Research Cafe


 Melissa Sims

Melissa Sims

PhD candidate in the Department of Geosciences

'Simulating Meteorite Impact in the Diamond Anvil Cell'

Synopsis:  We study the phase diagram of the plagioclase ((Na1-x Cax)Al1+x Si2-x O8) system as a function of strain-rate, overpressure, and temperature. The objective is to determine the effect of the pressure-temperature (loading) path on plagioclase phase formation and preservation during impact events. Plagioclase is a mineral that is ubiquitous on rocky bodies throughout the solar system; particularly on the Earth, numerous meteorites, and in lunar mare and highlands. It can be altered through shock metamorphism. Shock results from impacts between planetary bodies and plays an important role in secondary processing in the solar system. As pressures and temperatures increase, plagioclase proceeds through stages of deformation (brittle fracture, plastic deformation), formation of maskelynite and a high pressure polymorph, and finally terminates in melting. Impactites are characterized based on methods that use static and shock experiments to gage pressure and temperature conditions based on phase formation during impacts. These experiments have differences in timescale, temperature, path, and strain-rate compared to each other or natural events. For some phases, the experiments can have large discrepancies in formation pressure. We utilize a new diamond anvil cell (DAC) technique, rapid compression, combined with laser heating and in situ synchrotron X-ray diffraction in order to study previously inaccessible loading paths. Rapid compression allows DAC experiments to change pressure while observing. The method allows independent constraint of pressure and temperature, which is not possible in shock experiments. It is the closest study to timescales suggested by the meteorites found to date. Calibration of the plagioclase phase diagram in terms of strain rate and timescale could produce a more accurate compositional analysis of various meteorites/craters and a better picture of the impact events that created them.  The series of experiments primarily represent a necessary building block towards experiments on realistic timescales for melt veins and impact centers; essentially simulating meteorite impacts in the diamond anvil cell.

Biography:  Melissa is a third year geoscience PhD candidate, originally from South Carolina. She attended the College of Charleston, where she earned a BA in physics, and the University of South Carolina, where she earned a BS in geophysics. At USC, Melissa processed seismic data for the Earth Sciences and Resources Institute’s $10 million DOE Carbon Sequestration Project for geologic characterization of the South Georgia Rift basin for source proximal CO2 storage. She completed a MS in geosciences through the “Career Path for African-American Students from HBCUs to National Laboratories” program here at Stony Brook. Melissa decided to stay at Stony Brook for the PhD program. In her first year, Melissa was chosen to Introduce of Department of Energy Secretary Ernest Moniz at the Brookhaven National Lab Commencement Ceremony. Melissa works in mineral physics and planetary science in Dr. Lars Ehm's group. She is a Turner, Bridge to the Doctorate and AGEP-T Fellow.


 Tuesday, October 11, 2016 at 12:30 PM



Login to Edit