Search for: All records

Unraveling the origin(s) of carbon on Earth has remained challenging, not only because of the multiple isotopic fractionation episodes that may have occurred during planet formation processes but also because the end point of these processes, the current isotopic value of Earth’s deep carbon reservoirs remains poorly constrained. Here, we present carbon isotopic measurements on rare undegassed mid-ocean ridge basalts from the Pacific, Atlantic, and Arctic Oceans that have preserved the isotopic signature of their mantle source. We find that Earth’s present-day convecting upper mantle has variable δ¹³C value from ~−10 to −4‰, significantly different from the δ¹³C value of peridotitic diamonds and with the highest values being restricted to the Atlantic. Evidence for significant mantle heterogeneity contrasts with previous assumptions and its origin remains puzzling being uncorrelated with geochemical markers associated with either subduction and surficial recycling processes or lower mantle contributions. The data do not preclude other causes such as primordial mantle heterogeneity. We suggest that the δ¹³C value of the bulk silicate Earth may need to be revised. 

Abstract Slab surface temperature is one of the key parameters that incur first-order changes in subduction dynamics. However, the current thermal models are based on empirical thermal parameters and do not accurately capture the complex pressure–temperature paths of the subducting slab, prompting significant uncertainties on slab temperature estimations. In this study, we investigate whether the dehydration-melting of glaucophane can be used to benchmark the temperature in the slab. We observe that dehydration and melting of glaucophane occur at relatively low temperatures compared to the principal hydrous phases in the slab and produce highly conductive Na-rich melt. The electrical properties of glaucophane and its dehydration products are notably different from the hydrous minerals and silicate melts. Hence, we conclude that the thermodynamic instability of glaucophane in the slab provides a unique petrological criterion for tracking temperature in the present-day subduction systems through magnetotelluric profiles.