Mineral Physics Institute Summer Scholars Program

Lisandra Rosario Universidad Metropolitana, Puerto Rico Major: Chemistry Mentors: Jiuhua Chen

Summer Project Description:

Title: Study of rheological behavior of olivine, pyroxene and their mixture at high pressure

Rheological properties of mineral is crucial to understanding mantle dynamics such as convection and earthquakes that happen
in the Earth's deep interior. This project is to study rheological behavior of olivine (Mg,Fe)2SiO4, pyroxene (Mg,Fe)2SiO3 and their
mixture. While olivine has been extensively studied, pyroxene and mixture of olivine and pyroxene are much less studied, especially
the mixture. When two materials mixed together, rheological property of the aggregate might not simply be an average of the two
individual materials. This is particular important for understanding the Earth's interior as it consists of more than one dominant minerals.
Olivine and pyroxene are believed to be the two dominants minerals in the upper mantle.

Conducting deformation experiments using synchrotron x-rays at high pressure and temperature to measure the stress and
strain of minerals we can study their rheological properties. The experiment technique for in situ stress and strain measurements
has been developed at the X17B beamline of the NSLS. The sample is loaded into a boron: epoxy cubic pressure medium,
between two hard corundum pistons. A gold foils placed between the sample and the piston at each end as strain mark. The sample
is first compressed at room temperature and then heated to high temperature. To get the strain the sample length is measured directly
from the distance between two strain marks at each side of the sample on the X-ray radiograph image of the high pressure cell.
The stress is measured by simultaneously collecting energy-dispersive X-ray diffraction patterns of the sample in two perpendicular
diffraction planes. Differential stress in the sample is derived from the different lattice strains along the different orientations relative to
principal stress direction. Combining the information obtained from these two analyzing processes we can understand the rheology-flow
properties of the sample.