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

抄録

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 Δ_host-vein (= δ¹³C_{host rock}-δ¹³C_vein) 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 (Δ_host-vein < ±2‰). In contrast, calcite grains within the thick blocky veins have homogenous δ¹³C values with large variations with host rock (Δ_host-vein = +3.5 - −3.0‰). The latter types of sealed cracks may have played as dominant pathways of regional fluid flow.