THE INDIAN LAKE FAULT ZONE AND SNOWY MOUNTAIN DOME, CENTRAL ADIRONDACK MOUNTAINS, NEW YORK

A number of northeast trending lineaments transect the Adirondack Mountains of New York, and are interpreted to be fault zones. One such lineament traces through the Piseco and Indian Lake regions, and then follows the drainage of the upper Hudson River, a distance of more 70 km. This lineament crosses the Snowy Mt. dome in the area of Indian Lake. A field study was conducted in the central and southern extent of Indian Lake, and on the eastern flank of Snowy Mt. dome to: 1) produce a structure map across the lineament; 2) document any on-ground deformation features associated with the lineament; 3) determined the eastern extent and geometry of the dome; and 4) assess the kinematic history of the Indian Lake fault zone using large-scale structure. The structure maps from the lake region reveal a dominant set of subvertical, 210-240 striking, fractures zones with fracture density >12 per meter. Within charnockitic gneiss, these fracture zones contain anastomosing fractures, the zones are upward of a few meters wide, and sometimes contain gouge. The gouge consists of broken primary grains of feldspar and quartz. Moderately common gash fractures occur within these zones, with most containing quartz and minor chlorite. Away from Indian Lake, mineralized fractures with the same orientation also exist, but the intensity of fracturing is much higher in the lake region. The Snowy Mt. dome is defined by penetrative foliation in gabbroic- and charnockitic-gneisses, that mantle a core of variably deformed anorthosite. The dome is flanked by a suite of metasedimentary rocks containing quartzite, marble, calcsilicate- and pelitic- gneiss and occasional amphibolite. Detailed geologic mapping east of Indian Lake revealed no obvious structural discontinuity across the Indian Lake lineament, except that the metasedimentary rocks occur at a structural level consistent with vertical displacement. Palinspastic reconstruction of the Snowy Mt. dome, suggests that the Indian fault zone may have experienced as much as 2000 meters of vertical displacement with the southeastern block down.