Metamorphic CO₂ Degassing in the Active Himalayan Orogen: Exploring the Influence of Orogenic Activity on the Long-Term Global Climate Changes

Abstract

A number of studies suggest that mountain ranges have strong impact on the global carbon cycle; metamorphic degassing from active collisional orogens supplies a significant fraction of the global solid-Earth derived CO₂ to the atmosphere, thus playing a fundamental role even in today’s Earth carbon cycle. The Himalayan belt, a major collisional orogen still active today, is a likely candidate for the production of a large amount of metamorphic CO₂ that may have caused changes in long-term climate of the past, present and near future. Large metamorphic CO₂ fluxes are facilitated by rapid prograde metamorphism of big volumes of impure carbonate rocks coupled with facile escape of CO₂ to the Earth’s surface. So far, the incomplete knowledge of the nature, magnitude and distribution of the CO₂-producing processes hampered a reliable quantitative modeling of metamorphic CO₂ fluxes from the Himalayan belt. This study, integrated in the framework of the Ev-K2-CNR SHARE (Stations at High Altitude for Research on the Environment) Project, focuses on the metamorphic decarbonation processes occurring during the Himalayan collision. We hereby present preliminary results focusing on the distribution of different types of metacarbonate rocks in the Eastern Himalaya, their petrographic description and the first reported petrological data about the nature of the CO₂-producing reactions in garnet-bearing calc-silicate rocks. These results represent a contribution toward a better understanding of the influence exerted by orogenic processes on climatic changes at global scale.