Diamonds and their inclusions as thermometers and clocks; deep carbon records the evolution of the lithosphere

点击翻译按钮获取中文摘要

Project Background The continents and associated lithospheric mantle are old with complicated histories but critically they can record key developments in the geodynamic evolution of the Earth. For example, they may track periods of extensive partial melting associated with elevated mantle temperatures or provide insights into the timing of the beginning of subduction through the accretion of cool oceanic lithosphere. Therefore, a robust method to extract the thermal history of the lithosphere would allow us to distinguish such models. Nitrogen defects in diamonds and specifically, the time and temperature-dependent evolution of these defects has long been used to estimate the residence temperature of diamonds in the mantle. Recently we have developed a more sophisticated approach for zoned diamonds which, in combination with radiometric dating of diamond inclusions, enables us to calculate long-term secular heating or cooling rates for diamond-containing lithosphere that can be used to evaluate thermal and geodynamic models for the evolution of the lithosphere. Project Aims and Methods The overall aim of the project is to establish the mode of formation and subsequent evolution of continental lithosphere in different localities around the world. We have access to a unique collection of diamonds from Canada, Australia, Southern Africa, Siberia and South America and have the connections to obtain others if required, so can apply our approach to gain a global overview of lithospheric evolution. The basic idea is to date inclusions in zoned diamonds using radiogenic isotopes, then look at the evolution of nitrogen defects within the diamond lattice (see background reading) to model the thermal history of the diamonds and their hosting lithospheric mantle. This requires characterising and selecting the right inclusions, some novel isotope geochemistry and code development to model the defect aggregation and extract the thermal history. There is therefore quite a lot of flexibility in how the student might wish to specialise as the project progresses.