Zinc Isotope Constraints on Recycled Oceanic Crust in the Mantle Sources of the Emeishan Large Igneous Province

Abstract

Identification of the nature of recycling crustal materials in the sources of large igneous provinces (LIPs) is crucial for understanding compositional heterogeneity of the deep mantle. To provide new constraints on this issue, here we reported high‐precision zinc isotope data on picritic and basaltic lavas from the Emeishan LIP, SW China. Using olivine‐melt Mg‐Fe equilibrium and log (incompatible elements)‐log (MgO) systematics, the parental magma of picritic lavas is estimated to have a MgO content of 21.8 wt.%. All picrites and basalts analyzed have δ66ZnJMC 3‐0749L values of ~0.30‰, which is heavier by ~0.14‰ than that of the terrestrial mantle (0.16 ± 0.05‰, 2s.d.). Olivine and clinopyroxene phenocrysts in picrites are isotopically lighter by ~0.15‰ than the whole rocks, and a negative correlation between Zn and MgO contents for picrites is observed, indicating that olivine accumulation could lower Zn contents and δ66Zn values of the magmas. Taking this into account, the parental magma of picrites has a δ66Zn value of 0.33 ± 0.04‰ (2s.d.). This value is significantly higher than that of other large‐degree partial melts derived from the mantle (e.g. Archean komatiites and the Baffin Island picrites; ~0.20‰), which requires addition of recycled crustal materials into the mantle sources. Modeling suggests that this difference can be best explained by partial melting of a hybridized mantle source containing ~15% recycled basaltic oceanic crust. Our data also show no evidence for recycled marine carbonates into the source of Emeishan LIP and thus possibly into the Earth's deep mantle (>660 km).

Mg and Zn Isotope Evidence for Two Types of Mantle Metasomatism and Deep Recycling of Magnesium Carbonates

“…The δ 26 Mg values of the studied alkali basalts (−0.44 ± 0.03‰ to −0.33 ± 0.02‰) are detectably lower than those of the mantle (−0.25 ± 0.04‰) and, thus, unable to have been caused by partial melting or fractional crystallization. Zinc isotopes may be fractionated during crystal‐melt differentiation involving olivines that are isotopically lighter than the melts (McCoy‐West et al, 2018; Sossi et al, 2015; Yang & Liu, 2019), but detectable fractionation (~0.1‰) only occurs at the very end of the differentiation sequence when MgO falls below 3 wt.% as observed in the Kilauea Iki lavas (Chen et al, 2013). The studied alkali basalts have near‐primary compositions (MgO = 8.7–12.2 wt.%) and have δ 66 Zn values above the trend of Kilauea Iki lavas (Chen et al, 2013) as well as of global OIBs (Beunon et al, 2020; Wang et al, 2017) (Figure 7a).…”

Nature of the Mantle Plume Under the Emeishan Large Igneous Province: Constraints From Olivine‐Hosted Melt Inclusions of the Lijiang Picrites

“…component in the Emeishan LIP (Tian et al, 2017). A Zn isotope study has also shown that the δ 66 Zn values of Emeishan picrites and basalts ranges from 0.24‰ to 0.34‰, which is not compatible with the presence of carbonatitic components in the sources of the Emeishan LIP, but may be the joint consequence of the addition of recycled oceanic crust and mantle melting (C. Yang & Liu, 2019).…”

“…Recently, some studies have proposed that recycled materials in the Emeishan mantle plume played a key role in producing the observed compositional diversity of the Emeishan LIP (Bai et al., 2014; Hou et al., 2013; C. Yang & Liu, 2019; Yu et al., 2014; L. Zhang et al., 2019). C. Yang and Liu (2019) and L. Zhang et al. (2019) estimated an oceanic crust component of ∼15% in the source of the Emeishan LIP.…”

“…Zhang et al, 2019). C. Yang and Liu (2019) and L. Zhang et al (2019) estimated an oceanic crust component of ∼15% in the source of the Emeishan LIP. Using the Zn isotopes of basalts, C. Yang and Liu (2019) inferred that marine carbonate components were not present in the source of the Emeishan basalts.…”

Zinc Isotopes of the Mariana and Ryukyu Arc‐Related Lavas Reveal Recycling of Forearc Serpentinites Into the Subarc Mantle

“…Generally, the basalts from the MMT and MOT have MORB-like δ 66 Zn values with slightly higher δ 66 Zn values than those of the NMA, SMA, and SOT basaltic lavas (Figure 4). The δ 66 Zn values of the NMA, SMA, and SOT basaltic lavas fall within the range of the normal mantle (+0.18 ± 0.06 ‰, 2SD; Figure 4a; Doucet et al, 2020;Sossi et al, 2018; and are all lower than those of the global MORB (0.27 ± 0.05‰, 2SD; , ocean island basalts (OIB) (Beunon et al, 2020;Chen et al, 2013;, South China Sea basalts (0.22-0.31‰; Liao et al, 2020), the Kamchatka-Aleutian arc lavas , and East China basalts (Liu et al, 2016;Yang & Liu, 2019) (Figure 4a). The δ 66 Zn values of andesites and dacites from the Mariana and Ryukyu subduction zones also fall within the range of the normal mantle compared to those of the OT rhyolites (Figure 4b).…”