KINEMATIC HISTORY OF THE CLARE MYLONITE IN THE NORTHWEST ADIRONDACKS: STRUCTURAL AND PETROGRAPHIC ANALYSIS

Shear zones in the northwest Adirondacks remain enigmatic in terms of the kinematic history. Mylonites are ubiquitous throughout the northwest Adirondacks and much attention has been given to the Carthage Colton shear zone (CCsz) as the boundary between the Adirondack Highlands and the Adirondack Lowlands. Although there are many recent geochronology studies, there are few published structural studies with systematic strain analysis at the meso- and microscales. The Clare shear zone (Clare Fault) is mapped as a distinct structure in the Adirondack Highlands separate from the CCsz. The mylonite zone, well exposed at a road cut at Brouse’s corner, has been previously described as an extensional feature, and geochronology of an associated pegmatite has been dated at 1044 ± 7 Ma (Selleck et al., 2005). The 63-meter exposure is dominated by leucogranitic gneiss and includes a 2-meter zone of mylonite. The dominant foliation of the gneiss and the mylonite strikes roughly E-W and dips moderately to the N. Detailed field work and microstructural analyses of the Clare shear zone indicates a complicated kinematic history including a dominant strike-slip component in addition to the previously recognized sense of normal (top down to the NW) motion on the shear zone. A combination of analog (Bruntons and field books) and digital (iPads and iPhones) tools were used to conduct fieldwork. Data was compiled in the field using StraboSpot, a new structural geology application that enables a variety of data at multiple scales to be integrated into one project. Seven oriented samples were collected within and surrounding the mylonite and orthogonal sections were cut to enable quantification of strain in 3 dimensions.