Elasticity of Pyrope-Almandine-Grossular Garnet Solid Solution Series at High Pressure and Temperature using Ultrasonic Interferometry in Conjunction with Synchrotron Radiation.

Delaware State University, Dover DE

Investigators

Abstract

The deepest drilling into the interior of the Earth is limited to less than 15 km. Consequently, the bulk of its interior is inaccessible to direct sampling, and its structure and mineralogical composition can only be inferred using indirect evidence. Efforts to understand the mineralogy of the Earth?s mantle have combined information from several different fields including seismology, petrology and geochemistry, but the most direct information about the physical structure of the Earth?s deep interior comes from seismology which provides information about variation of the elastic wave velocity and density as a function of depth. Seismic studies have provided models that show rapid increases (velocity jumps or discontinuities) in the seismic waves at 410 to 660 km depths in the Earth and unusually steep velocity gradients in the region between the discontinuities, called the transition zone. Experimental petrological studies of minerals of the upper mantle show that they transform to high-pressure forms at the pressure and temperature conditions of the transition zone. In particular pyroxene, one of the dominant upper mantle minerals in basaltic and peridotitic rocks transforms into the garnet structure at pressure and temperature conditions of the lower regions of the upper mantle and transition zone. In this research program, we propose to systematically measure the pressure and temperature dependence of the elastic properties of the pyrope (Mg3Al2Si3O12?Py) - almandine (Fe3Al2Si3O12-Alm)-grossular (Ca3Al2Si3O12-Gr) solid solutions. We will conduct these experimental studies using specimens synthesized in the Stony Brook High Pressure Laboratory, the techniques of ultrasonic interferometry, and in conjunction with the synchrotron X-ray facilities at the National Synchrotron Light Source of the Brookhaven National Laboratory.