EARLY TO LATE CRETACEOUS UNROOFING IN THE SOUTHEASTERN ADIRONDACK MOUNTAINS AND LAKE CHAMPLAIN BASIN OF NEW YORK AND VERMONT BASED ON APATITE FISSION-TRACK ANALYSIS

Apatite fission-track (AFT) ages determined for two samples from prominent fault zones in the southeastern Adirondack Mountains confirm a published trend of Early to Late Cretaceous unroofing ages in this region. Samples from Split Rock Falls in the Boquet River fault zone and the McGregor fault zone near Wilton, NY yielded AFT ages of 102 and 107 Ma, respectively. Samples from Trout Lake and Star Lake in the Northwest Lowlands of the Adirondacks yielded significantly older AFT ages of 143 and 151 Ma, respectively. These AFT ages are consistent with published AFT ages from this region. Samples from Raquette Lake, 122 Ma, and Piseco Lake, 123 Ma, in the south central Adirondacks, and the Noses area along the Mohawk river, 138 Ma, also yielded older AFT ages than those determined for the southeastern region. In order to determine if the trend of ~80-100 Ma AFT ages extends across the Lake Champlain basin into Vermont, thirty samples have been collected along three transects from Burlington in the north to Bennington in the south. Preliminary AFT ages for three samples suggest a continuation of young AFT ages in western Vermont. A Cretaceous dike from West Rutland and a Precambrian gneiss from Walker Mt. yielded AFT ages of 104 and 103 Ma, respectively. A Precambrian gneiss sample from the core of the Green Mountains near Londonderry, VT yielded an older AFT age of 123 Ma suggesting the possibility of increasing AFT ages to the east away from the Lake Champlain basin. Additional samples in process will better delineate this trend of young (~100 Ma) AFT ages in the southeastern Adirondacks and adjacent western Vermont.