DISTRIBUTION OF L- AND L-S TECTONITE IN THE OLIVER HILL DOME, EASTERN ADIRONDACK MOUNTAINS, NEW YORK

The Adirondack mountains of NY State are underlain by Proterozoic rocks that are cross-cut by numerous large ductile shear zones. These shear zones contain a wide range of fabrics including L-, L-S and S-tectonites. Although these fabrics have been described by earlier workers, the distribution of intensity variation within specific ductile shear zones has only been documented locally. During this study we examined, in detail, the distribution of these fabrics within a shallowly dipping ductile shear zone that occurs in the area north of Olmsteadville, NY, at Oliver Hill and Green Mountain. Penetrative foliation occurs in granitic- and charnockitic-gneiss. This foliation is defined by planar aggregates of quartz and feldspars, with accessory biotite, hornblende, and occasional clinopyroxene. The foliation defines a broad open dome, but at the scale of kilometers, the foliation is highly variable in attitude. Although mineral lineations occur in all rocks of this region, they are best developed on the southern flank of the Oliver Hill dome, where a 1.5 km wide zone of L>>S tectonite occurs. Lineations are defined by rod-shaped aggregates of dynamically recrystallized quartz and feldspars, and accessory mafic phases. The lineations have a trend that ranges from 080 to 125, with the maximum trend at 110. The plunge is generally shallow, with an average of 09 eastward. The meta-igneous rocks occur structurally above a sequence of deformed meta-sedimentary rocks including marble, phlogopite-schist, pelitic- and psammitic-gneiss, all interlayered at the scale of meters to 10’s of meters. Kinematic analysis was performed on rocks containing L-S fabrics. Type I S-C, sigma- and delta-porphyroclasts, and shear bands were all observed, and the shear sense is consistently top toward the west. These data suggest that the meta-igneous rocks were thrust westward over the meta-sedimentary rocks in this part of the Adirondacks.