S-type / I-type and Ilmenite-series / Magnetite-series zoning within a granitic body: Case study of the Toki granitic body, Central Japan

Abstract

The Toki granite, a single pluton, is located in the Cretaceous Sanyo Belt in the Inner Zone of Southwest Japan. Samples collected from 19 borehole sites in the granite display spatial variations in petrological evidence, indicative of a zoned pluton consisting of three rock facies from the margin to the interior: muscovite-biotite granite (MBG), hornblende-biotite granite (HBG) and biotite granite (BG). ASI ( Mol Al2O3 / (CaO+Na2O+K2O) ), Al2O3, K2O and Na2O change systematically from MBG through HBG to BG, corresponding to a systematic variation from S-type granite in the margin to I-type in the interior. Fe3+ / Fe2+ gradually increase from MBG through HBG to BG, corresponding to a systematic change from ilmenite-series type in the margin to magnetite-series type in the interior.