LOW TEMPERATURE THERMOCHRONOLOGIC STUDIES IN THE ADIRONDACK HIGHLANDS

The Adirondack Highlands form a north/south trending oval exposure of Proterozoic (ca. 1.3-1.0 Ga) high-grade metamorphic rocks in a rugged terrain that locally rises over 4,000 ft and reaches approximately 1 km of relief. This study investigates the origin of the landscape in the High Peaks and Southeastern regions of the Adirondack Highlands. Through the application of (specific) sampling strategies using the apatite fission track and (U-Th)/He thermochronometers, we test whether the landscape in these regions formed during events which occurred during the Middle Jurassic to Tertiary and/or resulted from faulting after the region cooled below the apatite fission track closure temperature. In addition to thermochronologic analysis, a kinematic analysis of brittle faults exposed in both study regions is underway.

In the High Peaks region, a vertical profile has been collected down Mount Marcy covering approximately 900 m of relief with a sampling interval of 100 m. Amounts and rates of Middle Jurassic to Early Tertiary denudation will be constrained from this profile through analysis of age vs. elevation plots and computer modeling of apatite fission track and (U-Th)/He data. In the Southeastern Adirondacks a vertical profile has been collected down Prospect Mountain, which covers approximately 500 m of relief, from which denudation rates will be constrained in this region.

It has been suggested by others (Roden-Tice et al., 2000) that Late Mesozoic faulting has occurred across the numerous northeast/southwest striking faults found throughout the Southeastern region. In the present study, samples were collected across the northeast striking western boundary fault of the Lake George graben. Apatite fission track stratigraphy will be used to test whether any substantial movement has occurred across this feature subsequent to cooling below the apatite fission track closure temperature. The preliminary results of this study are presented, which imply changes in denudation rates during the Late Mesozoic.