FRACTURE ANALYSIS ALONG THE KANAWAUKE FAULT ZONE, HUDSON HIGHLANDS, NEW YORK

The Kanawauke fault forms a pronounced topographic lineament that trends 072 in the Mesoproterozoic rocks of the western Hudson Highlands, NY. The Kanawauke fault merges with the Ramapo fault in the region of Tuxedo Park, and lies within a minor belt of earthquakes. Based on the geologic map, quartzofeldspatic and mafic gneisses show dextral offset across the fault. Much of the fault is concealed by water bodies and talus, and there are few field locations where the shear sense can be determined directly. An integrated study of the available LIDAR imagery and fracture systems in the field was undertaken to better constrain the strain history. Fractures were mapped in a 2 km wide corridor immediately north and south of the Kanawauke fault. This corridor contains abundant bedrock exposures thereby providing sufficient control to document any fracture intensification associated with fault proximity. At each outcrop, the orientation of fractures and spacing were documents per fracture set. A high resolution map of fracture orientations and spacing was constructed and superimposed on the DEM. The DEM was used to locate large fractures that would not be apparent while in the field, in addition to a fracture trace analysis. There are three steeply dipping fracture sets that strike N-S, NNE and NW. The N-S and NNE striking fractures persist through the study area, but are best developed in the regions near the fault. The third fracture set varies in strike from NW to nearly E-W, and correlate well with arcuate fracture traces observed in the DEM images. The field results are consistent with the DEM fracture trace analysis, and fracture spacing decreases within several hundred meters of the fault trace. One location within the fault zone contains cemented fault breccia, gouge, polished surfaces, and subhorizontal slicks. We interpret the three fracture sets to be R-, P- and R’-shear fractures, that are consistent with overall dextral shear on the fault.