KINEMATIC ANALYSIS OF THE PISECO ANTIFORM ALONG THE SACANDAGA RIVER TRANSECT, SOUTHEASTERN ADIRONDACKS, NEW YORK

The Piseco Lake shear zone is a major Ottawan age structure that crosses the southern Adirondacks from west to east. Detailed kinematic study of the shear zone has primarily been done in the region of the type-locality near Piseco Lake, and westward to the margin of the Adirondack massif near Hinckley Reservoir. At the type location, the Piseco Lake zone is divided into two domains: a steep mylonite zone in the south that is flanked by an asymmetric foliation dome in the north. Within the Sacandaga River transect, located about 80 km east of Piseco Lake, the antiform was mapped by earlier researchers. The core contains L-tectonite that transitions into L-S tectonite on the N and S limbs. It was reported that feldspars with slightly asymmetric tails and S-C fabrics suggest a component of NW directed thrusting. Finally, a polyphase fold history was employed to explain outcrop fabrics and the map-scale distribution of lithologies.

During this study, a detailed macro- and micro-structural analysis was undertaken along the Sacandaga River transect to understand the kinematic history. Oriented samples and structural field data were collected from all the outcrops located between Wells and Northville, NY. The foliation attitude varies and defines the foliation arch of the Piseco antiform. Mineral elongation lineations are consistently subhorizontal and trend ~110. Each sample was cut to reveal mutually perpendicular rock faces oriented 1) parallel to S and L, 2) perpendicular to S and L, and 3) perpendicular to S and parallel to L. Every sample contains excellent macroscopic kinematic indicators such as sigma and delta grain-tail complexes, and/or Type I S-C foliations. Rocks from the antiform north limb reveal low-angle shear parallel to the lineation with top to the west displacement. Rocks form the south limb also reveal low angle shear parallel to the lineation with top to the east displacement. The core of the antiform is dominated by L-tectonite, and the lack of a macroscopic foliation hampered shear sense analysis. Considering the mineral elongation lineations are subhorizontal, the north and south limbs of the Piseco antiform along the Sacandaga River transect experienced sinistral shear. This is consistent with the shear sense that was reported for the Piseco Lake region, and suggests that the Piseco antiform developed in a sinistral shear couple.