[S-CG73] [JJ] Petrology, Mineralogy and Resource Geology

[SCG73-P21] Petrological study on the mafic igneous enclaves in the Miocene Miuchi granitoid pluton, southern Ehime Prefecture

megumi Shiota², Fuma Yamasaki², *Satoshi SAITO¹ (1.Graduate School of Science and Engineering, Ehime University, 2.Faculty of Science, Ehime University)

Keywords:Miuchi pluton, Granitoid, Mafic igneous enclave

Mafic igneous enclaves with sub-angular shape are commonly occurred in the Miocene Miuchi granitoid pluton, southern Ehime Prefecture. The mafic enclaves (61-64 wt.% SiO₂, 0.5-2.6 wt.% K₂O) are composed mainly of plagioclase, biotite, quartz and opaque minerals. Acicular apatites are common in the mafic enclaves. Intergrowth texture of biotite and quartz/plagioclase are locally observed in the biotite-rich mafic enclaves. K₂O contents of the mafic enclaves increase with increasing SiO₂. Orthopyroxene, locally surronded by biotite, occurs in the mafic enclave with the lowest SiO₂ and K₂O contents. Biotite-rich reaction rim is observed between the orthopyroxene-bearing mafic enclave and host granite. The host granite samples surrounding the mafic enclave are relatively depleted in the K-feldspar (granodiorite in composition) compared to the dominant rock type of the Miuchi granitoid pluton (monzogranite - granite in composition) (67-78 wt.% SiO₂, 3.3-6.5 wt.% K₂O). The petrographic and geochemical characteristics of the mafic enclaves are suggestive of interaction with host granite magmas through hydration crystallization reaction: hydrous granitic melt + pyroxene + Fe-Ti oxides ± calcic plagioclase = biotite + quartz ± sodic plagioclase (e.g. Bard et al. 2005, J. Geol.).