Dr. Janelle Homburg has been awarded an NSF Earth Science Postdoctoral Fellowship to carry out a research and education plan at the University of Minnesota. This work will investigate the effects of mineralogical composition (olivine/pyroxene modal abundance), water content and pressure on the strength of Earth's upper mantle in order to better understand large-scale dynamic mantle processes. To this end, an important goal of this study is to utilize experimental work to develop flow laws (relationships between stress and strain rate) that incorporate the effects of composition, water and pressure.
Experiments will be preformed on olivine/pyroxene aggregates ("harzburgite" rocks) utilizing the D-DIA, a high-pressure deformation apparatus. The recent development of the D-DIA will allow this study to investigate high-pressure conditions (3-12 GPa) that have previously been unobtainable in the lab and are more representative of deformation conditions throughout the upper mantle. In addition to analyzing the mechanical data from each experiment, the run products will be analyzed by a number of different techniques (infrared spectroscopy, electron backscatter diffraction, and transmission electron microscopy) in order to develop a deeper understanding of the microphysical processes involved in deformation.
While the mechanical behavior of the shallow Earth is thought to be relatively well understood, great uncertainty still remains in the deformation behavior of the deeper portion of the upper mantle (depths greater then ~100 km). This situation is due in large part to the fact that prior to the advent of the D-DIA, the range of pressures accessible in the lab was fairly limited. The series of experiments planned in this research will allow for better understanding of the deformation behavior of earth materials throughout the entire upper mantle and, by extension, better understanding of a wide variety of key geodynamic processes, such as subduction.
In addition to developing J. Homburg's skills as a researcher, this fellowship will allow her to develop as an educator both in classroom and outreach settings. She will assist in teaching geology courses and in mentoring undergraduate and graduate students at the University of Minnesota. She will also be involved in the development of science education programs at the Science Museum of Minnesota.
This work investigated the effects of mineralogical composition (olivine/pyroxene modal abundance), water content and pressure on the strength of Earth’s upper mantle in order to better understand large-scale dynamic mantle processes. To this end, an important goal of this study was to utilize experimental work to develop flow laws (relationships between stress and strain rate) that incorporate the effects of composition, water and pressure. Experiments have been preformed on olivine/pyroxene mixtures ("harzburgite" rocks) utilizing the D-DIA, a high-pressure deformation apparatus. These experiments were conducted under both wet and dry conditions to simulate the wide rage of natural conditions found in the earth. The recent development of the D-DIA allowed this study to investigate high-pressure conditions (3-12 GPa) that have previously been unobtainable in the lab and are more representative of deformation conditions throughout the upper mantle. The mechanical data from these tests was evaluated and it was found that pyroxene and olivine:pyroxene mixtures are weaker than olivine under the conditions that were examined. Additionally, olivine:pyroxene mixtures appear to be weaker than either end member. The introduction of water also appears to weaken the system. However these conclusions are still quite early and more work will need to be done to quantify these affects. While the mechanical behavior of the shallow Earth is thought to be relatively well understood, great uncertainty still remains in the deformation behavior of the deeper portion of the upper mantle (depths greater then ~100 km). This situation is due in large part to the fact that prior to the advent of the D-DIA, the range of pressures accessible in the lab was fairly limited. The series of experiments planned in this research allowed for a better understanding of the deformation behavior of earth materials throughout the entire upper mantle and, by extension, better understanding of a wide variety of key geodynamic processes, such as subduction. In addition to developing J. Homburg’s skills as a researcher, this fellowship allowed her to develop as an educator. She assisted in mentoring undergraduate and graduate students at the University of Minnesota and contributed to several graduate level seminars.
