[SMP39-P04] Stable isotope study of carbonate associated with antigorite serpentinite: O–C isotope characterization of a textually zoned calcite rock from the Itoigawa–Omi area, Japan
Keywords:antigorite serpentinite, metasomatic rock, carbon isotope, oxygen isotope, amphibolite-facies
Despite the zoned texture and the different mineral assemblage, systematic stable carbon and oxygen isotope analyses using by micro-sampling technique found no clear core-to rim change. δ13C (‰ VPDB) and δ18O (‰ VSMOW) values are from −5.0 to −4.1‰ (average −4.4‰ [n = 34]) and +15.6 to +16.4‰ (average 16.1‰ [n = 34]), respectively. It is noteworthy that δ13C of zoned calcite rock is significantly higher than the δ13C values of graphite (−8.6 to −7.9‰) in jadeitite in the Omi area (Ogawara and Akai, 2014 [doi:10.2465/jmps.131125a]) and also dolomite nodule (−13.4 to −13.6‰; this study) associated with lizardite serpentinite in the Franciscan Complex. Although there are a few possible carbon sources for the calcite rock, the δ13C close to −5‰ might have reflected a mantle-derived carbon. On the other hand, relatively high δ18O values suggest that the calcite-rock-forming aqueous fluids were in equilibrium with metasedimentary rocks.