Elasticity of clinopyroxene (Ca, Na) (Mg, Al, Fe) Si2O6 under Earth's upper mantle conditions
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abstract
The Earth's upper mantle is one of the most dynamic layers of our planet and closely related to many tectonic processes adversely affecting human beings. For example, subduction and delamination, which are the two major geological processes of recycling crustal materials into the deep Earth, can result in seismic heterogeneities and anisotropies in the Earth's interior, as well as destructive Earthquakes and volcanisms on the Earth's surface. Therefore, understanding the nature and dynamics of the Earth's upper mantle is not only crucial for studying the mantle composition and convection but also relevant to society. Due to the difficulties of direct sampling, seismology provides by far the most accurate image of the Earth's upper mantle. Sound velocity and density measurements of relevant minerals are essential for understanding upper mantle seismic observations. Clinopyroxene, as a major phase of the Earth's upper mantle (10-30 vol%) and the dominating mineral of eclogite (about 60-70 vol%), is one of the most important yet least studied groups of minerals of the Earth's interior. Eclogite is widely believed to be the main driving force for subduction and delamination because of its high density. Thus direct density measurements of clinopyroxene at high pressure (P)-temperature (T) conditions are needed for calculating the buoyancy of eclogite in the Earth's interior. In addition, clinopyroxene is the most anisotropic major mineral in the Earth's upper mantle. It is also the only phase that contributes to any observed anisotropy of eclogite. Explanation of seismically observed upper mantle anisotropy requires knowledge of single-crystal elasticity of clinopyroxene at real Earth P-T conditions. Previous experimental studies have been limited mainly to high-symmetry materials, such as garnet, under P-T conditions far less than those expected in the Earth's interior. The purpose of this study is to measure the density and single-crystal elasticity of clinopyroxene in-situ, implement the optical system that is needed to complete the proposed experiments at University of New Mexico, apply the obtained experimental results to real Earth, and create unique opportunities for graduate and undergraduate students, especially underrepresented minority students, to participate in scientific research at the state-of-the-art experimental facilities both on campus and at national laboratories.
The investigators will use synchrotron single-crystal micro-diffraction and single-crystal Brillouin spectroscopy combined with CO2 laser heating or resistive heating methods to systematically investigate the thermoelastic properties (including density and single-crystal elasticity) of clinopyroxene with different chemical compositions up to 1800K and 18 GPa, covering the entire stability field in the Earth's upper mantle. The obtained experimental result will be used to assist seismic interpretation and geodynamical modeling, which will eventually contribute to our understanding of the origin and nature of the anisotropy and heterogeneity observed in the Earth's upper mantle.
