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

Oxygen isotope data (delta O-18) of quartz are reported for the San-yo and Ryoke belt granites, metamorphic rocks, and late-stage siliceous veins. The analyzed quartz showed delta O-18 values of 9.7-12.9 parts per thousand (relative to VSMOW) in granites, 15.1-17.3 parts per thousand in biotite schist, 16.4-17.8 parts per thousand in siliceous schist. The delta O-18 values of quartz in foliation-parallel and -normal veins are 16.6 parts per thousand and 17.3 parts per thousand, respectively. The delta O-18 values of quartz in the granite samples are relatively higher than those crystallized from I-type granite magma (ca. 5-8 parts per thousand) and similar with values of S-type granite magma (ca. 9-12 parts per thousand). 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 epsilon(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 delta O-18 values (> 15 parts per thousand) of quartz in siliceous veins indicate their precipitation from silica- and O-18-rich fluids that were extracted from the slab-dehydration process during late-stages of their evolution.