Possible evidence for contemporary doming of the Adirondack Mountains, New York, and suggested implications for regional tectonics and seismicity

Abstract

The Adirondack Mountain massif is a dissected elongate dome having a north-northeast axis about 190 km long, and an east—west dimension of about 140 km. The dome exposes a core of Proterozoic metamorphic rocks from which the Paleozoic cover rocks have been eroded, except in several north-northeast-trending graben. The minimum amplitude of the dome, based on a ‘reconstruction’ of the Proterozoic—Paleozoic unconformity is 1600 m. The Adirondack dome is an anomalous feature of the eastern edge of the North American craton. It differs from other uplifts in the Interior Lowlands of the craton not only in terms of the greater combined amplitude and area of its uplift, but in the present high elevation of its Mountains (up to 1600 m) which are unequalled on the craton except along the Rocky Mountain front and in the Torngat Mountains of northernmost Labrador. This prompted an interest in the possibility that the Adirondack dome has undergone neotectonic regeneration and may be undergoing domical uplift at the present time. Accordingly, leveling records were consulted at the National Geodetic Survey data base in Rockville, Maryland, and used to construct leveling profiles. The most informative of these extends north—south along the block-faulted eastern flank of the Adirondack dome, extending from Saratoga Springs to Rouses Point, a distance of 245 km. A comparison of the level lines for 1955 and 1973 demonstrates that arching has occurred. An uplift of 40 mm along the central portion of the line, and a corresponding subsidence of 50 mm at the northern end, has produced a net increase in the amplitude of arching of 90 mm in the 18-year interval. This differential uplift, particularly with subsidence at the northern end, argues for a tectonic rather than glacio-isostatic mechanism. Pending releveling across the center of the Adirondack dome, it is tempting to extrapolate the releveling profile and suggest that the Adirondacks as a whole may be undergoing contemporary doming at a rate far in excess of denudation. This inference leads to a consideration of other tectonic features which may be related in both the short and long term to such a postulated doming. One is the periodic occurrence of anomalous earthquake swarms located very near the geometric center of the Adirondack dome at Blue Mountain Lake, although horizontal rather than vertical compressive stresses have been shown to be dominant by Sbar and Sykes in 1973. Another, is the predominance of faults and topographic lineaments in the Adirondacks which parallel the long axis of the dome and are so remarkably well displayed in the infrared bands of ERTS-1 imagery.