Low-degree melt metasomatic origin of heavy Fe isotope enrichment in the MORB mantle

Guo, Pengyuan; Niu, Yaoling; Chen, Shuo; Duan, Meng; Sun, Pu; Chen, Yanhong; Gong, Hongmei; Wang, Xiaohong

Abstract

Studies of mid-ocean ridge basalts (MORB) show a variable Fe isotope composition of the oceanic upper mantle. To test a recent hypothesis that heavy Fe isotope enrichment in the MORB mantle results from the same process of incompatible element enrichment, we conduct an Fe isotope study of well-characterized MORB samples from a magmatically robust segment (OH-1) of the Mid-Atlantic Ridge (MAR) at ∼ 35°N. The data show large Fe isotope variation (Fe = +0.03 to +0.18‰) that correlates well with the abundances and ratios of more-to-less incompatible elements and with Sr-Nd-Hf isotopes. Our findings in support of the hypothesis can be detailed as follows: (1) the oceanic upper mantle has a heterogeneous Fe isotope composition on varying small spatial scales with isotopically heavy Fe (high-Fe) preferentially associated with pyroxenite lithologies; (2) such lithologies, which are also enriched in the progressively more incompatible elements, are of low-degree (low-F) melt metasomatic origin; (3) with all the conceivable processes considered, the low-F melt metasomatism takes place at the lithosphere-asthenosphere boundary (LAB) beneath ocean basins through crystallization of incipient (Low-F) melt in the seismic low velocity zone (LVZ) at the base of the growing oceanic lithosphere (i.e., LAB) over the Earth's history since the onset of plate tectonics, forming composite lithologies with geochemically enriched pyroxenite veins dispersed in the depleted peridotite matrix; (4) such mantle of composite lithology when transported to beneath the present-day ocean ridges will undergo decompression melting and produce MORB melts with geochemical trends of “melting-induced mixing” as observed at the MAR and global MORB; (5) we predict all this to be a globally common process and widespread.

Citation

Guo, P., Niu, Y., Chen, S., Duan, M., Sun, P., Chen, Y., …Wang, X. (2023). Low-degree melt metasomatic origin of heavy Fe isotope enrichment in the MORB mantle. Earth and Planetary Science Letters, 601, Article 117892. https://doi.org/10.1016/j.epsl.2022.117892

• Journal Article Type: Article
• Acceptance Date: Oct 28, 2022
• Online Publication Date: Nov 9, 2022
• Publication Date: 2023
• Deposit Date: Oct 24, 2023
• Publicly Available Date: Oct 24, 2023
• Journal: Earth and Planetary Science Letters
• Print ISSN: 0012-821X
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 601
• Article Number: 117892
• DOI: https://doi.org/10.1016/j.epsl.2022.117892
• Public URL: https://durham-repository.worktribe.com/output/1816390