USING TEXTURAL AND EBSD DATA TO CHARACTERIZE STRAIN AND KINEMATIC VARIATIONS WITHIN THE CHUNKY GAL MOUNTAIN FAULT, SOUTHERN APPALACHIAN BLUE RIDGE PROVINCE, NORTH CAROLINA

In its type exposure, the terrane-bounding Chunky Gal Mountain Fault separates strongly foliated amphibolite from biotite paragneiss. The fault zone includes several NE-trending, steeply SE dipping ~ 1m wide mylonitic shear zones with apparent normal movement suggested by deflected foliation. Lineation orientations and shear sense from kinematic indicators vary within the zones, including steep lineations with normal kinematics and shallow NE-plunging lineations with either dextral or sinistral movement. Detailed strain and kinematic analysis is critical to understanding this complex fault zone.

We focus here on a sample suite of Grt-Bt gneisses within shear zone ‘L’ for which we have constraints on timing and metamorphic conditions of movement. All shear zone ‘L’ samples possess a shallow elongation lineation. L6 from the shear zone center is typical of the mylonites and preserves sinistral kinematics. L3 (sinistral) and L4 (dextral) are ultramylonites from the SE and NW margins, respectively. L7 is a protomylonite (dextral), collected several cm NW of the shear zone.

Quartz is extensively recrystallized; some larger grains contain subgrains and/or are flattened oblique to foliation. Quartz microstructures are mostly typical of regime 3 dislocation creep or transitional from regime 2 to 3 in lower strain domains. Quartz ribbon width varies from 0.05 mm in ultramylonite up to ~1 mm in lower strain domains. Feldspar porphyroclasts display undulose extinction and subgrain development with local fine recrystallization along some margins and tails. Textural variations appear to reflect differences in strain (e.g. ultramylonite – protomylonite) rather than kinematics.

Quartz CPO measured in several domains per sample using EBSD display asymmetry consistent with textural kinematic interpretations. Quartz c-axis orientations vary from cross girdle to single girdle patterns with increasing strain. Maxima near Z are consistent with basal <a> and rhomb <a> slip. CPO patterns are consistent with regime 3 dislocation creep. Cross girdle patterns suggest a significant component of pure shear in all but the highest strain domains. Our observations suggest that deformation took place at relatively high temperatures (>5-600^oC) and samples with opposite kinematics deformed under similar deformation conditions.