Mantle Hg isotopic heterogeneity and evidence of oceanic Hg recycling into the mantle

Runsheng Yin,Xinbin Feng,Bernd Lehmann,Xieyan Song,Di Chen,Chuanwei Zhu,Joel D Blum,Liemeng Chen,Songyue Yu,Xun Wei,Yue Xu,Changzhou Deng,Xin Pan

doi:10.1038/s41467-022-28577-1

Abstract

The geochemical cycle of mercury in Earth’s surface environment (atmosphere, hydrosphere, biosphere) has been extensively studied; however, the deep geological cycling of this element is less well known. Here we document distinct mass-independent mercury isotope fractionation (expressed as Δ199Hg) in island arc basalts and mid-ocean ridge basalts. Both rock groups show positive Δ199Hg values up to 0.34‰ and 0.22‰, respectively, which deviate from recent estimates of the primitive mantle (Δ199Hg: 0.00 ± 0.10‰, 2 SD)1. The positive Δ199Hg values indicate recycling of marine Hg into the asthenospheric mantle. Such a crustal Hg isotope signature was not observed in our samples of ocean island basalts and continental flood basalts, but has recently been identified in canonical end-member samples of the deep mantle1, therefore demonstrating that recycling of mercury can affect both the upper and lower mantle. Our study reveals large-scale translithospheric Hg recycling via plate tectonics.

Highlights

The geochemical cycle of mercury in Earth’s surface environment has been extensively studied; the deep geological cycling of this element is less well known
Hg isotopes in ocean island basalts, suggests that crustal Hg is recycled into the lower mantle[1]
mid-ocean ridge basalts (MORBs) and island arc basalts (IABs) have δ202Hg ranging from −1.58 to −0.50‰ and −1.72 to 0.13‰, with similar mean values of −0.93 ± 0.62‰ (2 SD) and −0.80 ± 1.22‰ (2 SD), respectively

Summary

Introduction

The geochemical cycle of mercury in Earth’s surface environment (atmosphere, hydrosphere, biosphere) has been extensively studied; the deep geological cycling of this element is less well known. The more negative values of δ202Hg in OIBs and CFBs (that are genetically related to the lower mantle) relative to those of MORBs and IABs (that originate from the upper mantle), as shown, could possibly be explained by more severe Hg degassing during the eruption of the latter compared to the former.

Results

Conclusion