R6: Plutonic rocks, volcanic rocks and subduction factory

[R6-P-01] Sr-Nd isotopic characteristics of Cretaceous to Paleogene plutonic rocks in southwestern Japan

*Shogo KODAMA¹, Masaaki Owada², Mariko Nagashima², Atsushi Kamei³ (1. Taiheiyo Consultant Co., LTD., 2. Yamaguchi Univ., 3. Shimane Univ.)

Keywords:

Cretaceous,Plutonic rocks,Isotopic composition

We discuss the secular change of the mantle wedge composition and the regional variation of the isotopic composition of the Cretaceous to Paleogene Tertiary plutonic rocks in southwest Japan. Since 140 Ma, the increase in the plate subduction rate in the eastern margin of East Asia and the supply of sediments to the mantle wedge due to tectonic erosion have caused the isotopic composition of the mantle wedge to become heterogeneous and enriched over time. The composition of the isotopically enriched primitive basaltic magma at 92 Ma can be reproduced by mixing sediment-derived melt and mantle-derived melt in a 7:3 ratio, adding olivine to the simple mixed melt, and fractionating orthopyroxene and phlogopite. In this study, we propose the MACH model, which describes the process of mixing in the mantle wedge (simple Mixing), the subsequent assimilation fractional crystallization (AFC) with the mantle, and the compositional change, including the isotopic composition (Compositional cHange).