MESOZOIC UNROOFING HISTORY OF EASTERN NEW YORK AND WESTERN NEW ENGLAND BASED ON APATITE FISSION-TRACK AGES

Early to Late Cretaceous apatite fission-track (AFT) ages (~80-115 Ma) dominate the down-faulted area and summits on both sides of Lake George and continue northward along the heavily normal-faulted western margin of the Lake Champlain - Adirondack Mountain region of New York state. Samples of Precambrian gneiss from the eastern shore summits of Pilot Knob (659 m) and Buck Mt. (711 m) on Lake George yielded AFT ages of 96 and 114 Ma, respectively. Previously determined AFT ages for samples taken along the western shore of Lake George range from 89 Ma for the Cambrian Potsdam sandstone at Hearthstone Point to 105 Ma for Precambrian gneiss near Bolton Landing. Samples of Precambrian gneiss from down-faulted western shore of Lake Champlain near Crown Point, the Cambrian Potsdam sandstone and Precambrian gneiss south of Ticonderoga yielded young AFT ages of 84, 89 and 89 Ma, respectively. The large areal extent of AFT ages in the range of 80 to 120 Ma throughout the southeastern Adirondack Mountains and east-central New York state indicates Early to Late Cretaceous unroofing was widespread. The consistency of AFT ages between summits and adjacent down-faulted blocks suggests that the unroofing was not fault-controlled.

An AFT age discontinuity exists between Precambrian samples from southern Vermont at Bennington (103 Ma) and northwestern Massachusetts at Dalton (170 Ma). There is also a trend of eastward increasing AFT age for samples of Cambrian Rensselaer Graywacke in eastern New York from 116 Ma at Cropseyville to 142 Ma near Nassau. Five additional AFT ages for samples southern Vermont and western Massachusetts will be determined in order to better delineate these age changes and relate them to Mesozoic unroofing history of New York and New England.