HR: 15:20h
AN: V23C-06    [Abstracts]
TI: Synchrotron Radiation Study of the Kinetics of Dehydration of Chrysotile Fiber
AU: * Earnest, D J
EM: earnest@glue.umd.edu
AF: Laboratory for Mineral Deposits Research, Department of Geology, University of Maryland, College Park, MD 20742 United States
AU: Candela, P A
EM: candela@geol.umd.edu
AF: Laboratory for Mineral Deposits Research, Department of Geology, University of Maryland, College Park, MD 20742 United States
AU: Wylie, A G
EM: wylie@deans.umd.edu
AF: Laboratory for Mineral Deposits Research, Department of Geology, University of Maryland, College Park, MD 20742 United States
AU: Crummett, C D
EM: crummett@geol.umd.edu
AF: Laboratory for Mineral Deposits Research, Department of Geology, University of Maryland, College Park, MD 20742 United States
AU: Frank, M R
AF: Department of Geology and Environmental Geosciences, Northern Illinois University, Illinois, IL 11111 United States
AB: Chrysotile fiber from the Thetford region of Quebec in Canada was heated in hydrothermal diamond anvil cells (HDACs) under both hydrothermal and atmospheric pressure conditions. Temperatures between 25\deg\ C and $>$800\deg\ C were attained at varying rates using electrical resistance heating elements surrounding the sample space. The HDACs were fixed in the path of a synchrotron-radiation beam at the Advanced Photon Source (APS) at the Argonne National Laboratory. X-ray diffraction patterns were recorded with high temporal resolution in order to develop time-temperature transformation curves for the decomposition of chrysotile and subsequent formation of crystalline phases such as forsterite, tridymite, talc, and amphibole. During atmospheric-pressure experimentation chrysotile was confined in sample space drilled in rhenium-foil gasket material ranging in thickness between 150-300 microns. Diamond anvils were brought into light contact with the gasket material and no further pressure was applied. For hydrothermal experimentation, rhenium-foil gaskets were loaded with chrysotile and pure water, and pressure measurement utilized pressure-temperature-density diagrams calculated from an equation of state for water. During 72 hours of experimentation at APS approximately 150 diffraction patterns were generated under a variety of temperature/time/pressure conditions. Following are some of the significant results obtained: On rapid heating at atmospheric pressure from 120\deg\ C to 800\deg\ C ($<$3 minutes) chrysotile is more than 90% decomposed, and the growth of forsterite, tridymite, and talc are noted. At 32 minutes with the temperature held at 800\deg C chrysotile is absent and forsterite, tridymite and talc phases are growing. At 103 minutes talc is absent and an 8.3\AA\ peak consistent with amphibole growth appears, while tridymite abundance is decreasing. At 164 minutes forsterite and amphibole are increasing in abundance and tridymite continues to decrease. At 280 minutes tridymite is absent while forsterite and amphibole remain. Notable is the transient state of coexistence of forsterite and tridymite for more than 164 minutes but less than 280 minutes. Investigation of lower temperature reactions exhibited a destabilization of the chrysotile structure at 450\deg\ C after 240 minutes, seen as loss of peak area for major chrysotile d-spacings, accompanied by formation of a number of peaks in the 1.3-3\AA\ range of d-spacing. Chrysotile that was held off-line at 450\deg\ C and at atmospheric pressure for 48 hours revealed a well-developed diffraction pattern consistent with growth of forsterite. Ongoing analysis of the data collected at APS will help define a kinetic framework for the dehydration and decomposition of chrysotile, and help to refine the experimental design for future studies. Additionally, integration of these data with data from our limited hydrothermal experimentation will expand our understanding of the role hydrothermal fluids play in rates of decomposition.
DE: 3630 Experimental mineralogy and petrology
DE: 3660 Metamorphic petrology
DE: 3694 Instruments and techniques
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting