Date of Last Revision
2023-05-02 23:40:29
Major
Geology
Degree Name
Bachelor of Science
Date of Expected Graduation
Spring 2017
Abstract
Intermediate depth (170-400 km) deep focus earthquakes are observed in subducting slabs, but unlike shallow (50-170 km) and deep (400-660 km) deep focus earthquakes, the mechanism(s) responsible for them are not clear. Two common alteration products observed in peridotites, magnesite and dolomite, are stable along the pressure-temperature path of a subducting slab. Low pressure experiments indicate that these minerals are weaker than olivine, but there are no data about the pressure dependence of the strength of magnesite or dolomite. Magnesite and dolomite cylinders (1mm by 1mm) were deformed in stacked series to 25-30% strain using the deformation-DIA (DDIA) at Argonne National Lab at 500°C and three different pressures of 3.1 GPa, 5.8 GPa, and 6.2 GPa. In order to determine the pressure dependence of magnesite and dolomite deformed by low temperature plasticity, stacked samples allow direct observation of the materials’ relative strengths via differences in strain rates. At all conditions, dolomite deformed at a constant strain rate, which does not evolve with increasing strain. However, magnesite strain weakened during all experiments. Magnesite is initially isoviscous or stronger than dolomite, but with increasing strain, became weaker than dolomite. These results indicate that presence of magnesite in subduction zones can cause strain localization and therefore be the likely source of intermediate depth deep focus earthquakes.
Research Sponsor
Dr. Caleb Holyoke
First Reader
Dr. John Peck
Second Reader
Dr. Meagan Ankney
Recommended Citation
Blasko, Cole, "Pressure Dependence of Polycrystalline Magnesite and Dolomite" (2017). Williams Honors College, Honors Research Projects. 462.
https://ideaexchange.uakron.edu/honors_research_projects/462