QUANTIFYING THE KINEMATIC EVOLUTION OF THE SLIDE LAKE SHEAR ZONE, SAWATCH RANGE, COLORADO

The sub-horizontal Slide Lake shear zone (SLSZ), located in the central Sawatch Range of Colorado, is a component of a northeast-striking shear system that was periodically active during Paleo- to Mesoproterozoic deformation. The main feature of the SLSZ is a ~100-m-thick zone of deformed pegmatite, calc-silicate and biotite gneiss, and migmatite characterized by a well-developed, northeast-dipping foliation and a shallowly plunging stretching lineation. Localized mylonites and ultramylonites display macro- and micro- shear sense indicators, including shear bands, asymmetric tails on porphyroclasts, mica fish, and oblique grain shape fabric that record both top-to-the-NW and top-to-the-SE shear sense. Ultramylonite zones contain rigid feldspar porphyroclasts within a matrix of dynamically recrystallized and partially annealed quartz, interlayered with micaceous domains. SLSZ samples are ideal for quantifying the relative contributions of pure and simple shear using rigid porphyroclast methods. Results will be compared with the adjacent, sub-vertical Homestake shear zone (HSZ), which records deformation during the Yavapai orogeny (1.7 Ga) and regional transpression (1.4 Ga). Kinematic investigations indicate that the SLSZ accommodated a component of NW-directed crustal shortening associated with regional transpression during the assembly of Laurentia.