Polymineralic inclusions in eclogite-facies metapelites from Tanzania – insights on partial melting and geodynamic processes in a 2 Ga old subduction zone

• Applicant: Dr. Petra Herms
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: from 2018 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 405358375

Polymineralic inclusions in high-grade metamorphic rocks are a promising tool to obtain new insights on the formation of partial melts with respect to melt composition, fluid regime and geodynamic setting. All studies on polymineralic inclusions reported so far occur either in anatectic crustal rocks and granulites or in rocks from subducted continental crust.By contrast, the eclogite-facies metapelites of the Usagaran belt in Tanzania represent a part of the subducted oceanic crust, providing the rare opportunity to investigate the process of partial melting in oceanic rocks. Polymineralic inclusions in these metapelites are distinct, because siliceous mica-bearing mineral assemblages occur beside carbonaceous ones indicating the presence of a CO2-dominated COH fluid, with unmixing of melt and/or fluid as a possible formation process. Furthermore, the study area provides the exceptional opportunity to investigate one of the oldest known subduction zones (2 Ga) and the results might shed light on the geothermal gradients in the early Earth’s history.The proposed research shall focus on: (1) Timing and process of melt formation in one of the oldest ancient subduction zones, (2) composition of the melts produced and the influence of the presence of CO2. The samples will be analyzed by means of optical microscopy, electron microprobe, Raman spectroscopy and LA-ICP-MS. Furthermore, the polymineralic inclusions will be rehomogenized by remelting experiments with a piston cylinder.

• DFG Programme: Research Grants
• International Connection: Hungary
• Cooperation Partner: Professor Csaba Scabó
• Co-Investigator: Dr. Christopher Giehl