Superdeep Diamonds from the Transition Zone and Lower Mantle

Diamond is a remarkable material for its ultimate physical properties, potential technological applications under extreme conditions, but also for its ability to reveal geophysical and geochemical processes in the deep mantle. Mineral inclusions in diamond capture processes involving high pressure, high temperature, fluids, melts, and the dynamic interactions between the Earth’s surface and interior. Recent notable discoveries have been made by studying mineral inclusions in diamond including ice-VII, new rare-earth mineral species, and evidence of H2O in the transition zone and lower mantle. In another recent study, continental roots have been proposed to contain more diamond that previously thought based on seismic velocity structure. Although regions where diamonds form are not average or typical mantle, diamond inclusions present the only direct mineral samples from the Earth’s deepest interior. Aided by technological developments in synchrotron X-ray microtomography and diffraction, more discoveries lie ahead that will inform us on the geodynamics of the crust-mantle system. This proposal explores a new suite of over 150 superdeep inclusion-rich diamonds from Juina, Brazil. Each diamond contains potentially dozens of micro-inclusions, amounting to 103 or more new inclusions for the entire suite that will be analyzed for composition and structure by new high-throughput methods developed by the graduate student. An outstanding question will be addressed by spectroscopic methods: how do we even know superdeep diamonds come from the transition zone and lower mantle? Using GHz-ultrasonic interferometry, the elastic tensor (Cij) of diamond will be measured at high pressure for the first time. In addition, heating experiments on decompression of hydrous phases in diamond-anvil cells will mimic the ascent of high-pressure phases as inclusions to elucidate the back-reaction kinetics and ascent pathways from superdeep origins.