Giulia Marras [Sapienza University of Rome, Italy]

Title: Mineral inclusions in eclogitic diamonds from the Siberian craton: a window into the redox conditions of the Archean mantle

Language:  English presentation

Time: 10:00 - 11:00 AM, Friday, February 23, 2024

Place:  Onsite：Conference room A417, HPSTAR (Beijing)  

Online:  Tencent Meeting:https://meeting.tencent.com/dm/83Ewdt8V1Hzs  Meeting ID: 946-570-061

Host:  Dr. Yanhao Lin

Abstract:

Subduction is the main carrier of oxidized material into the deep mantle and has a key role in changing the mantle redox state (i.e., the oxygen fugacity, fo2) and controlling the volatiles cycle (C, O, H, S, N, B). Kimberlite-borne eclogites are the result of metamorphic processes that the ancient oceanic crust (protolith) underwent upon subduction and are considered fertile source rocks for diamonds. Eclogitic diamonds (E-type) represent the 33% of the extracted lithospheric diamonds, with garnet, clinopyroxene and sulfide being the most frequent retrieved mineral inclusions. Due to the inert nature of diamonds, the trapped minerals can provide pristine and valuable information about the chemistry, mineralogy and redox state of the eclogite source. In addition, the chemistry of the bulk rock, once reconstructed, allows constraining the nature of the protolith. In this study, we investigated a suite of 19 E-type diamonds from the Udachnaya pipe (Siberian craton) with inclusions of both garnet and clinopyroxene, focusing on the chemistry (major elements and V concentration) and Fe3+/ΣFe ratio measured through in situ synchrotron micro-Mössbauer spectroscopy. The results will be presented in terms of i) the fo2 recorded by inclusions in E-type diamonds in comparison to eclogitic xenoliths, ii) the nature of the subducted protoliths and fo2 of the convecting mantle source, and iii) the redox evolution of the eclogitic mantle over time.

Brief introduction of the speaker: 

Giulia Marras is a PhD student in Earth Sciences from Sapienza University of Rome. Her research is focused on redox processes in the Earth’s interior and their role in diamond formation, metasomatism, partial (redox) melting and mobilization of volatile and trace elements to the atmosphere. She studies natural mantle-derived samples like xenoliths (peridotites and Archean eclogites) and mineral inclusions trapped in lithospheric and sublithospheric diamonds using innovative synchrotron-based techniques such as X-ray tomography, diffraction, Mössbauer and nanoFTIR, combined with thermodynamic modelling. Additionally, she investigated the liquid structure of sulfides at HP-T.