Shallow recycling of lower continental crust: The Mahoney Seamount at the Southwest Indian Ridge

Woelki D, Salters V, Beier C, Dick H, Koepke J, Romer R (2023)

Publication Type: Journal article

Publication year: 2023

Journal

Earth and Planetary Science Letters Elsevier

Book Volume: 602

Article Number: 117968

DOI: 10.1016/j.epsl.2022.117968

Abstract

The Mahoney Seamount is a recently discovered volcanic edifice located 4 km north of the ultra-slow spreading Southwest Indian Ridge (SWIR). The SWIR is one of the slowest spreading ridges worldwide with a full spreading rate of ∼14 mm/year and low magmatic productivity. We report that highly vesicular basalts from the Mahoney Seamount have unradiogenic Nd-Hf together with radiogenic Sr isotopic compositions. Their distinct low ²⁰⁶Pb/²⁰⁴Pb isotope signature combined with high ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb is best explained by melting of a mantle that has been strongly influenced by stranded lower continental crust. The geographic distribution of the isotopic variability favors the idea of shallow recycling of lower continental crust isolated for a longer period contributing to melts forming Mahoney Seamount through off-axis fault systems. The isotopic composition of Mahoney Seamount lavas shares many characteristics with EM-1 sources and the DUPAL signature. Previous isotopic studies of the SWIR basalts proposed recycling of ancient subcontinental lithospheric mantle (SCLM) or pelagic sediments with oceanic crust to be responsible for this enriched isotopic signature. Lu/Hf and Sm/Nd ratios of pelagic sediments would result in decoupled ¹⁴³Nd/¹⁴⁴Nd and ¹⁷⁶Hf/¹⁷⁷Hf ratios. This decoupling is also observed in Ejeda-Bekily dikes from Madagascar, but those are believed to sample the SCLM dispersed in the Indian Ocean. However, Mahoney Seamount shows no decoupling in those isotopic systems and the restricted occurrence of the extreme lower continental crustal signature at Mahoney Seamount implies that the enriched isotopic signature has a different origin.

Authors with CRIS profile

René Romer Lehrstuhl für Endogene Geodynamik

Involved external institutions

Helsingin yliopisto / University of Helsinki

Finland (FI) Florida State University (FSU)

United States (USA) (US) Woods Hole Oceanographic Institute

United States (USA) (US) Gottfried Wilhelm Leibniz Universität Hannover

Germany (DE)

How to cite

APA:

Woelki, D., Salters, V., Beier, C., Dick, H., Koepke, J., & Romer, R. (2023). Shallow recycling of lower continental crust: The Mahoney Seamount at the Southwest Indian Ridge. Earth and Planetary Science Letters, 602. https://dx.doi.org/10.1016/j.epsl.2022.117968

MLA:

Woelki, Dominic, et al. "Shallow recycling of lower continental crust: The Mahoney Seamount at the Southwest Indian Ridge." Earth and Planetary Science Letters 602 (2023).

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