22-EPN3-113: Isotopic constraints on deformation of olivine: a preliminary study on mantle peridotites from Mt. Melbourne, northern Victoria Land, Antarctica

Visit by Daeyeong Kim and Jung Hun Seo of the Korea Polar Research Institute (KOPRI, Korea) to TA2.10 Stable, Rare Gas and Radiogenic Isotope Facility at CRPG (France).
Dates of visit: 17 August – 06 September 2023

Report Summary: Microstructures of olivine-rich rocks record tectonic events in mantle, due to their diverse slip systems associated with the various deformation conditions. There have been, however, no time constraints on the slip systems that generate the microstructures of olivine. This study first investigates the temporal relationship of various microstructures of olivine based on the Re-Os geochronology of included sulphides. Mantle xenoliths of one lherzolite and two harzburgites were collected near Mt. Melbourne, northern Victoria Land, Antarctica, which suffered several tectonic events during the Proterozoic and Phanerozoic eons. Sulphide grains are texturally associated with olivine deformation fabrics in mantle rocks. The Re-Os isotopes of the 18 sulphide grains collected from the mantle xenoliths were analysed by using multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) and negative-ion thermal ionization mass spectrometry (TIMS) at CRPG Nancy, France.

The measured Os quantities are 0.9–4789.3 pg and Re quantities are 4.3–7.0 pg in the sulphides. ¹⁸⁷Os/¹⁸⁸Os in the sulphide are 0.1250–0.1298 for J04-A, 0.1130–0.1185 and 0.1286 for J04-B, and 0.1203–0.1216 for J04-D1. The corresponding depleted mantle ages (T_RD) are calculated to be 0.26–0.63 Ga for J04-A, 1.5–2.3 and 0.14 Ga for J04-B, and 1.1–1.3 Ga for J04-D1. The ages correspond to the tectonic evolution of suturing, subducting, and rifting events of the studied area, implying that the various structural events preserved in the mantle xenoliths can be temporally constrained by the sulphide Re-Os geochronology.

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