THE MOOSE RIVER PLAIN SHEAR ZONE, CENTRAL ADIRONDACKS, NY

The Moose River Plain shear zone (MRPz) contains high-grade mylonitic rock that traces E-W through the Moose River plain in the western Adirondacks, NY. Shear zone foliation dips 30-65 degrees north, strikes E-W, and is developed in felsic, pelitic and mafic gneisses. Mineral lineations trend E-W and are defined by linear aggregates of felspar & pyroxene in felsic & mafic rocks, and streaks of biotite & sillimanite, & elongate garnets in pelitic rocks. The eastern trace of the MRPz intersects the Snowy Mt. dome (SMD) while the western extent of the zone still needs to be delineated. Kinematic analysis along the length of the MRPz revealed shear sense of top toward the west. Along the main segment, kinematic indicators such as S-C fabrics, garnet-fish, asymmetric folds & foliation boudins, & sigma & delta-clasts all show strike-parallel shear with the hangingwall displacement westward. Where the MRPz traces into the SMD, the dip direction progressively changes from N to W, lineations plunge shallowly west, & the shear sense is still top toward the west. In the region west of Cellar Mt., the trace of the MRPz bends toward the southwest about 30 degrees, and then back westward over a distance of 5-6 km. In this part of the zone, shear bands and asymmetric foliation boundin with small granite pods indicate minor strike-parallel extension. Taking into account the strike-parallel shear sense of the main zone and the local extension where the MRPz is bent, the map-scale kink in the zone has the geometry of a sinistral releasing bend. Regionally, the MRPz occurs between the Wakely Mt. antiform and the Little Moose Mt. synform, & probably accommodated differential shear between these large folds. The vergence of these folds, as deduced from the map pattern, is consistent with the shear sense documented along the MRPz.