Metamorphic devolatilization of subducted oceanic metabasalts: implications for seismicity, arc magmatism and volatile recycling

• Published in: Earth and planetary science letters Vol. 189; no. 1; pp. 19 - 29
• Main Authors: Kerrick, D.M., Connolly, J.A.D.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 30.06.2001
• Subjects: carbon dioxide; Marine; metabasalt; metamorphism; subduction; volatilization; subduction; carbon dioxide; metamorphism; metabasalt; volatilization
• ISSN: 0012-821X; 1385-013X
• DOI: 10.1016/S0012-821X(01)00347-8

Subducted oceanic metabasalts are believed to be a primary source of volatiles for arc magmatism and fluid-induced seismicity. From phase equilibria computed for an average oceanic metabasalt we present a model for subduction zone devolatilization for pressures up to 6 GPa (∼180 km). Along high temperature geotherms complete dehydration occurs under forearcs, whereas dehydration does not occur along low temperature geotherms. For intermediate geotherms, major dehydration occurs under subarcs and provides a subjacent H 2O source for arc volcanism. Decarbonation is negligible along cold and intermediate geotherms and limited along high temperature geotherms. Because decarbonation is limited for all subducted carbonate-bearing lithologies, transfer of CO 2 from subducted slabs to arc magmas may be triggered by aqueous fluid infiltration. Metabasalt devolatilization could induce seismicity in forearcs (high temperature geotherms) and subarcs (intermediate geotherms); however, because of the lack of devolatilization, metabasalts would not be a fluid source for seismicity with low temperature geotherms. Along low temperature geotherms, limited devolatilization of subducted oceanic metabasalts and marine sediments in forearcs and subarcs provides a mechanism for return of volatiles to the deeper mantle.