MESOZOIC THERMAL EVOLUTION OF THE HIGH PEAKS REGION OF THE ADIRONDACK MOUNTAINS, NY: CONSTRAINTS FROM APATITE FISSION TRACK THERMOCHRONOLOGY

The Adirondack Mountains, with local relief approaching 1 km, are comprised of dominantly high-grade metamorphic rocks that record a protracted geologic history spanning the Grenville orogeny, Late Precambrian continental breakup, the Taconic orogeny, and Carboniferous burial. To constrain the post-Triassic low temperature thermal evolution of the high peaks region of the Adirondack Mountains a vertical sampling profile (~900 m of relief) was collected on Mount Marcy for apatite fission track (AFT) and (U-Th)/He thermochronologic analysis.

Results from an AFT age vs. elevation plot containing 9 samples yields variable cooling rates during the Late Jurassic through the Early Cretaceous. A cooling event of limited magnitude is revealed by a steeper age vs. elevation slope. The late Jurassic age of this event is considered a minimum age since annealing continued during and subsequent to this cooling event, as indicated by mean track lengths of 13.3-12.5 µm with standard deviations >1.7 µm. These results suggest that in the high peaks region cooling rates were more variable than previously suspected during the Late Jurassic-Early Cretaceous.

Numerous modeling runs using the multi-kinetic AFT computer-modeling program AFTSolve (Ketcham et al., 2000), that derives best-fit cooling histories from AFT age and track length information, did not produce a variation in Late Jurassic-Early Cretaceous cooling rates, nor a cooling event such as observed in the age vs. elevation plot. The absence of this variability and cooling event in thermal models may be due to the limited magnitude of the cooling event and the dilution of the Late Jurassic-Early Cretaceous thermal signal by the accumulation of post-Early Cretaceous tracks.

There are a number of possible mechanisms for a late Jurassic cooling event. The crossing of North America over a hotspot, e.g. the Great Meteor Hotspot, could have caused an increase in the geothermal gradient and subsequent relaxation of isotherms and/or denudation from thermal doming. Alternatively, regional faulting caused by far-field stress related to rifting and the propagation of sea-floor spreading in the North Atlantic could have also resulted in denudation associated with the creation of relief.