Potential-field Investigations of the Williston Basin Basement

Transcription

1 Potential-field Investigations of the Williston Basin Basement Jiakang Li 1, Igor Morozov 1, and Glenn Chubak 1 Li, J., Morozov, I.B., and Chubak, G. (2005): Potential-field investigations of the Williston Basin basement; in Summary of Investigations 2005, Volume 1, Saskatchewan Geological Survey, Sask. Industry Resources, Misc. Rep , CD-ROM, Paper A-5, 11p. Abstract Simultaneous interpretation of gravity and aeromagnetic data from the Canadian part of the Williston Basin, taking into account other available information (geology, borehole, and seismic), was carried out as part of the Williston Basin Architecture and Hydrocarbon Potential Project. This study focuses on seamless and uniform processing and interpretation of the potential-field data in eastern Saskatchewan and western Manitoba, with an emphasis on highresolution imaging of the Precambrian basement. Processing methods include gridding, reduction to pole, downward continuation, horizontal and vertical derivatives, analytic signal, local wavenumber, and Euler deconvolution. The interpretation based on these new attribute maps provides a characterization of structural domains and potential basement faulting. Major structural contrasts and domains are identified within the Precambrian basement of the Williston Basin. The domains are determined primarily by magnetic characteristics of crystalline basement blocks combined with their gravity attributes. The boundaries between Precambrian blocks are commonly associated with high-gradient zones between the major high- and low-field anomalies. Within these domain blocks, major cross-cutting fractures can also be mapped from the trend patterns of gradient maps. Three major domains are recognized within the Williston Basin basement and analyzed for their internal structures: 1) the Sask Craton and Reindeer Zone, with its major north-south structural trend, 2) the Churchill-Superior Boundary Zone (CSBZ), and 3) the Superior Province, which is characterized by a number of east-trending subparallel domains. On top of these major structures, an additional group of linear features with weaker fabric is identified in the newly processed data maps. These northwest-trending features cross nearly the entire study area and are sub-parallel to the margin of the basin, suggesting that the deposition of Phanerozoic sediments could be genetically related to them. Keywords: gravity, magnetic, derivative, trend, boundary, fault, domain, basement, Williston Basin. 1. Introduction This study is part of the Williston Basin Architecture and Hydrocarbon Potential Project (Phase 1) undertaken in partnership with Industry, Economic Development and Mines (IEDM) of Manitoba, and Natural Resources Canada (NRCan) as a component of NRCan s second round of Targeted Geoscience Initiatives (TGIs). The project area extends from W96º to W106º, N49º to N56º, and covers much of eastern Saskatchewan and western Manitoba. The overall objective of the project is to produce a geological model of Phanerozoic strata of the Williston Basin over a significant portion of Saskatchewan and Manitoba to enhance our understanding of the hydrocarbon and mineral potential of these strata. This goal is being approached through subsurface geophysical, geological and hydrogeological mapping, and remotely sensed imagery analysis. More details on the project are available at The specific objective of the project s geophysical study presented here is to incorporate seismic, aeromagnetic, gravity, and remotely sensed imagery into a seamless (in particular, across the SK-MB border) 3-D regional geological model of the subsurface to improve our understanding of the Precambrian basement and its possible tectonic relationship with the overlying Phanerozoic rocks. For the purposes of this study, the Williston Basin was defined as the entire area south of the Precambrian Canadian Shield edge in Saskatchewan and Manitoba. With the available new data compilations, it becomes possible to achieve a seamless and consistent coverage across this entire area, link the existing isolated interpretations, provide basin-scale perspectives on geological structure and evolution, and extend geological mapping from the exposed regions into sediment-covered areas. A fundamental building block in these interpretations is the geophysical domain, distinguished on the basis of its potential-field anomaly trend, texture, and amplitude. Where the basement 1 Department of Geological Sciences, University of Saskatchewan, 114 Science Place, Saskatoon, SK S7N 5E2. Saskatchewan Geological Survey 1 Summary of Investigations 2005, Volume 1

