In-situ characterization of the trace element signatures, with special emphasize to the REE pattern, of Ca-rich mineral and fluid inclusions in diamonds from a super-deep source.

• Applicant: Professor Dr. Frank Erich Brenker
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: from 2019 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 427321448

Trace element pattern, including the relative abundance of rare earth elements (REE), are an important tool to decipher the origin and geological history of minerals and rocks. Whereas these signatures and related processes are quite well known for crustal materials and the lithospheric upper mantle, direct data on the deeper Earth are still scarce.Studies of REE of inclusions in diamonds with a suggested super deep origin (asthenospheric upper mantle, transition zone and lower mantle) demonstrate that CaSiO3-perovskite might be the main host of these trace elements within the deep Earth. For most rock chemistries, it is experimentally demonstrated that a CaSiO3-Phase will only exists at pressures related to depths of the lower transition zone and the lower mantle of the Earth. However, it was already shown that at least some of these CaSiO3-inclusions found in super deep diamonds originate in the upper mantle most likely from carbonatitic melts.In this proposal we plan to apply a variety of non-destructive “in-situ” techniques, with special emphasize to novel advanced Synchrotron X-ray beam techniques developed or improved by our group. The main task will be to determine the REE and trace element inventory of a subset of carbonaceous and therefore potentially REE-rich mineral and fluid inclusions in diamonds with a suggested super deep origin. The goal will be to characterize and compare different subsets with various suggested depths and processes of origin. These include inclusions suites with likely lower mantle (CaSiO3+MgSiO3+-MgO), transition zone (CaSiO3+Ringwoodite) or upper mantle (CaSiO3+Ca2SiO4) origin, as well as CaSiO3-CaTiO3 intergrowths, Ca-carbonates, Ca-phosphates and related trapped REE-rich fluids.In contrast to any effort before, based on our new technical developments at DESY (Hamburg) and the ESRF (Grenoble), we are now able to quantitatively determine all REE with a spatial resolution of well below a micron, of inclusions still trapped within the diamond host. This enables to measure very tiny (below 1 micron), very fragile (like carbonates) or very complex inclusions and attached fluid films. This type of measurement is possible by the use of a novel plate detector technology, which enables fast and simultaneous wavelength dispersive X-ray fluorescence analyses of all REE at high spatial resolution (~ 100nm) and low detection limits (< 1ppm). As REE and trace element patterns are crucial to decipher the geological history of minerals and rocks it might help to constrain their origin and source region within the heterogeneous mantle.

• DFG Programme: Research Grants
• International Connection: Belgium, Canada, Italy, USA
• Cooperation Partners: Professor Dr. Fabrizio Nestola; Dr. Steven Shirey; Professor Dr. Thomas Stachel; Professor Dr. Laszlo Vincze