HR: 0800h
AN: GP11A-0822    [Abstracts]
TI: Electronic Charge Carriers in Igneous Rocks and their Activation by Stress
AU: * Takeuchi, A
EM: takeuchi@science.sjsu.edu
AF: NASA Goddard Space Flight Center, Geodynamics Branch MS 921, Greenbelt, MD 20771 United States
AU: * Takeuchi, A
EM: takeuchi@science.sjsu.edu
AF: San Jose State University, Department of Physics, San Jose, CA 95192-0106 United States
AU: Lau, B W
EM: blau@science.sjsu.edu
AF: NASA Goddard Space Flight Center, Geodynamics Branch MS 921, Greenbelt, MD 20771 United States
AU: Lau, B W
EM: blau@science.sjsu.edu
AF: San Jose State University, Department of Physics, San Jose, CA 95192-0106 United States
AU: Freund, F
EM: ffreund@core2.gsfc.nasa.gov
AF: NASA Goddard Space Flight Center, Geodynamics Branch MS 921, Greenbelt, MD 20771 United States
AU: Freund, F
EM: ffreund@core2.gsfc.nasa.gov
AF: San Jose State University, Department of Physics, San Jose, CA 95192-0106 United States
AU: Freund, F
EM: ffreund@core2.gsfc.nasa.gov
AF: NASA Ames Research Center, Earth System Science and Technology, MS 242-4, Moffett Field, CA 94035-1000 United States
AB: The electrical conductivity of the crust does not only depend on saline fluids in interconnected pores, conductive mineral phases such as sulfides, graphite, and/or intergranular carbon films. Igneous and high-grade metamorphic rocks also possess an intrinsic electrical conductivity, which can make an important contribution. This conductivity is electronic in nature and p-type due to the presence of defect electrons (holes) as mobile charge carriers. To study this conductivity, we subject the inner portion (7.5 cm diameter) of thin slabs of air-dry granite and anorthosite (30 x 30 x 0.95 cm$^{3}$) to uniaxial stress with and without applying dc voltages. With a dc voltage applied, we measure currents through the rocks that indicate a substantial intrinsic conductivity. Upon applying a load we measure additional currents that flow (i) through the stressed rock and (ii) through the surrounding unstressed rock. Igneous and high-grade metamorphic rocks contain positive hole pairs (PHP), O$_{3}$X-OO-XO$_{3}$ with X = Si$^{4+}$, Al$^{3+}$ etc. According to our data stress activates these defects, thereby generating positive holes. These represent defect electrons in the valence bands of the otherwise insulating materials. Similar currents or conductivity changes are expected to be activated in the crust during the build-up of tectonic stresses, for instance before earthquakes.
DE: 8045 Role of fluids
DE: 8145 Physics of magma and magma bodies
DE: 5109 Magnetic and electrical properties
DE: 5194 Instruments and techniques
DE: 1645 Solid Earth
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2004 AGU Fall Meeting