Deep evolution of carbonated magmas controls ocean island basalt chemistry.
basic_science · Level V
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- Record sourced from PubMed, PMID 40480984.
- Also identified by DOI 10.1038/s41467-025-60619-2 and PMC identifier 12144093.
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Abstract
The composition of ocean island basalts (OIBs) is key to understanding mantle differentiation and quantifying intra-plate carbon outflux. Existing petrogenesis models fail to simultaneously reproduce the low SiO<sub>2</sub> and low SiO<sub>2</sub>/FeO<sup>T</sup> characteristics of alkalic OIBs and ignore melt-orthopyroxene reactions in the lithosphere that may further elevate the SiO<sub>2</sub> content of primary magmas. Here we show experimentally that high-degree (>50%) high-pressure crystallization of carbonated primary magmas at the base of lithosphere drastically reduces both the SiO<sub>2</sub> content and SiO<sub>2</sub>/FeO<sup>T</sup> ratio, due to the combined effects of clinopyroxene and garnet precipitation and carbonates dissolution. The major-element chemistry of alkalic OIBs can be quantitatively reproduced by considering varying degrees of crystallization, melt-orthopyroxene reactions, and source CO<sub>2</sub> content. Our results imply high intra-plate carbon outfluxes and support the observed association of low OIB SiO<sub>2</sub> contents with low mantle potential temperatures, as slower magma transport at lower temperatures leads to more extensive crystallization and reaction.