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ANR ORISULF – english version

Start: 01/04/2023 - End: 01/10/2026

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The origin of volatile elements on Earth is a central question for understanding how our planet was formed. Various scenarios suggest volatiles were sourced
either from the inner or outer solar system, and were delivered to Earth early or late in the accretion sequence. The various models have widely distinct implications for the dynamics of our young solar system.

ORISULF will place original constraints on the origin of volatiles on Earth. ORISULF will focus on the sulfur geochemical systematics, rather than focusing on species that are prone to have their primordial signature shuffled by mantle-surface exchanges, such as water or nitrogen.

ORISULF will tackle the question of volatiles origin in two step.

First, it will deliver a test to the hypothesis that  Earth’s mantle has a non-chondritic 34S/32S. This notion would suggest that Earth’s
sulfur was isotopically fractionated during planetary differentiation. It would require sulfur and other volatiles to have been delivered early during
planetary formation, certainly not by the late veneer. However, it relies entirely on the study of lavas, which are known to experience sulfide-melt
equilibria. In order to determine the true  34S/32S of Earth’s mantle, away from the limitation of sulfide-melt potential fractionations, ORISULF will
target well-characterized peridotites from the European sub-continental mantle.
This will deliver the true 34S/32S of Earth’s mantle and constrain the relative timing of sulfur delivery to Earth.

An equally important second approach will be to characterize with high precision 33S and 36S anomalies in Earth and
extraterrestrial materials. Groups of chondrites from the outer and inner solar system will be characterized. Isotopic signatures from the outer solar system
will be tracked systematically in all major chondrite types. Comparing chondrites to Earth’s rocks will allow ORISULF to disambiguate an inner and
outer solar system origin for Earth’s sulfur and other volatiles.

For further information, feel free to contact Jabrane Labidi.