[3ch301-12] R1 [Regular Session]Plutonic rocks, volcanic rocks and magmatic processes

[R1-O-9] Magma source of San-yo and Ryoke belt granites and fluid-rock interaction of silicoeus veins and Ryoke metamorphic belt schists

*HAFIZ U. REHMAN¹, YAMAMOTO Hiroshi¹ (1. Kagoshima University)

Keywords:Ryoke belt, San-yo belt, granites, oxygen isotope data, partial melting

Oxygen isotope results (δ¹⁸O) of quartz are presented for the San-yo and Ryoke belt granites, associated metamorphic rocks (pelitic schists, siliceous schists), and two generations of siliceous veins (foliation-parallel and foliation-normal) that exist in pelitic and siliceous schists. Purified quartz grains from the above-mentioned lithologies were analyzed for δ¹⁸O using the conventional fluorination method. Quartz grains showed δ¹⁸O values (relative to VSMOW) of 9.7 to 12.9 ‰ in granites, 15.1 to 17.3 ‰ in biotite schist, and 16.4 to 17.8 ‰ in siliceous schist. The δ¹⁸O values of quartz from foliation-parallel veins in biotite schist were 16.6 ‰ whereas quartz grains from the foliation-normal veins in biotite schist had δ¹⁸O values of 17.3 ‰. The δ¹⁸O values of quartz in the investigated granite samples are comparatively higher than usually found in the typical I-type granites (ca. 5–8 ‰) and show some overlap with the S-type granites (ca. 9–12 ‰). These features suggest that the source magma of Ryoke and San-yo these granites was likely derived from the partial melting of the chemically modified crust with sedimentary precursors. Hafnium isotope data of zircons from the same granites, reported in an earlier publication (Mateen et al., 2019, Geosciences Journal 23, 917-931), exhibited by Ɛ_Hf (t) values between +1.1 and -4.8 provide additional evidence for the formation of the granites from a continental crust with some incorporation of the reworked older crustal material that was hydrothermally altered before partial melting. The relatively higher δ¹⁸O values (> 15 ‰) of quartz in foliation-parallel and foliation-normal veins indicate their precipitation from the silica- and ¹⁸O-rich fluids that were extracted from the slab-dehydration process during late-stages of their evolution.　Detailed results can be seen elsewhere (Rehman et al. 2021, Journal Episodes).

References
Mateen et al., 2019. Geosciences Journal 23, 917-931
Rehman et al. 2021. Episodes, https://doi.org/10.18814/epiiugs/2021/021012