FRACTURES IN THE MESOPROTEROZOIC ADIRONDACK BASEMENT AND THE LINK TO FRACTURES IN THE OVERLYING PALEOZOIC STRATA

NNE striking oblique-slip faults divide the basement of the Adirondacks into several structural blocks. Mesozoic differential uplift of these blocks contributed to the rise of the Adirondack dome. These faults extend southward into the Mohawk Valley fault system that was active during the development of the early Paleozoic shelf, and reactivated during various Appalachian tectonic events. An E-W transect to systematically study fracture systems in the Adirondacks was carried out across the massif. This work was done to compare with fracture systems in the overlying Paleozoic strata. There are two fracture sets that occur within the Indian - Piseco lakes fault block: NNE & NW striking. West of the Indian Lake fault, and within the region of the Prospect fault, there are two fracture sets: NNE & E-W striking. Farther west within the Hoffmeister fault block, the E-W striking fractures are dominant, the NNE striking fractures are present, and a third NE striking set is present. The westernmost region of the Adirondacks, within the Moose River valley, there are four fracture sets: E-W, NW, NNE and NE striking. The region between Piseco Lake and the Moose River is devoid of the NW striking fracture set that occurs everywhere else. Middle Ordovician Black River and Trenton Group carbonates overly the basement immediately to the west. There are four fracture sets within the carbonates that are subparallel to basement fractures. The overlying Utica shale contains NW, NNE and NE striking fractures with the NW set being most abundant west of the Adirondacks. All of the formations in the Lorraine Group have prominent NW and NE striking fractures. Along the transect, steeply dipping ENE & NNE striking meso-scale faults were observed in the basement. Meso-scale normal faults in the overlying carbonates are parallel to those in the basement, and this relationship continues into the Utica shale. No meso-scale faults were observed in the lower Lorraine Group, but the Oswego sandstone has sinistral meso-scale faults that strike ENE parallel to one of the two fracture sets. There appears to be a direct link between the fractures and meso-scale faults in the basement and in the overlying strata. It is interesting to note that two of the fracture sets (ENE and NW striking) that occur in the basement are ubiquitous throughout the northern Appalachian basin.