HR: 11:55h
AN: V22B-07    [Abstracts]
TI: Serpentine dehydration kinetics up to 1023 K and 4 GPa
AU: * Frank, M R
EM: mfrank@niu.edu
AF: Department of Geology and Environmental Geosciences, Davis Hall, Northern Illinois University, DeKalb, IL 60115, United States
AU: Scott, H P
EM: hpscott@iusb.edu
AF: Department of Physics and Astronomy, Indiana University, South Bend, South Bend, IN 46634, United States
AU: Maglio, S
EM: stevemaglio@gmail.com
AF: Department of Geology and Environmental Geosciences, Davis Hall, Northern Illinois University, DeKalb, IL 60115, United States
AU: Aarestad, B
EM: aareth2000@yahoo.com
AF: Department of Geology and Environmental Geosciences, Davis Hall, Northern Illinois University, DeKalb, IL 60115, United States
AU: Uesugi, J
EM: jyu100@hotmail.com
AF: Department of Geology and Environmental Geosciences, Davis Hall, Northern Illinois University, DeKalb, IL 60115, United States
AU: Prakapenka, V
EM: prakapenka@cars.uchicago.edu
AF: Center for Advanced Radiation Sources, University of Chicago, Argonne, IL 60439, United States
AB: Serpentine minerals are ubiquitous within the oceanic lithosphere and are hypothesized to be a significant source of water, released during thermal dehydration, in subduction zones. Additionally, serpentinized oceanic mantle has been hypothesized to represent a fluid and incompatiable element reservoir that could be a major part of element cycling in subduction zones. Data detailing the kinetics of serpentine breakdown are difficult to obtain and require in situ analyses. Candela et al., 2007 ( Am. Min., In Press) and Frank et al., 2005 ( GSA Abs. Programs) illustrated that the breakdown of serpentine minerals (chrysotile and lizardite, respectively) is complex and results in the variable release of H₂O. Further, it has been noted that the reaction products proceed in a step-wise fashion as a function of temperature and these ‘‘steps'' are not the same for all serpentine minerals. In order to understand the release of volatile phases from serpentine minerals in subduction zones, we studied the thermal decomposition of lizardite over a range of temperature, 500- 750°C in 25° increments, at atmospheric pressure. High-pressure experiments ranged from 2-5 GPa and were conducted from 550-700°C. The thermal decomposition of lizardite was monitored by using a hydrothermal diamond anvil cell and synchrotron X-ray radiation. The experiments were conducted at the GSECARS 13-BM-D beam line (Advanced Photon Source at Argonne National Laboratory), using monochromatic X-ray radiation, with a wavelength of 0.3344 Å, and a MAR 345 online imaging system. The diffraction data were used to monitor the dehydration reactants and products as a function of temperature and time. The reaction products of serpentine dehydration are dominantly forsterite (at all temperatures and pressure of dehydration) with minor amounts of talc-like and anthophyllite-like phases. Enstatite could not be identified definitively. Further, forsterite nucleates before more silica-rich phases, at generally lower temperatures and persists throughout the duration of the experiments, and at lower temperatures than have been reported previously in the bulk of the literature. Increasing temperature, at any given pressure, increased the rate of reaction up to complete dehydration of serpentine in less than five minutes at 700-750°C. Our results constrain the products of serpentine thermal decomposition and the potential mechanism of H₂O release within serpentine-rich subduction zones.
DE: 3610 Geochemical modeling (1009, 8410)
DE: 3612 Reactions and phase equilibria (1012, 8412)
DE: 3613 Subduction zone processes (1031, 3060, 8170, 8413)
DE: 3630 Experimental mineralogy and petrology
DE: 3924 High-pressure behavior
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting