Abstract

Viscosity measurements for the upper mantle imply that on a large-scale, over geological periods of time, the upper mantle should be a relatively well-mixed reservoir within the Earth. However, ocean-scaled geochemical differences across the upper mantle have been known since the 1980’s, with the identification of isotopic anomalies such as the DUPAL anomaly and SOPAL . Furthermore, isotopic characteristics of depleted, Indian Ocean mid-ocean-ridge-basalts (MORB), which is often synonymous with the DUPAL anomaly, have been documented in Neo-Tethys and Paleo-Tethys MORB prior even to the formation of the Indian Ocean, suggesting that perhaps the upper mantle is not so well mixed as we might anticipate. However, it is not clear how isotopic anomalies could persist in the upper mantle through successive plate re-organisations given the 100-1000’s millions of years of radiogenic ingrowth necessary to generate differences in depleted mantle composition. I will explore this question using 3D spherical numerical mantle circulation models embedded with geological paleo-tectonic reconstructions.