HR: 14:10h
AN: T43D-03    [Abstracts]
TI: Influence of Pre-existing LPO on Texture Development in Ultramafic Shear Zones
AU: * Newman, J
EM: newman@geo.tamu.edu
AF: Dept. Geology and Geophysics, Texas A&M University, College Station, TX 77843, United States
AU: Webber, C
EM: cwebber@geology.wisc.edu
AF: ExxonMobil Exploration Company, 233 Benmar Drive, Houston, TX 77060, United States
AU: Holyoke, C
EM: holyoke@geo.tamu.edu
AF: Dept. Geology and Geophysics, Texas A&M University, College Station, TX 77843, United States
AU: Little, T
EM: Tim.Little@vuw.ac.nz
AF: School of Earth Sciences, Victoria University P.O. Box 600, Wellington, 6000, New Zealand
AU: Tikoff, B
EM: basil@geology.wisc.edu
AF: Dept. of Geology and Geophysics, University of Wisconsin-Madison, Madison, WI 53706, United States
AB: The Red Hills ultramafic massif, the South Island, New Zealand, contains a suite of cm-scale shear zones composed of dunite, pyroxenite, and olivine websterite. The shear zones cross-cut banded dunite and harzburgite host rock. Offset along the shear zones was measured using displacement of distinct compositional layers in the host rock, and is interpreted to occur by dominantly simple shear. While these zones contain a different mineralogy that the host rocks, they contain microstructures that are similar to the host rock, including coarse grain sizes (>1 mm) and dominantly polygonal grains. The olivine lattice preferred orientation (LPO) in the host rocks is consistent with the (010)[100] slip system, known to be active at high-temperature, upper mantle conditions. Within the shear zones, the olivine LPO, when plotted relative to the shear zone foliation and lineation, suggests (010)[001] slip. The shear zone LPO is typically more poorly clustered than in host rock samples, and double maxima are observed in some samples, with the second maxima suggesting (010)[100] slip. Fourier transform infra-red spectroscopy analysis of the shear zone olivines indicates that they are not fluid-rich relative to the host rock. When olivine LPO from both host rocks and shear zone samples is plotted within the same (geographic) reference frame, it is apparent that the shear zone LPO retains evidence for the dominant LPO of the host rocks. We suggest that the LPO in the shear zone rocks developed as a result of reactivation of a pre-exiting fabric; the poorly clustered data and double maxima reflect the change during deformation along the shear zone. These rocks demonstrate the influence of pre-existing LPO on texture development during deformation and the need to consider the LPO of deformed rocks within different reference frames.
DE: 3902 Creep and deformation
DE: 5112 Microstructure
DE: 5120 Plasticity, diffusion, and creep
DE: 8012 High strain deformation zones
DE: 8160 Rheology: general (1236, 8032)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting