Carbon dioxide and methane emissions from calcareous-marly rock under stress: experimental tests results

G. Martinelli, P. Plescia


The identified emissions of abiogenic carbon dioxide, carbon monoxide and methane are generally attributed to
volcanic activity or to geochemical processes associated with thermometamorphic effects. In this paper we show
another possible abiogenic source of emission, induced by mechanical, and not thermal, stresses. We investigated
the mechanochemical production of carbon dioxide and methane when friction is applied to marly-type rock
and studied the mechanisms determining the strong CO2 and CH4 emissions observed. A ring mill was used to
apply friction and oriented pressure upon a synthetic calcite-clay mixture of varying proportions. We found that
the CO2 and CH4 release versus the grinding action has a non-linear trend reflecting the behaviour of decreasing
crystallinity, which indicates a close link between crystallinity and gas production. For the CO2 emission, we
propose a release mechanism connected with the friction-induced fractures and the increase in structural disorders
induced by creep in the lattice. The CH4 emission could be explained by a Sabatier reaction in which CO2
and hydrogen are involved to form CH4 and water.


gas geochemistry;earthquake precursors;greenhouse gases

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Published by INGV, Istituto Nazionale di Geofisica e Vulcanologia - ISSN: 2037-416X