Applications of water-based magnetic gradiometry to assess the geometry and displacement for concealed faults in the southern Adirondack Mountains, New York, U.S.A

An integrated magnetic gradiometry and structural analysis was conducted on three lakes in the southern Adirondacks Mountains, New York, in order to develop a geometric and kinematic model for concealed and long lived faults that transect the Proterozoic basement structures, offset Paleozoic strata to the south, and may be associated with the development of the post-Paleozoic cratonic dome (the Adirondack dome). Two lakes occur along the trace of two of the most prominent topographic lineaments that have been proposed to be faults in the southern Adirondack Mountains, and a third lake is located at the apparent fault intersection. Hinkley Lake occurs over the east–west trending lineament that corresponds to the trace of the Prospect fault. Indian Lake resides in a set of north–northeast trending pronounced lineaments that transect an anorthosite-cored structural dome and are inferred to be faults on the NYS geologic map. Piseco Lake is immediately adjacent to the intersection of the two proposed fault zones (Prospect and Indian Lake fault zones). Magnetic surveys were conducted on all three lakes, resulting in anomaly maps. Accompanying two dimensional geologic models for Hinkley and Piseco Lake were produced. At Piseco Lake, field evidence supports a brittle deformation history with sinistral-normal displacement. A similar deformation history is consistent with field data collected at Indian Lake. Correlation of the two dimensional magnetic models resulted in a sinistral, releasing-bend fault geometry beneath Piseco Lake, and the fault truncation of a granitic gneiss cored antiform for the subsurface geology of Hinkley Lake. The magnetic data and models suggest that Piseco Lake resides over a sinistral, pull-apart structure with sufficient throw to preserve the lowermost Paleozoic strata that once covered much of the Adirondack dome. This would account for both sinistral strike-slip and normal displacement on the interpreted faults, at Piseco and Indian Lakes, and rotation of structural blocks as the result of fault interaction. Relative timing, regional relationships, and ties to published ages suggest that the distribution of the faults is a relic of Neoproterozoic Iapetan rifting, Paleozoic displacement, and Mesozoic uplift of the Adirondack dome. Finally there is probable correlation of these faults with modern seismic activity.

► Magnetic gradiometry on Adirondack Lakes, New York to located concealed faults.
► Magnetic anomalies and models integrated with fracture and lineament data.
► Faults exhibit oblique sinistral displacement within a crust-scale domino structure.
► Proterozoic faults with protracted Ordovician, Cretaceous, and neotectonic activity.