Tracing deep carbon cycling by metal stable isotopes

Li, Shuguang

doi:10.1093/nsr/nwac071

Cited by 2 publications

(1 citation statement)

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“…Some kinds of Mg-rich carbonates have significantly high Zn contents (e.g., 147p.p.m in dolomite and 449p.p.m in magnesite) 47 . Such Mg-rich carbonates are more stable in the subduction zone 3 , 48 , and a considerable proportion of them has the potential to be retained in subducted slabs and finally introduced into the deep mantle, e.g., the mantle transition zone (410–660 km) 48 , 49 . Consequently, recycled carbonate, along with recycled oceanic crust, is a suitable candidate to produce metasomatic carbonatite melts (with variable proportions of silicate composition), which inherit the high δ 66 Zn signature.…”

Section: Resultsmentioning

confidence: 99%

Zinc isotopic evidence for recycled carbonate in the deep mantle

et al. 2022

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Carbonate, the major carbon reservoir on Earth’s surface, can enter into the mantle by subduction. However, evidence for recycled surficial carbonates in the deep mantle is still scarce. Ocean island basalts from Cook-Austral islands and St. Helena Island, widely called HIMU basalts because of their high μ = 238U/204Pb sources, are thought to be fed by mantle plumes originating in the lower mantle. Here we report exceptionally high δ66Zn values (δ66Zn = 0.38 ± 0.03‰) of these HIMU lavas relative to most published data for oceanic basalts (δ66Zn = 0.31 ± 0.10‰), which requires a source contributed by isotopically heavy recycled surficial carbonates. During subduction of the oceanic lithosphere, melting of mixed surficial carbonates and basaltic crust in the deep mantle generates carbonatite melts, which metasomatizes the nearby mantle and the resultant carbonated mantle ultimately evolves into a high-δ66Zn HIMU source. High-δ66Zn signatures of HIMU basalts, therefore, demonstrate that carbonates can be transported into Earth’s deep mantle.

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