Final Report Summary - HABITABLEPLANET (Creating a habitable planet: the roles of accretion, core formation and plate tectonics)
The Earth is a dynamic planet, composed of a central metallic core surrounded by a convecting rocky outer mantle and rigid tectonic plates. Interactions between the planet’s mantle take place during tectonic processes such as subduction, where one tectonic plate plunges beneath another into the Earth’s deep mantle. The goal of this project has been to use novel isotope fingerprinting tools to study the chemical reactions that take place during these tectonic processes and subsequent magmatic activity and to understand if plate tectonics has completely mixed the Earth’s mantle or if mineralogically distinct material still remains within the Earth’s interior. We have been able to prove that considerable quantities of sulfur and economically-important elements like the transition metals are released from plates by oxidised fluids as they subduct below the Earth’s surface. This is a major step forward in our understanding of the cycling of metals between the Earth’s surface, interior, oceans and atmosphere, with implications for the chemistry of magmas erupted at the Earth’s surface, the gases released from volcanoes and the concentration of economically-important elements near the surface in the form of ore deposits. We have also been able to place further constrains on the behaviour of sulfur in magmas and have demonstrated that the behaviour of sulfur and transition elements in magmas is controlled by their tectonic setting and magma ascent through the Earth’s mantle to the surface. Finally, we have been able to show that while most of the mantle has been homogenised through the processes of plate tectonics and early crust formation discrete pockets of mineralogically distinct material still remain and are sampled by modern mantle plumes and hotspots.