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Tracking the Earth’s mantle through space and time.

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Department of Earth Sciences

3 South Parks Road

Oxford

OX1 3AN

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Dr Tiffany Barry (University of Leicester) will give Oxford Geology Group's Wager Lecture for Sepetember 2019.

ABSTRACT:

Large-scale geochemical signatures within the upper mantle have been known since the 1980’s (e.g. 1,2,3), including the DUPAL and SOPAL anomalies. The depleted, Indian Ocean mid-ocean-ridge-basalt signature, synonymous with the DUPAL anomaly, has been documented beyond today's Indian Ocean ridges, into Neo-Tethys and Paleo-Tethys before it (e.g. 4,5). Whilst such observations have been documented, it is not clear how isotopic anomalies can persist in the upper mantle through successive plate re-organisations. We can explore this question using 3D spherical numerical mantle circulation models embedded with up-to-date geological plate reconstructions and ground-truthed with robust Hf-Nd isotope data. Using such techniques, it appears that areas of the Earth’s mantle remain largely isolated from full mantle convection, within cells defined by the positions of subducting plates. Compelling evidence suggests that large-scale convection cells produce a dominantly ‘up-down’ convective pattern, where material at the core-mantle boundary (CMB) is returned to the upper mantle geographically above it. The models fit global patterns of isotope data and can explain long-lived features such as the DUPAL anomaly and differences between Indian and Pacific Ocean crust. Indeed, the new geochemical data suggests this mode of convection could have influenced the evolution of mantle composition well beyond the timeframe of the mantle circulation models, potentially since at least the start of the Paleozoic.

Refs: 1. Dupré, B. & Allègre, C.J. Nature 303, 142-146 (1983). 2. Staudigel, H. et al. EPSL 102, 24-44 (1991). 3. Hart, S.R. Nature 309, 753-757 (1984). 4. Mahoney, J.J. et al., J. Pet. 39, 1285-1306 (1998). 5. Xu, J. et al., 2002EPSL 198, 323-337.

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Department of Earth Sciences

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Oxford

OX1 3AN

United Kingdom

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