2 is exposed, these domains often coincide with lithotectonic domains, which in turn depend on the scale of investigation. Structural trends identified from the geophysical anomalies may indicate the types of crustal and basin deformations in the area. In order to obtain an integrated characterization of the area, it is important to utilize a combination of geophysical attributes. Gravity and magnetic signatures most closely reflect the tectonic and structural characters of the area, and potential-field data also provide the necessary spatial continuity of coverage. However, due to its inherent limitations, potential-field mapping needs to be further calibrated and constrained by the available well logs and seismic data. Gravity data have been used successfully to map crustal-scale and basin-scale structural domains. Due to steeper distance dependence and higher susceptibility to the metamorphic and deformational processes within the crystalline rock, magnetic anomaly patterns are likely to be the primary indicators of the character of the basement in the covered regions. 2. Data The datasets consist of 235,413 gravity and 15,737,915 aeromagnetic survey points. Gravity data were collected from the 1950s to 1990s at various survey scales. In Saskatchewan and Manitoba, data sampling is highly variable, ranging in density from <1 km in the areas of oil and mineral exploration to 10 km or even more than 20 km in the east and northeast parts of the basin. For improved resolution, magnetic datasets interpolated to 200 m spacing were used in this work. 3. Data Processing and Inversion Methods To improve the resolution of gravity and magnetic images, and also to emphasize the effects of the geological contacts critical for the structural framework of the area, our data processing generally focused on accurate enhancement of the short-wavelength and linear features in the data. Processing began with interpolation and downward continuation of the point-gravity data using the Continuous Equivalent Source technique and derivation of the horizontal- and vertical-field gradients. Based on the results of these primary operations, several advanced attributes were also extracted. The key processing steps thus included: 1) Interpolation and gridding of the gravity data locally, the interpolation is performed into a rectangular grid, with the final results merged and stored in the form of a global latitude-longitude grid (see the following section). Where necessary, the interpolation can also include downward continuation in order to bring the data to a common datum. 2) Reduction to the pole (RTP) of the aeromagnetic data the reduction to pole can reduce the effect of Earth magnetic field and provide a more accurate determination of the position of source bodies. 3) First and second derivatives the maxima of the first horizontal derivative, and first and second vertical derivatives are commonly used to delineate the boundaries of source bodies and local anomalies. 4) 3-D analytic signal the analytic signal could be useful to reveal the basement structure. The maxima of analytic signal are located close to the outlines of the source (i.e., gravity or magnetic) bodies. The analytic signal (AS) is defined from the field derivatives as follows (Roest et al., 1992): 2 P P P AS = + + x y z 5) Local wavenumber attributes called TDR and THDR these operations suppress the longer wavelength anomalies and emphasize the effects of the sedimentary cover and of the basement. Local wavenumber attributes are defined from the vertical derivative (VDR) and the total horizontal derivative of the gridded field (THDR) as (Fairhead et al., 2004; Verduzco et al., 2004): 2 2 Tilt derivative: VDR TDR = tan 1 ( ); THDR Total horizontal derivative of TDR: TDR _ THDR = TDR x 2 2 TDR +. y Saskatchewan Geological Survey 2 Summary of Investigations 2005, Volume 1

3 6) 3-D Euler deconvolution this attribute provides estimation of source location and depth, including the faults and other sharp structural contrasts affecting magnetic strata. 3-D Euler deconvolution is performed through solving the equation (Thompson, 1982; Reid et al., 1990, Silva and Barbosa, 2003): ( x x0 ) T ( x, y, z ) + ( y y0 ) T ( x, y, z ) + ( z z0 ) T ( x, y, z ) = N T ( x, y, z ). x y z Here, T is the magnetic or gravity field and N is the structural index corresponding to the structural type (e.g., distinguishing point or linear sources) of interest. For gridded-data displays, it is important to utilize colour schemes that allow the best visual contrast and depth while offering a natural perception of the polarity and amplitude of the anomalies. The traditional rainbow palettes (used in Figure 1) may not always be the optimal choice. We experimented with a number of colour palettes Amgal Figure 1 - Interpolated Bouguer gravity anomaly map of study area. The white line indicates the edge of the Canadian Shield; dashed black line represents the Saskatchewan-Manitoba border. Saskatchewan Geological Survey 3 Summary of Investigations 2005, Volume 1

