Journal Article

Subducted Carbon From Mantle Plume in Mid‐Ocean Ridge Basalts

Zhang, Haitao, Huang, Fang, Li, Chuanshun, Yan, Quanshu, Shi, Xuefa, Wen, Qiuyu

2025

Overview

Deciphering the Earth's deep carbon cycle, from mantle plumes to mid‐ocean ridges, remains incompletely understood. In this study, we analyze the magnesium isotope composition of basalts collected from the South Mid‐Atlantic Ridge (SMAR), which have been influenced by the off‐axis Saint Helena plume originating from the core‐mantle boundary. The magnesium isotope composition of SMAR basalts falls within a similar range (−0.22 to −0.32‰; average −0.25‰ ± 0.03‰) to that of known global oceanic basalts. However, isotope mixing calculations suggest that the lighter magnesium isotope composition in the SMAR basalts is due to the incorporation of approximately 5%–10% recycled carbonate material carried by the Saint Helena plume into the SMAR asthenosphere. This finding not only highlights the interaction between ridges and off‐axis plumes but also proposes a comprehensive model for the Earth's deep carbon cycle, spanning from the subduction zone through the core‐mantle boundary to the mid‐ocean ridge system. Plain Language Summary The investigation of the Earth's deep carbon cycle is crucial for elucidating the processes of material transport within the Earth's interior and mantle convection. Despite significant advancements, understanding the complete carbon cycle still presents challenges, particularly in relation to the process of carbon transfer from subducted ancient oceanic crust to the generation of new oceanic crust. By exploring the interaction between mantle plumes and mid‐ocean ridges (MORs), it is possible to achieve a more comprehensive understanding of the intricate Earth's deep carbon cycle. In this study, we present precise Mg isotopic data obtained from mid‐ocean ridge basalts (MORBs) in the South Atlantic region. By integrating the Mg isotope and radiogenic isotopic compositions of basalts from the South Mid‐Atlantic Ridge (SMAR) and Saint Helena Island, we have determined that approximately 5%–10% of recycled carbonate material carried by the Saint Helena mantle plume has been transported into the asthenosphere beneath the SMAR system. Our findings contribute to the development of a coherent model of the Earth's deep carbon cycle, tracing the pathway from subduction zones to the core‐mantle boundary and ultimately return to MOR systems. This model provides valuable insights for geologists seeking to comprehend the material cycle of the Earth. Key Points The composition of Mg isotope in basalts suggests interaction of the Saint Helena plume and South Mid‐Atlantic Ridge system Subducted carbon from the Saint Helena plume has been transported to the South Mid‐Atlantic Ridge system Carbon derived from the subduction zone has the potential to transport to the core‐mantle boundary and return to the mid‐ocean ridge system

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: Asthenosphere / Basalt / Carbon / Carbon cycle / Carbonates / Chemical composition / Earth / Earth axis / Earth mantle / Earth's deep carbon cycle / Geologists / interaction between mantle plumes and mid‐ocean ridges / Isotope composition / Magnesium / magnesium isotope / Magnesium isotopes / Mantle convection / Mantle plumes / mid‐ocean ridge basalts / Oceanic convection / Oceanic crust / Oceans / Plumes / Ridges / South Mid‐Atlantic Ridge / Subduction / Subduction (geology) / Subduction zones