Petrological evidence for deep subduction of organic carbon to subarc depths

Abstract

The significance of subducted organic carbon for the deep carbon cycle has been demonstrated by the presence of ultra-deep diamonds and arc emissions. However, there is no convincing evidence that organic carbon can be subducted to subarc depths. This study provides the evidence for deep subduction of sedimentary organic carbon to mantle depths through petrological observation, Raman and isotopic analyses of ultrahigh-pressure (UHP) coesite- and graphite-bearing pelitic schists. The analyzed graphite shows light δ13C values (−24.7 to −22.5‰), indicating a sedimentary organic carbon source. Petrological characteristics of graphite co-existing with coesite in garnet and P–T calculations suggest that organic graphite was subducted to the subarc depths exceeding 90 km. This research represents the petrological evidence for the deep subduction of organic carbon to mantle depths and may provide insight into the origin of diamonds with light δ13C values and contribute as key evidence for the Lomagundi event.