HR: 1340h
AN: V23A-1227    [Abstracts]
TI: Crystal Size Distribution of Periclase in Contact Metamorphic Marbles as Record of Fluid Infiltration
AU: * Mueller, T
EM: mullet@rpi.edu
AF: Earth and Environmental Sciences Rensselaer Polytechnic Institute, 110 8th Street Science Center, Troy, NY 12180, United States
AU: Baumgartner, L
EM: Lukas.Baumgartner@unil.ch
AF: Institut de Minéralogie et Géochimie Université de Lausanne, Batiment Anthropole, Lasaunne, VD 1015, Switzerland
AU: Foster, C T
EM: Tom-Foster@uiowa.edu
AF: Department of Geology University of Iowa, Townbridge Hall North Capital Street, Iowa City, IA 52242, United States
AU: Bowman, J
EM: Bowman@earth.utah.edu
AF: Department of Geology and Geophysics University of Utah, 135 South 1460 East Browning Building, Salt Lake City, UT 84112, United States
AB: Crystal size distributions (CSD) of periclase in contact metamorphic marbles are combined with geochemical and petrologic information to deduce the controls that acted on the periclase forming reaction. Data are presented for two profiles in a dolomite xenolith in mafic intrusive rocks at the Cima Uzza, southern Adamello massif (Italy).
Stable isotope data and the presence of a sharp periclase reaction front on hand specimen scale shows that the formation of periclase is the consequence of high temperature fluid infiltration. Stable isotope data show depletion for ¹³C and ¹⁸O in a narrow region (~40cm) near the igneous contact, whereas the periclase forming reaction front extends up to 4m into the host rock. The carbon and the oxygen front are located at the same place, which would require an X(CO₂) of 0.5, if the isotope fronts are interpreted using a standard infiltration model, even if modelled as the side of a front.
A similar amount of reaction progress, calculated from measured volume of periclase (corrected for retrograde brucite formation), was found over the entire profiles. Surprisingly, dolomite is still present as prograde leftovers in most samples demonstrating that reaction did not go to completion. The median grain size of periclase crystals remains constant over both profiles. Nevertheless, CSD\'{ } s flatten systematically, reflecting a larger proportion of bigger grains with increasing distance from the contact. We interpret variations in grain sizes to be the result of changing reaction affinities along an infiltration front flattened (dispersed) by diffusion/dispersion and kinetics. A numerical model is presented, based on the textural analyses and geochemistry data from the field, describing the dynamic nucleation and crystallization of periclase in this infiltration driven system.
DE: 3610 Geochemical modeling (1009, 8410)
DE: 3612 Reactions and phase equilibria (1012, 8412)
DE: 3653 Fluid flow
DE: 3660 Metamorphic petrology
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting