HR: 14:25h
AN: T43D-04    [Abstracts]
TI: Inferring the kinetics of dynamic recrystallization from microstructural observations, with implications for the deformation of peridotite
AU: * Skemer, P
EM: philip.skemer@yale.edu
AF: Yale University Department of Geology and Geophysics, 210 Whitney Ave, New Haven, CT 06520, United States
AU: Karato, S
EM: shun-ichiro.karato@yale.edu
AF: Yale University Department of Geology and Geophysics, 210 Whitney Ave, New Haven, CT 06520, United States
AB: The processes of dynamic recrystallization have important influences on the deformation of rocks. We have revisited sheared-lherzolite xenoliths using modern SEM-based analytical techniques. In this manner, we demonstrate that olivine and orthopyroxene recrystallized grains deformed by different deformation mechanisms. There are two additional contrasting features of the olivine and orthopyroxene deformation microstructures: First, the olivine recrystallized grain-size is at least a factor of five larger than the orthopyroxene recrystallized grain size. Second, the olivine recrystallization is complete, whereas the orthopyroxene recrystallization is only partially complete. To understand the origin of these differences, we have employed the Avrami theory of phase transitions (or recrystallization). In this theory, two observable parameters, i.e., grain-size (the Avrami length) and the characteristic time for recrystallization (the Avrami time) are expressed in terms of two microscopic parameters, i.e., the nucleation and the growth rate. We determined the nucleation and growth rates for olivine and orthopyroxene from the observed grain-size and the inferred characteristic time for recrystallization. The results indicate that the both the nucleation and growth rates in orthopyroxene are slower than those of olivine, although the difference in growth rate is much larger. We interpret the large contrast in growth rates to be a consequence of impurity atoms segregated to grain-boundaries of orthopyroxene, as demonstrated by the experimental study of Skemer and Karato (2007). The inferred sluggish kinetics of grain-boundary migration in orthopyroxene will help maintain the small grain-size of orthopyroxene, making it possible for orthopyroxene to deform by grain-size sensitive creep for a geologically significant length of time.
DE: 3902 Creep and deformation
SC: Tectonophysics [T]
MN: 2007 Fall Meeting