Carbon in the Deep Earth: A Mineral Physics Perspective
Sarah Palaich Heffern, University of California, Los Angeles
Carbon is an essential component of life on Earth and plays a role in the carbon cycle at the surface of the Earth. Beyond these surface interactions lies the deep carbon cycle. This cycle controls the flux of carbon subducting into the earth and provides clues as a possible carbon reservoir in the deep earth. The studies included in my dissertation examine various forms of carbonate under high pressure and high temperature conditions found in the deep earth. Carbon is subducted as carbonate in calcite, aragonite and dolomite, as elemental carbon or as CO2. To achieve the high pressures experienced by subducting material, diamond anvil cells are used to expose milligrams of material to extreme conditions. The experiments detailed here were conducted using a wide range of diamond anvil cell techniques and the data were collected at numerous synchrotron and neutron diffraction facilities across the globe including the Advanced Light Source at Lawrence Berkeley National Laboratory, the Spallation Neutron Source at Oak Ridge National Laboratory and the European Synchrotron Radiation Facility at Grenoble, France. These experiments are the result of fruitful collaborations that brought scientists from around the globe together to study the thermoelastic properties of carbonate and CO2. I found important thermoelastic properties for the following minerals: hanksite, tychite, kutnohorite, aragonite and carbon dioxide. Each study yields isothermal bulk modulus data and the studies on aragonite and carbon dioxide also yield thermal expansion data. The equation of state, phase stability and thermoelastic data derived from these experiments will inform models of planetary interiors while giving insight into the evolution of carbon at the high pressures and temperatures of Earth’s interior.