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Mapping Precambrian basement structure beneath the Williston Basin in Canada; insights from horizontal-gradient vector processing of regional gravity and magnetic data

, : Mapping Precambrian basement structure beneath the Williston Basin in Canada; insights from horizontal-gradient vector processing of regional gravity and magnetic data. Canadian Journal of Exploration Geophysics 34(1-2): 40-48

Horizontal-gradient vector (HGV) processing of regional gravity and aeromagnetic data from southeastern Saskatchewan and southwestern Manitoba is undertaken as part of a study of Precambrian basement geology beneath the Williston Basin in Canada. The HGV method resolves potential-field anomalies in more detail than do many other data enhancement techniques. In HGV maps, the horizontal gradient of the gravity or magnetic field is treated as a vector, having both a direction and magnitude. The gradient is represented on a map as an arrow with an origin at a grid node. Varying the arrow polarity (uphill or downhill--towards or away from local maxima in the potential field) provides HGV displays with differing images of potential-field anomaly fabric. HGV patterns within the study area are highly variable and include linear and curvilinear anomalies of varying orientations, and circular and ovoid anomalies occurring singly and in curvilinear belts. These patterns indicate crystalline basement beneath this part of the Williston Basin is composed of a complex mosaic of crustal belts, faults, and plutons. The analysis of HGV-processed potential-field data provides new insights into the crustal structure and tectonic fabric of the Archean Superior Province, Proterozoic Trans-Hudson Orogen, and intervening Churchill-Superior boundary zone beneath the northern Williston basin. East-west and north-south aligned potential-field anomalies outline the main Kenoran (2.8-2.4 Ga) and Hudsonian (1.9-1.8 Ga) age crustal fabrics, respectively. In magnetic HGV maps, the transition from E-W-trending (Superior Province) to N-S-trending (Churchill Province) crustal fabrics commonly appears gradational or irregular, suggesting the Churchill-Superior "boundary zone" within the study area is broad and structurally segmented. In gravity HGV maps, a prominent N-S aligned belt of ovoid-shaped anomalies appears to provide a regionally consistent potential-field signature for part of the boundary zone. The Tabbernor fault zone in the central Trans-Hudson Orogen can be identified in magnetic HGV maps, but is not readily apparent in gravity maps. Interpretation of Precambrian basement domains and trends provides a regional framework for detailed investigations of basement sedimentary cover interaction in this economically important part of the Williston Basin.


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