HR: 14:40h
AN: T43E-05    [Abstracts]
TI: Experimental Investigation of the Dissolution of Quartz by Muscovite Mica Surfaces: Implications for Pressure Solution
AU: * Greene, G W
EM: wren@umail.ucsb.edu
AF: Department Of Materials, University of California, Santa Barbara, CA 93106-5050,
AU: Kristiansen, K
EM: kai@engineering.ucsb.edu
AF: Department of Chemical Engineering, University of California, Santa Barbara, CA 93106- 5050,
AU: Meyer, E
EM: emmo@engineering.ucsb.edu
AF: Department of Chemical Engineering, University of California, Santa Barbara, CA 93106- 5050,
AU: Boles, J
EM: boles@geol.ucsb.edu
AF: Department of Earth Sciences, University of California, Santa Barbara, CA 93106-5050,
AU: Israelachvili, J
EM: jacob@engineering.ucsb.edu
AF: Department of Chemical Engineering, University of California, Santa Barbara, CA 93106- 5050,
AB: Using the Surface Force Apparatus, which gives angstrom resolution of thin film and water layer thicknesses, we have measured dissolution of quartz sheets when muscovite mica surfaces are pressed against them in aqueous electrolyte solutions of CaCl2 (30 mM) at relatively low pressures (2-3 atm) and temperatures (25 °C). No detectable dissolution occurs in symmetrical systems (e.g. mica-mica or quartz-quartz) or in dry cases under similar pressures, indicating that the dissolution phenomena can not be attributed to simple pressure effects, slow aging effects, or plastic deformation of the quartz surface. In quartz-mica systems under pressure and in electrolyte solution, the onset of quartz dissolution is marked by a sudden, rapid, and spontaneous change in the quartz thickness. Upon the onset of quartz dissolution, we measure initial dissolution rates that range from 1 to 4 nm/min that gradually settle after several hours into a constant rate that is approximately 0.01 nm/min. The change in decay rate is interpreted as the gradual transformation of the quartz surface from an ordered crystalline lattice into a more amorphous and porous structure as material is removed by the dissolution process in a manner analogous to corrosion. We believe that the pressure solution is an electro-chemical phenomena driven by the electrostatic potential generated when two surfaces possessing dissimilar surface charge potentials are forced into close proximity in the presence of an electrolyte. We have measured up to 150 mV between quartz mica surfaces at the above conditions, confirming the presence of a electrical potential. Recent experiments examining dissolution in multi-faceted milled quartz particles (~ 1.0 μm diameter) compressed between two muscovite surfaces reveal a dissolution driven evolution of the particle geometry that suggests an asymmetry in the dissolution rates at different crystallographic planes. Dissimilarities in the surface charge potentials of different crystallographic planes and resultant differences in dissolution could give rise to the irregular patterns characteristic of stylolites in micaceous sandstones.
DE: 3947 Surfaces and interfaces
DE: 8194 Instruments and techniques
SC: Tectonophysics [T]
MN: 2007 Fall Meeting