The Adirondack Mountains in upstate New York represent a distinctive exposure of Precambrian Grenville age, ~1.1 byr, metamorphic and metaigneous rocks. Apatite fission-track (FT) ages determined for three samples of Precambrian metamorphic rocks from the High Peaks and Saranac Lake regions range from 135 ± 26 to 166 ± 30 Ma. These apatite FT ages indicate unroofing of the Adirondack massif during the Early Cretaceous.

Thirteen previously determined apatite FT ages from the Adirondack region are consistent with the above ages. This collective data indicates an unroofing history beginning in the Early Cretaceous for the western and central Adirondacks. Samples from the southeastern Adirondacks yield significantly younger apatite FT ages, 104 ± 9 to 83 ± 11 Ma, indicating later denudation.

Two anorthosite samples from the Dix Mt. range taken at a maximum elevation difference are being analyzed for apatite FT ages and track lengths. This data will provide an estimate of the rate of unroofing in the High Peaks.

Apatite FT length distributions yield mean track lengths ranging from 13.0 ± 1.5 mm to 13.7 ± 1.4 mm. Samples from the Lyon Mt. area to the north yield thermal histories, based on track length measurements, which suggest a reheating episode at ~100 Ma. Additional track length measurements will be determined for other northern samples to support modelled thermal histories.