INTERPRETATION OF GRAVITY ANOMALIES IN THE TUG HILL PLATEAU

Recent studies by J.L. Wallach and M. Rheault of the Tug Hill Plateau between Lake Ontario and the Adirondack Highlands suggest the plateau is an uplifted and internally faulted fault-bounded block. They state the Carthage-Colton shear zone is a steeply inclined, reactivated fault zone that allowed the Tug Hill to rise in response to uplift in the Adirondack Highlands.

Thirteen hundred and thirty five gravity measurements were made in the Tug Hill Plateau and along that Carthage-Colton shear zone. A gravity gradient occurs along the CCSZ, separating the higher density rocks of the Adirondacks Lowlands from the low-density rocks of the Adirondack Highlands and Tug Hill Plateau. This gradient extends along the northern and western boundary of the Tug Hill Plateau.

The Tug Hill plateau has a gravity low surrounded by higher gravity values. The lower gravity values could be due to lower density rocks in the basement and their uplift in the plateau. In the Adirondack Highlands a similar gravity low occurs over an anorthosite slab with two roots. The low over the Tug Hill plateau may have a similar origin. Three gravity lows within the plateau may be due to the roots of the anorthosite.