Abstract
For mid-ocean ridge basalts and ocean island basalts, measurements of Pb isotope ratios show broad linear correlations with a certain degree of scatter. In 207Pb/204Pb—206Pb/204Pb space, the best fit line defines a pseudo-isochron age (τPb) of ∼1.9 Gyr. Previous modeling suggests a relative change in the behaviors of U and Pb between 2.25 and 2.5 Ga, resulting in net recycling of HIMU (high U/Pb) material in the latter part of Earth's history, to explain the observed τPb. However, simulations in which fractionation is controlled by a single set of partition coefficients throughout the model runs fail to reproduce τPb and the observed scatter in Pb isotope ratios. We build on these models with 3D mantle convection simulations including parameterizations for melting, U recycling from the continents and preferential removal of Pb from subducted oceanic crust. We find that both U recycling after the great oxygenation event and Pb extraction after the onset of plate tectonics, are required in order to fit the observed gradient and scatter of both the 207Pb/204Pb—206Pb/204Pb and 208Pb/204Pb—206Pb/204Pb arrays. Unlike much previous work, our model does not require accumulations of subducted oceanic crust to persist at the core-mantle boundary for long periods of time in order to match geochemical observations.
| Original language | English |
|---|---|
| Article number | e2021GC010309 |
| Pages (from-to) | 1-24 |
| Journal | Geochemistry, Geophysics, Geosystems |
| Volume | 23 |
| Issue number | 8 |
| Early online date | 8 Aug 2022 |
| DOIs | |
| Publication status | Published - 16 Aug 2022 |
Bibliographical note
Funding Information:This research was partially funded by the NERC funded consortium, “Mantle volatiles: processes, reservoirs and fluxes” (Grant No. NE/M000397/1) of the Deep Volatiles Programme, the NERC large grant “Mantle Circulation Constrained (MC2): A multidisciplinary 4D Earth framework for understanding mantle upwellings” (Grant No. NE/T012633/1), and also by the School of Earth and Environmental Sciences, Cardiff University. Numerical calculations were undertaken at: (a) ARCHER2, the UK's national high‐performance supercomputer; (b) HAWK, part of Supercomputing Wales, the national high‐performance supercomputing system for Wales. Graphs were produced using the Matplotlib package for Python (Hunter, 2007 ) and we make use of the scientific color map, batlow, for select figures (Crameri et al., 2020 ). Visualizations were produced using Paraview (Ahrens et al., 2005 ). This is Cardiff CRediT Contribution 2.
Publisher Copyright:
© 2022. The Authors.