Solidus and liquidus profiles of chondritic mantle: Implication for melting of the Earth across its history

International audienc

Thermal Conductivity of FeS and Its Implications for Mercury's Long‐Sustaining Magnetic Field

Co-auteur étrangerInternational audienceThe MESSENGER mission revealed that Mercury's magnetic field might have operated since 3.7–3.9 Ga. While the intrinsic magnetism suggests an active dynamo within Mercury's core, the mechanism that is responsible for sustaining the dynamo for prolonged period of time remains unknown. Here we investigated the electrical conductivity of Fe‐S alloys at pressure of 8 GPa and temperatures up to 1,700 K. We show that the electrical conductivity of Fe‐S alloys at 1,500 K is about 103 S/m, 2 orders of magnitude lower than the previously assumed value for dynamo calculations. The thermal conductivity was estimated using the Wiedemann‐Franz law. The total thermal conductivity of FeS is estimated to be ~4 Wm/K at the Mercurian core‐mantle boundary conditions. The low thermal conductivity suggests that a thermally driven dynamo operating on Mercury is more likely than expected. If coupled with chemical buoyancy sources, it is possible to sustain an intrinsic dynamo during time scales compatible with the MESSENGER observations

182W evidence for core-mantle interaction in the source of mantle plumes

Tungsten isotopes are the ideal tracers of core-mantle chemical interaction. Given that W is moderately siderophile, it preferentially partitioned into the Earth's core during its segregation, leaving the mantle depleted in this element. In contrast, Hf is lithophile, and its short-lived radioactive isotope 182Hf decayed entirely to 182W in the mantle after metal-silicate segregation. Therefore, the 182W isotopic composition of the Earth's mantle and its core are expected to differ by about 200 ppm. Here, we report new high precision W isotope data for mantle-derived rock samples from the Paleoarchean Pilbara Craton, and the Réunion Island and the Kerguelen Archipelago hotspots. Together with other available data, they reveal a temporal shift in the 182W isotopic composition of the mantle that is best explained by core-mantle chemical interaction. Core-mantle exchange might be facilitated by diffusive isotope exchange at the core-mantle boundary, or the exsolution of W-rich, Si-Mg-Fe oxides from the core into the mantle. Tung-sten-182 isotope compositions of mantle-derived magmas are similar from 4.3 to 2.7 Ga and decrease afterwards. This change could be related to the onset of the crystallisation of the inner core or to the initiation of post-Archean deep slab subduction that more efficiently mixed the mantle