Recycled Carbonate‐Bearing Silicate Sediments in the Sources of Circum‐Mediterranean K‐Rich Lavas: Evidence From Mg‐Zn Isotopic Decoupling

Abstract

The solid Earth contains more carbon than the entire surface reservoir (ocean, atmosphere, and biosphere) in terms of mass: over 90% of carbon is located in the crust, mantle, and core (Dasgupta & Hirschmann, 2010;Wood, 1993). Carbon is released from the Earth's interior mainly in the form of carbon dioxide (CO 2 ) by degassing from volcanoes (up to 90%) and metamorphic reactions (≈10%; Mason et al., 2017). The flux of CO 2 released from oceanic volcanism (mid-ocean ridges and ocean islands) is ∼29-154 Megatons per year (Mt/yr) (Kelemen & Manning, 2015), and the global flux of CO 2 emitted from other volcanic environment, including plume degassing and diffuse degassing, is up to ∼108 Mt/yr (Werner et al., 2019), which has a significant time-integrated impact on the concentration of atmospheric CO 2 (161 × 10 3 Mt; Lee et al., 2019). The circum-Mediterranean region, which experienced a prolonged period of convergence between the African-Arabian and the Eurasian plates from the late Jurassic to Cenozoic (Prelević & Foley, 2007), contributes an anomalously large flux of subaerial volcanic CO 2 emissions (20.1 Mt/yr;Werner et al., 2019), accounting for about 20% of the global total. This

Tracing Sediment Melt Activity in the Sub‐Continental Lithosphere: Insights From Zn‐Fe Stable Isotopes

“…Recently, Shu et al. (2023) revealed that recycled carbonate‐bearing silicate sediments could induce Mg‐Zn isotopic decoupling in mantle‐derived magmas, especially in the case of low carbonate fractions in the sediments. Continental margin sediments (0.07‰ ± 0.11‰; Little et al., 2016) have a significantly lighter Zn isotopic signature than normal mantle, and these sediments can be incorporated into the continental mantle through subduction erosion (Straub et al., 2020).…”

“…Furthermore, considering that mantle partial melting would slightly enrich the melt with heavy Zn isotopic compositions (e.g., Sossi et al, 2018;Wang et al, 2017), the mantle source of parental melts for clinopyroxenites should have a lighter Zn isotopic composition (<0.04‰). Recently, Shu et al (2023) revealed that recycled carbonate-bearing silicate sediments could induce Mg-Zn isotopic decoupling in mantle-derived magmas, especially in the case of low carbonate fractions in the sediments. Continental margin sediments (0.07‰ ± 0.11‰; Little et al, 2016) have a significantly lighter Zn isotopic signature than normal mantle, and these sediments can be incorporated into the continental mantle through subduction erosion (Straub et al, 2020).…”

Sediment recycling at the slab-mantle interface andfore-arc metasomatism: experimental production ofK-rich metasomes

“…This is also in accordance with the recent studies investigating the fate of the CO 2 in the upper mantle, underscoring that the Tethyan subduction might have transported a much larger amount of CO 2 than previously assumed 71,76,81 . Moreover, it is also recently proposed that the recycled carbonate sediments are responsible for low δ 26 Mg and high δ 66 Zn signatures observed in the Mediterranean lamproites defining so-called "Mg-Zn isotopic decoupling" 82 .…”

Fractionation of Nb/Ta during subduction of carbonate-rich sediments

“…Zn-Mg isotope compositions in other circum-Mediterranean magmas suggests the recycling of marls (Shu et al, 2023). In the area, high precision HFSE data are available for the Rhodopes (Bulgaria) and Santorini (Kirchenbaur and Münker, 2015).…”