Copper isotopes track the Neoproterozoic oxidation of cratonic mantle roots.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 38773097.
- Also identified by DOI 10.1038/s41467-024-48304-2 and PMC identifier 11109192.
- 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
The oxygen fugacity (fO<sub>2</sub>) of the lower cratonic lithosphere influences diamond formation, melting mechanisms, and lithospheric evolution, but its redox evolution over time is unclear. We apply Cu isotopes (δ<sup>65</sup>Cu) of ~ 1.4 Ga lamproites and < 0.59 Ga silica-undersaturated alkaline rocks from the lithosphere-asthenosphere boundary (LAB) of the North Atlantic Craton to characterize fO<sub>2</sub> and volatile speciation in their sources. The lamproites' low δ<sup>65</sup>Cu (-0.19 to -0.12‰) show that the LAB was metal-saturated with CH<sub>4</sub> + H<sub>2</sub>O as the dominant volatiles during the Mesoproterozoic. The mantle-like δ<sup>65</sup>Cu of the < 0.59 Ga alkaline rocks (0.03 to 0.15‰) indicate that the LAB was more oxidized, stabilizing CO<sub>2</sub> + H<sub>2</sub>O and destabilizing metals. The Neoproterozoic oxidation resulted in an increase of at least 2.5 log units in fO<sub>2</sub> at the LAB. Combined with previously reported high fO<sub>2</sub> in peridotites from the Slave, Kaapvaal, and Siberia cratonic roots, this oxidation might occur in cratonic roots globally.