Dear Colleagues, We invite contributions on the nature of carbon-bearing fluids/melts and processes related to them, for the approaching 2024 *European Mineralogical Conference. * The session is entitled**“*Origin and composition of CO2-bearing fluids and melts as transport agents between mantle and crust*”,**and a short description is below. The EMC will take place in *Dublin* between the *18**th**and 23^rd  of August* 2024 (see www.emc-2024.org/ <www.emc-2024.org/>). Abstract submission is open until *the 22nd of March* (https://emc-2024.org/abstract-submission/). It's our pleasure to announce *Patrizia Fumagalli *(University of Milan) as our keynote speaker; Patrizia will be talking about the physical properties of carbonatitic melts. We are looking forward to your contribution. Melanie Sieber, Antonio Acosta-Vigil _Session description:_ COH‑fluids, and volatile-rich silicate and carbonatitic melts, are key agents transporting heat and mass between mantle and crust, producing the geochemical differentiation of Earth and the genesis of ores, and controlling the deep cycle of volatiles such as CO_2 and H_2 O through geologic time. Such fluids and melts play a profound role in various tectonic settings. For instance, fluids released from the subducted slab metasomatize the mantle wedge to eventually produce arc magmas, which let continental crust grow. Magmatism in collisional orogens and anorogenic intraplate settings are important for the growth and differentiation of continental crust as well. Fluids also modulate the exchange and recycling of material, such as carbon, between Earth’s mantle reservoirs and surface. In addition to the major role on carbon distribution of subduction-related fluids, carbonatitic melts are often associated with continental rift-related settings. All these processes triggered by COH‑fluid and melts are strongly dependent on their chemical and physical properties. Over the last years much progress has been made to characterize the origin and main properties of deep, CO_2 ‑bearing fluids and melts, such as their volatile and trace element content. This session aims to bring together scientists from a broad range of disciplines to discuss the origin, nature and processes involving COH‑fluids and volatile-rich silicate and carbonatitic melts. We welcome contributions based on, but not limited to, field observation, petrology and geochemistry, experimental petrology, and numerical and thermodynamic modeling. In particularly, we invite discussion on (i) major and trace element composition of deep fluids, (ii) petrological records of CO_2 ‑bearing fluids and melts (e.g. melt/fluid inclusions, metasomatised xenoliths, and multicomponent mineral‑fluid/melt systems), (iii) implications on crustal growth and differentiation, ore deposit genesis, and deep volatile cycles; and (iv) the establishment and applications of novel analytical techniques, computational models, and interdisciplinary approaches. -- Dr. Melanie Sieber ____________________________________________________________ University of Potsdam Institute of Geosciences Phone: +49 331 977 5671 Fax: +49 331 977 5700 Karl-Liebknecht-Strasse 24-25, D-14476 Potsdam German Research Centre for Geoscience (GFZ) Helmholtz Centre Potsdam Section 3.6 Chemistry and Physics of Earth Materials Phone: +49 331 288 1378 Fax: +49 331 288 1402 Telegrafenberg, D-14473 Potsdam Geo.X ECS Representative