Pyroxenes provenance signature on East and West Antarctic Ice-Sheet dynamics during the Plio-Pleistocene transition (IODP Expedition 374, Site U1523)

The mineralogy of pyroxenes analyzed from IODP sediments and cores (Site U1523, Exp. 374 – Ross Sea) represents an exceptional archive and provenance proxy for tracing source rocks and reconstructing the history of sediment erosion and transport in Antarctica. This study helps us assessing the provenance of sediments sampled in the Ross Sea, derived from the West Antarctic Rift System (WARS), from the Transantarctic Range (TAM), and from the East Antarctic Ice Sheet (EAIS), during the different glacial and interglacial periods of the Quaternary. The rocks derived from Cenozoic Magmatism-Volcanism, located in the Ross Sea and WAIS, are linked to an active rifting system dominated by markedly alkaline products, such as the Mount Erebus tephra, in which the presence of anorthoclase and green augite are a distinctive fingerprint of this eruptive center. The optical and spectroscopic characteristics of its minerals are unique, with the full-width mode width (FWHM) of clinopyroxenes reflecting the rapid cooling kinetics, typical of effusive rocks and pyroclastic products. In Continental Magmatism and Volcanism (TAM/EAIS), we find traces of the fragmentation of the supercontinent Gondwana, and this geodynamic environment is characterized by a subalkaline/tholeiitic signature, together the presence of an ancient Paleozoic metamorphic basement. In the Ferrar Group (Lower Jurassic), we find a predominantly tholeiitic magmatic suite (KCFB – Kirkpatrick Continental Flood Basalts). This suite contains a complex and diagnostic pyroxene association with orthopyroxene: Enstatite, Hypersthene with marked and diagnostic pleochroism in pale pink, pink-green, and dark pink-green tones; brown titaniferous augite and pigeonite. In the doleritic dykes (Intermediate/Hypoabyssal Intrusive rocks), we recognize colorless diopside, with intermediate order of crystallization in the crystal lattice of clinopyroxene. Aegirine (sodium clinopyroxene) is also found locally in the Alkaline Volcanism, associated with late alkaline intrusions. Metamorphic and non-magmatic rocks predominate in the metamorphic basement, and pyroxenes are rare, but highly ordered from a crystallographic point of view. Thanks to this high-resolution study merging optical microscopy and Raman spectroscopy, it was possible to distinguish the different magmatic environments (deep, intermediate, and shallow) and their provenance from different sources, both in terms of formation age and geological provinces (Ferrar Jurassic vs. Cenozoic volcanism). By cross-referencing petrographic data, pyroxene mineralogical species, and varieties adding the Raman order and disorder dataset (FWHM), a new approach is being applied to provenance studies in these regions. This will allow us to more precisely characterize the sediment mineralogy during glacial and interglacial periods and to distinguish pyroxenes originating from different glacial basins that contribute to the sedimentological record in the Ross Sea through the geological time.