Pervasive subduction zone devolatilization recycles CO2 into the forearc

• Published in: Nature communications Vol. 11; no. 1; pp. 6220 - 8
• Main Authors: Stewart, E. M., Ague, Jay J.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 04.12.2020; Nature Publishing Group; Nature Portfolio
• Subjects: 119/118; 704/2151/209; 704/2151/431; 704/47/4113; Carbon dioxide; Decarbonation; Devolatilization; Humanities and Social Sciences; Lava; Mathematical models; multidisciplinary; Numerical models; Numerical prediction; Rocks; Science; Science (multidisciplinary); Subduction (geology)
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-020-19993-2

The fate of subducted CO 2 remains the subject of widespread disagreement, with different models predicting either wholesale (up to 99%) decarbonation of the subducting slab or extremely limited carbon loss and, consequently, massive deep subduction of CO 2 . The fluid history of subducted rocks lies at the heart of this debate: rocks that experience significant infiltration by a water-bearing fluid may release orders of magnitude more CO 2 than rocks that are metamorphosed in a closed chemical system. Numerical models make a wide range of predictions regarding water mobility, and further progress has been limited by a lack of direct observations. Here we present a comprehensive field-based study of decarbonation efficiency in a subducting slab (Cyclades, Greece), and show that ~40% to ~65% of the CO 2 in subducting crust is released via metamorphic decarbonation reactions at forearc depths. This result precludes extensive deep subduction of most CO 2 and suggests that the mantle has become more depleted in carbon over geologic time. The fate of subducted CO 2 remains debated, with estimates mainly from numerical predictions varying from wholesale decarbonation of the shallow subducting slab to massive deep subduction of CO 2 . Here, the authors present field-based data and show that ~40% to ~65% of the CO 2 in subducting crust is released via metamorphic decarbonation reactions at forearc depths.