Oxygen isotope data of quartz from San-yo and Ryoke belt granites, schists, and siliceous veins: constraining the effects of ¹⁸O-rich fluids on granitic magma

Abstract

Oxygen isotope data (δ 18 O) of quartz are reported for the San-yo and Ryoke belt granites, metamorphic rocks, and late-stage siliceous veins. The analyzed quartz showed δ 18 O values of 9.7-12.9‰ (relative to VSMOW) in granites, 15.1-17.3‰ in biotite schist, 16.4-17.8‰ in siliceous schist. The δ 18 O values of quartz in foliation-parallel and -normal veins are 16.6‰ and 17.3‰, respectively. The δ 18 O values of quartz in the granite samples are relatively higher than those crystallized from I-type granite magma (ca. 5-8‰) and similar with values of S-type granite magma (ca. 9-12‰). These features suggest partial melting of the chemically modified crust with sedimentary precursors to form the parental magma of granites. Hafnium isotope data of zircons from those granites, reported in an earlier publication, exhibited by ε 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 hydrothermally altered reworked crust before partial melting. The relatively higher δ 18 O values (> 15‰) of quartz in siliceous veins indicate their precipitation from silica-and 18 O-rich fluids that were extracted from the slab-dehydration process during late-stages of their evolution. 1 8 O values ca. +5.7±0.3‰ but exhibit a wider range if basalts/gabbros are altered ca. 0 to +12‰ (Kolodny