Enigmatic carbon isotopic variability in the oceanic upper mantle

• 成果类型: Article
• 署名作者: Moussallam, Yves; Rose-Koga, Estelle F.; Aubaud, Cyril; Georgeais, Guillaume; Cartigny, Pierre; Koga, Kenneth T.; Devidal, Jean-Luc; Michael, Peter J.; Shimizu, Kei; Saal, Alberto E.
• 署名单位: Columbia University; Bureau de Recherches Geologiques et Minieres (BRGM); Centre National de la Recherche Scientifique (CNRS); Universite de Orleans; CNRS - National Institute for Earth Sciences & Astronomy (INSU); Universite Paris Cite; Centre National de la Recherche Scientifique (CNRS); Universite Clermont Auvergne (UCA); Institut de Recherche pour le Developpement (IRD); Centre National de la Recherche Scientifique (CNRS); University of Tulsa; University of Wisconsin System; University of Wisconsin Madison; Brown University
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.2502886122
• 发表日期: 2025-06-24
• 页码: e2502886122
• 关键词: carbon isotopes; upper mantle; undersaturated melts; mid-ocean ridge basalts; volatile elements; mid-atlantic ridge; co2; fractionation; 14-degrees-n; geochemistry; systematics; volatiles; basalt; h2o/ce; record

摘要

Unraveling the origin(s) of carbon on Earth has remained challenging, not only because of the multiple isotopic fractionation episodes that may have occurred during planet formation processes but also because the end point of these processes, the current isotopic value of Earth's deep carbon reservoirs remains poorly constrained. Here, we present carbon isotopic measurements on rare undegassed mid-ocean ridge basalts from the Pacific, Atlantic, and Arctic Oceans that have preserved the isotopic signature of their mantle source. We find that Earth's present-day convecting upper mantle has variable delta C-13 value from similar to-10 to -4 parts per thousand, significantly different from the delta C-13 value of peridotitic diamonds and with the highest values being restricted to the Atlantic. Evidence for significant mantle heterogeneity contrasts with previous assumptions and its origin remains puzzling being uncorrelated with geochemical markers associated with either subduction and surficial recycling processes or lower mantle contributions. The data do not preclude other causes such as primordial mantle heterogeneity. We suggest that the delta C-13 value of the bulk silicate Earth may need to be revised.