Carbon isotope geochemistry of calcite from Late Jurassic microbially altered basalts in the Tokoro belt, eastern Hokkaido, Japan

Abstract

Textural and stable isotopic studies of metabasalts in the Tokoro greenrocks, eastern Hokkaido, Japan, indicate that microbes had a significant role in the alteration of Late Jurassic basaltic glasses. Carbon isotopes (δ¹³C) in calcites from metabasalts also show differences that may relate to microbial activity during alteration before subduction metamorphism. The low (δ¹³C values (ca.-4‰) of calcite were attributed to alteration influenced by Bacteria. Positive δ¹³C values (<1‰) of some samples suggest lithotrophic utilization of CO₂, in which methanogenic Archaea produced CH₄ from H₂ and CO₂.