C and H Retention Mechanisms in the Deep Earth

University Of California-Santa Cruz, Santa Cruz CA

Investigators

Abstract

The cycling of carbon and water between the Earth’s rocky interior and its surface is critical for the genesis and long-term evolution of oceans and atmosphere. It influences the composition, melting, and viscous flow of the planet’s solid mantle. The genesis of continents, the production of most volcanism, and likely plate tectonics itself hinge on the way carbon and water (or its constituent hydrogen) are stored within the Earth and released from its interior. Yet, measuring C and H chemical properties at mantle conditions is challenging, because of the extreme pressures and temperatures prevailing at depth. Here, the researchers investigate experimentally how C and H are stored within the minerals present in the mantle. They also test the conditions in which these minerals persist or release these elements. The team develops and uses state-of-the-art high-pressure devices to reproduce the mantle’s extreme conditions. During the experiments, they explore the way C and H behave in their host minerals at various pressures and temperatures. Their tools are powerful X-rays at a national synchrotron facility, and infrared and laser light in their home laboratory. The project also provides support and training for graduate and undergraduate students at the University of California Santa Cruz. It is co-funded by the NSF Geophysics program and Petrology and Geochemistry program. The team conducts single-crystal X-ray diffraction and vibrational spectroscopic measurements (Infrared and Raman) at room and high temperature in the diamond anvil cell, where extreme pressures are produced at the tips of two opposing diamonds. The researchers investigate a sequence of carbonated and hydrated phases of interest for volatile retention and cycling within Earth. Phases that are relevant for both the planet’s volatile budget and the sequestration of incompatible elements are probed. Specifically, the project aims to: (1) characterize the shifting bonding environment of the carbonate unit in targeted phases under compression - a unit that may undergo anomalous bonding changes at high pressures; and (2) probe at an unprecedent resolution the high-pressure structure of the hydrated phase whose stability field most closely approaches the conditions of the mid- to deep-upper mantle. The team also continues to augment and test the capabilities of a community-accessible, high-pressure/high-temperature single crystal X-ray diffraction facility located at the Advanced Light Source at Lawrence Berkeley National Labs. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.