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In this work, we demonstrate a remarkable change of chemical trend of Iron under high pressure that is of great importance for understanding the distribution of elements in the Earth's mantle and core. Using first principles crystal structure search method, we conduct a systematic study of the propensity of p block elements to chemically bind with iron under high pressures ranging from ambient conditions to that of Earth's core. We show that under increasing pressure, iron tends to reverse its chemical nature, changing from an electron donor (reductant) to an electron acceptor, and oxidizes p-block elements in many compounds. Such reverse chemistry has a significant impact on the stoichiometries, bond types and strengths, structures and properties of iron compounds under deep planetary conditions., 21 pages, 11 figures

Supplemental material, Supplemental Material2 for Shipboard Characterization of Tuvalu, Samoa, and Lau Dredge Samples Using Laser-Induced Breakdown Spectroscopy (LIBS) by Jasper G. Konter, Valerie A. Finlayson, Jacqueline Engel, Matthew G. Jackson, Anthony A. P. Koppers and Shiv K. Sharma in Applied Spectroscopy

Supplemental material, Supplemental Material1 for Shipboard Characterization of Tuvalu, Samoa, and Lau Dredge Samples Using Laser-Induced Breakdown Spectroscopy (LIBS) by Jasper G. Konter, Valerie A. Finlayson, Jacqueline Engel, Matthew G. Jackson, Anthony A. P. Koppers and Shiv K. Sharma in Applied Spectroscopy

International audience; Ocean island basalts (OIB) with extremely radiogenic Pb-isotopic signatures are melts of a mantle component called HIMU (high µ, high 238U/204Pb). Until now, deeply dredged submarine HIMU glasses have not been available, which has inhibited complete geochemical (in particular, volatile element) characterization of the HIMU mantle. We report major, trace and volatile element abundances in a suite of deeply dredged glasses from the Tuvalu Islands. Three Tuvalu glasses with the most extreme HIMU signatures have F/Nd ratios (35.6 ± 3.6) that are higher than the ratio (∼21) for global OIB and MORB, consistent with elevated F/Nd ratios in end-member HIMU Mangaia melt inclusions. The Tuvalu glasses with the most extreme HIMU composition have Cl/K (0.11–0.12), Br/Cl (0.0024), and I/Cl (5–6 × 10−5) ratios that preclude significant assimilation of seawater-derived Cl. The new HIMU glasses that are least degassed for H2O have low H2O/Ce ratios (75–84), similar to ratios identified in end-member OIB glasses with EM1 and EM2 signatures, but significantly lower than H2O/Ce ratios (119–245) previously measured in melt inclusions from Mangaia. CO2-H2O equilibrium solubility models suggest that these HIMU glasses (recovered in two different dredges at 2500–3600 m water depth) have eruption pressures of 295–400 bars. We argue that degassing is unlikely to significantly reduce the primary melt H2O. Thus, the lower H2O/Ce in the HIMU Tuvalu glasses is a mantle signature. We explore oceanic crust recycling as the origin of the low H2O/Ce (∼50–80) in the EM1, EM2, and HIMU mantle domains.

A discrepancy between the cartographic depiction of Ta’u Island, Samoan archipelago, in 1849 and its present geomorphology, leads to the impression that a massive collapse involving an estimated 30 km3 occurred on the island’s southern flank less than 170 years ago. It is likely that this flank-collapse, whenever it occurred, generated a tsunami with regional impacts. Here we apply exposure dating to the remnant landslide scarp using the cosmogenic nuclide 36Cl, to show that the flank-collapse occurred 22.4 1.8 ka during the last glacial maximum (LGM). The collapse may have been triggered due to volcanic-related processes, but it is also possible that climatic-eustatic sea-level during the LGM may have played a role in influencing failure of the flank. We confirm that the initial cartographic depiction of Ta’u in 1849 was incorrect, and that this prehistoric landslide-tsunami was not a societal hazard at the time of its occurrence. This is because the Samoan and surrounding Island Nations were only inhabited about 3 ka or so. Nevertheless, we suggest that geomorphic features similar to the Ta’u flank-collapse on analogous islands and seamounts in the Pacific likely represent signatures of landslide-tsunamis in the past. We conclude that there is a need to identify and date other such features in the Pacific, in order to further improve our spatial and geochronological understanding of these events. There is also a need to identify flank features that have not yet failed, and assess the likely mechanisms that could potentially trigger failure. By doing this, we can start assessing with more confidence the hazard potential of similar flank-collapses in future—a risk that is presently under-represented.

Recent Icelandic rifting events have illuminated the roles of centralized crustal magma reservoirs and lateral magma transport1–4, important characteristics of mid-ocean ridge magmatism1,5. A consequence of such shallow crustal processing of magmas4,5 is the overprinting of signatures that trace the origin, evolution and transport of melts in the uppermost mantle and lowermost crust6,7. Here we present unique insights into processes occurring in this zone from integrated petrologic and geochemical studies of the 2021 Fagradalsfjall eruption on the Reykjanes Peninsula in Iceland. Geochemical analyses of basalts erupted during the first 50 days of the eruption, combined with associated gas emissions, reveal direct sourcing from a near-Moho magma storage zone. Geochemical proxies, which signify different mantle compositions and melting conditions, changed at a rate unparalleled for individual basaltic eruptions globally. Initially, the erupted lava was dominated by melts sourced from the shallowest mantle but over the following three weeks became increasingly dominated by magmas generated at a greater depth. This exceptionally rapid trend in erupted compositions provides an unprecedented temporal record of magma mixing that filters the mantle signal, consistent with processing in near-Moho melt lenses containing 107–108 m3 of basaltic magma. Exposing previously inaccessible parts of this key magma processing zone to near-real-time investigations provides new insights into the timescales and operational mode of basaltic magma systems.