite magma.…”

“…According to this diagram, some mafic plutons in the Northern Kyushu batholith were originally derived from high-Mg andesite magma. Eshima et al (2020) used the discrimination diagram to report that two-pyroxene diorite (TPD) in the Shaku-dake body, a member of the Northern Kyushu batholith, contains clinopyroxene coexisting with the high-Mg andesite magma as well as high Ni and Cr content, according to whole-rock analyses. They further concluded that the TPD was originally derived from high-Mg andesite magma, which had been significantly affected by assimilation and fractional crystallization.…”