Fracture Patterns on the Canadian Shield: A Lineament Study with Landsat and Orbital Radar Imagery

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Sixty Landsat scenes of the Canadian Shield have been used to map lineaments in a test of the regmatic shear theory, and to evaluate orbital remote sensing methods for the study of high-latitude low-relief shields. It has been found that most lineaments represent a natural class of brittle fractures (joint sets or normal faults) formed by crustal extension. Many lineaments are associated with Precambrian diabase dyke swarms, suggesting that both they and parallel unfilled fractures resulted from uplift and bending of the crust by mantle plumes. There is no unified lineament pattern for the entire shield or even for crustal provinces. However, photogeologic interpretation may be biased against compressional features which may be mylonite zones not differentially eroded, and many thrusts, reverse faults, and wrench faults have probably been missed. Accordingly, the negative results of this study do not necessarily constitute decisive disproof of the regmatic shear theory. The most effective visual range imagery has been found to be near-infrared Multispectral Scanner scenes taken late in the fall. However, orbital radar imagery from Seasat and the Shuttle Imaging Radar system has been shown to be useful for structural mapping if taken with near-vertical incidence angles and illumination nearly normal to structural trends, when strong highlighting occurs. Further investigations of shield structure using higher resolution (20 meter) visual range sensors with stereoscopic coverage, and with orbital radar, are of great potential value.