DEFORMED KYANITE: ORIGIN AND SIGNIFICANCE IN THE RAFT RIVER CORE COMPLEX OF UTAH

Deformed kyanite-quartz veins in the Miocene detachment fault zone of the Raft River metamorphic core complex, Utah, may provide information about P-T-fluid-deformation conditions prior to or during core complex development. In the field, boudinaged 2-50 cm thick kyanite-quartz veins are hosted in a distinctive muscovite-rich quartzite horizon and can be followed over 4 km along Clear Creek. Deformation of kyanite and quartz is also observed at the microstructural scale: although some kyanite appears undeformed, many crystals are kinked or folded. Samples of the vein consist of primarily quartz (~50%) and kyanite (~45%), but contain significant rutile (~2%) and trace tourmaline and zircon. Most quartz grains are <1mm but some are as large as 3-10mm; most kyanite grains are around 0.25 mm. Kyanite, quartz and rutile were confirmed with electron backscatter diffraction (EBSD) and zircon with EDS analyses.

EBSD analysis of a bent kyanite crystal shows no internal grain boundaries with misorientations of >10°, but a consistent orientation shift along the 0.950 mm crystal producing a cumulative misorientation of 45° between the extremes of the crystal. EBSD analysis of a kinked kyanite displayed seven different orientation bands across the length of the 0.5 mm crystal. Misorentation between the bands ranges from 17° to 50° across the kink band boundaries. A pole figure from the kinked crystal displays a dense uniform point for the <010> pole, but the orientation of the <100>, and <001> axes are smeared, indicating rotation around the <010> pole. Rotation about <010> is consistent with the known easy glide system. Future work will involve determination of the quartz fabric with EBSD and stable oxygen isotope analysis of quartz, kyanite, muscovite, and rutile in the veins to determine the temperature at which these minerals equilibrated during deformation. Results will be compared for consistency with quartz-muscovite stable isotope thermometry from the rest of the section.