In-situ abiogenic methane synthesis from diamond and graphite under geologically relevant conditions.

Diamond and graphite are fundamental sources of carbon in the upper mantle, and their reactivity with H-rich fluids present at these depths may represent the key to unravelling deep abiotic hydrocarbon formation. We demonstrate an unexpected high reactivity between carbons' most common allotropes, diamond and graphite, with hydrogen at conditions comparable with those in the Earth's upper mantle along subduction zone thermal gradients. Between 0.