Carbon mobility in subduction zones: in-situ experimental constraints on organic and inorganic carbon transfer at oxidizing conditions

• Applicant: Professorin Carmen Sanchez-Valle, Ph.D., since 9/2024
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 450056892

Carbon represents an essential element for the origin and evolution of life and profoundly contributes to the well-being and sustainability of our planet. Understanding the circulation of carbon at a global scale has been thus a primary goal within the Earth sciences community in recent years. In particular, the study of subduction zone processes has been paramount, as this geological setting represents the main input of carbon into the mantle. In this context, carbon-bearing phases in the slab have a pivotal importance, as at subsolidus conditions, the transfer of carbon is mediated by dissolution processes, triggered by aqueous fluids released from the subducting slab. While carbonate solubility has been extensively investigated, the contribution of reduced carbon forms, such as graphite and hydrocarbons, has been only recently taken into consideration, and its role in the deep carbon cycle remains still debated in literature. During the first funding period, we investigated the dissolution of reduced carbon phases (i.e. crystalline graphite and disorder carbon) in slab-derived silica-bearing aqueous fluids to 2 GPa and 700 °C. We demonstrate that these fluids are efficient carriers of carbon even at mild temperature conditions, i.e., 700 °C, and report on the formation of immiscible hydrocarbons in fluid compositions that mimic the complexity of subduction fluxes. In this proposal, we will extend these studies to investigate the mobility of carbon in subduction zones under more realistic conditions for natural systems. We will particularly focus on constraining the effect of oxidized conditions on the transport of reduced carbon by aqueous fluids at sub-arc conditions. We plan to investigate the dissolution of both crystalline graphite and disordered carbon, as well as the stability of hydrocarbons in silica-bearing oxidized fluids at 2 to 3.5 GPa and 400 to 800 °C, with Raman spectroscopy in hydrothermal diamond anvil cells. The planned experiments will enable to clarify whether reduced carbon can be transferred across the subduction mélange, and eventually reach the mantle wedge. Our in-situ experimental constraints on carbon-bearing aqueous systems in equilibrium with silicate minerals will allow us to further calibrate thermodynamic models based on the Deep Earth Water (DEW) model to provide a quantitative understanding of the extent of carbon recycling in subduction zones.

• DFG Programme: Research Grants
• International Connection: USA
• Cooperation Partner: Professor Dimitri Sverjensky, Ph.D.
• Ehemalige Antragstellerin: Dr. Carla Tiraboschi, until 9/2024