Variations in stable isotope compositions (δ13C, δ18O) of calcite within exhumation-related veins from the Sanbagawa metamorphic belt

Abstract

Stable isotope compositions (δ13C, δ18O) of calcite within the veins hosted by the Sanbagawa metamorphic rocks in the Nagatoro area, Kanto mountains, Japan gave clues on movement of fluids during exhumation. The host rock calcite shows the nearly uniform δ18O values ranging from +14.5 to +16.5‰ (V-SMOW), and wide δ13C variation from −12.1 to +1.3‰ (V-PDB). The δ13C values of calcite within the exhumation-related veins also have wide variation, and the Δhost-vein (= δ13Chost rock-δ13Cvein) value vary depending on vein thickness and textures. Thin stretched crystal veins contain calcite with δ13C value close to that of the host rock calcite (Δhost-vein < ±2‰). In contrast, calcite grains within the thick blocky veins have homogenous δ13C values with large variations with host rock (Δhost-vein = +3.5 - −3.0‰). The latter types of sealed cracks may have played as dominant pathways of regional fluid flow.