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

This work demonstrates distinct mass-independent mercury isotope fractionation in global basalts, which suggests mantle Hg isotope heterogeneity and reveals large-scale translithospheric Hg recycling via plate tectonics. 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 Delta Hg-199) in island arc basalts and mid-ocean ridge basalts. Both rock groups show positive Delta Hg-199 values up to 0.34 parts per thousand and 0.22 parts per thousand, respectively, which deviate from recent estimates of the primitive mantle (Delta Hg-199: 0.00 +/- 0.10 parts per thousand, 2 SD)(1). The positive Delta Hg-199 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 mantle(1), 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.

Automated summary

This study demonstrates distinct mass-independent mercury isotope fractionation in global basalts, revealing mantle Hg isotope heterogeneity and the large-scale translithospheric Hg recycling through plate tectonics.