Seismic and mineralogical evidence for an iron-rich mega-ultralow-velocity zone beneath Hawai'i.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 41604484.
- Also identified by DOI 10.1126/sciadv.adz1962 and PMC identifier 12851025.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
Mantle plumes beneath major oceanic hot spots appear to be rooted in unusually large structures near the core-mantle boundary, which have markedly reduced seismic wave speeds. The origin of these large ultralow-velocity zones (ULVZs), referred to as mega-ULVZs, remains uncertain partly because of lack of constraints on the relative reduction in shear versus compressional wave speeds (<i>R</i><sub>S/P</sub>). This ratio can give clues into the compositional makeup of the mega-ULVZs. Through joint seismic analysis of core-diffracted <i>P</i> and <i>S</i> waves beneath Hawai'i, we constrain the <i>R</i><sub>S/P</sub> of its mega-ULVZ to 1 to 1.3. Mineralogical modeling reveals that iron enrichment via solid iron-rich magnesiowüstite [(Mg,Fe)O] matches this seismic constraint, independent of modeled ULVZ thickness. Enrichment of metallic iron-rich magnesiowüstite likely enhances the thermal conductivity of mega-ULVZs and provides a mechanism to drive localized plume upwelling. Higher reported <i>R</i><sub>S/P</sub> values for smaller ULVZs near subduction zones may therefore indicate different processes at play controlling ULVZ formation across the diverse core-mantle boundary landscape.