HR: 1340h
AN: V43A-1549    [Abstracts]
TI: Kyanite deformation in whiteschist of the UHPM Kokchetav Massif, Kazakhstan
AU: * Beane, R J
EM: rbeane@bowdoin.edu
AF: Bowdoin College, 6800 COllege Station, Brunswick, Me 04011 United States
AB: Microstructures of ultrahigh-pressure metamorphic (UHPM) rocks can provide information on metamorphic and deformation conditions in subduction zones. Kink-banded kyanite in whiteschist from the Kokchetav Massif displays evidence for crystal plastic deformation. The whiteschist, associated with eclogite lenses, is part of UHPM Unit II located south-west of Lake Zheltau in the Kulet region. Equilibrium assemblage is Ky+Grt+Tlc+Phe+Coe/Qtz. Previously reported peak P-T conditions are approximately 3.5GPa at 750C. Strong foliation is defined by Tlc+Phe, with a corresponding, but weaker, preferred orientation of Ky. Crystallographic orientation maps and analyses of Ky blades and inclusions were preformed using electron backscatter diffraction (EBSD) methods. Kyanite blades, up to 10 mm in length, exhibit rotations at kink bands of 10-30 degrees about [010], defining a glide plane of (100). Kyanite inclusions surrounded by Tlc in extensively fractured garnets are 100-500um in diameter, not kink-banded, and with only minor misorientations at the edge of the inclusions. Kink-banding and crystal plastic deformation of kyanite blades is interpreted to have occurred during exhumation to mid-crustal levels because associated quartz grains are optically unstrained and kyanite inclusions in garnet lack evidence for deformation. Further EBSD studies of Omp, Ky, Grt and exsolution phases in UHPM rocks have the potential to lend further insights into subduction zone processes and exhumation mechanisms.
DE: 3613 Subduction zone processes (1031, 3060, 8170, 8413)
DE: 3625 Petrography, microstructures, and textures
DE: 3654 Ultra-high pressure metamorphism
DE: 3660 Metamorphic petrology
DE: 8413 Subduction zone processes (1031, 3060, 3613, 8170)
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005