4 and preferred using bi-colour (blue-to-orange) palettes to display magnetic data. To improve the depth of colour rendering, we applied histogram balancing to the palettes. Such histogram-balanced palettes are derived from the actual data being displayed, and are designed so that each colour occupies approximately the same area of the resulting image. This is achieved at the expense of making the colour axis non-linearly dependent on the anomaly magnitudes, which is insignificant for visual perception. An example of such a histogram-balanced magnetic image is shown in Figure 2. HRSBZ HRSBZ SASK CRATON HUMBOLDT HUMBOLDT GLENNIE WAPAWEKKA TOBIN SMEATON SRBZ? RZ KISSEYNEW FLIN FLON CSBZ CSBZ BERENS RIVER SUPERIOR UCHI MOLSON PROVINCE EN G LISH RIVE PIKWITONEI PIKWITONEI R GODS LAKE ISLAND LAKE nt HRSBZ HRSBZ WYOMING WYOMING CRATON CRATON? BIRD RIVER? WINNIPEG RIVER WABIGOON Figure 2 - Map of aeromagnetic anomaly reduced to pole and interpolated. For display clarity, a histogram-balanced blue-toorange colour palette is used. With histogram balancing, every colour level occupies approximately the same area of the image. The white line indicates the edge of the Canadian Shield; green lines represent boundary-zone margins; black solid lines represent inter-domain boundaries; and dashed grey lines represent intra-domain boundaries between possible subdomain blocks. Green labels indicate major tectonic regions: CSBZ, Churchill-Superior Boundary Zone; HRSBZ, Hearne- Reindeer-Sask Boundary Zone; RZ, Reindeer Zone; and SRBZ, Sask-Reindeer Boundary Zone. Structural domains are labelled in black. Saskatchewan Geological Survey 4 Summary of Investigations 2005, Volume 1

5 4. Parallel Processing Analysis of large geophysical datasets, such as the gravity and aeromagnetic datasets of this project, poses stringent requirements to the organization and their efficient handling of the potential-field data. The sheer volumes of the datasets and their complexity (grids of variable densities, point and flight-line readings; seismic lines and well logs) first require careful pre-processing (data management, interpolation, and filtering) that cannot be carried out in a single process. The area thus has to be subdivided into smaller blocks that can be processed either sequentially or in parallel, using a multi-processor computer. Sequential data processing is most common, and was used in the processing examples presented below. However, in fulfillment of the project objective of making a seamless and accurate interpretation of very large datasets spanning a broad geographical area, we are also developing a framework for uniform, accurate, fast large-scale processing of potential-field datasets. This objective is achieved by utilizing Beowulf clusters as data-analysis workstations. Apart from the volume of the data, the need for subdividing the project s potential-field datasets into smaller blocks is dictated by the area of data coverage spanning two UTM zones. Potential-field analysis and inversion is normally done on a Cartesian grid, and only smaller blocks can be mapped onto such a grid with negligible distortions (Figure 3). The extracted rectangular data blocks then undergo a series of transformations (see above), after which they can be transformed into the latitude-longitude coordinate system and merged to form a continuous and distortion-free attribute grid. The novelty of our approach to potential-field data processing is in utilizing the data-management techniques that are normally used in seismic processing. The data blocks (Figure 3) are treated as multilayered 2-D seismic traces that are passed from one tool to another in the processing sequence, in a way that is routinely done in seismic processing. This allows combining multiple tools into complex and well documented processing sequences W106º W96º N56º N56º Single Data Block Y Y X X N49º N49º W106º W96º Figure 3 - Schematic subdivision of the study area into potential-field processing blocks (blue lines). Red dots are gravity stations and black contours represent the results of gravity interpolation. Details of data distribution are not essential here; however, note the large size of the study area and non-uniform data coverage, with most observations in the areas of oil exploration. Processing, such as interpolation from irregularly spaced survey points into a grid, is performed in local Cartesian coordinates (panel on the right, corresponding to the shaded blue block on the left from and into which the data are transformed using local stereographic projections. The resulting (e.g., filtered) grids are finally transformed back into latitudes and longitudes, and merged into the original global grid. Overlapping margins of the processing blocks are averaged in order to reduce the edge effects. Processing can be conducted concurrently using a parallel computer system. Saskatchewan Geological Survey 5 Summary of Investigations 2005, Volume 1

6 that could be executed concurrently. This use of modular seismic processing enriches potential-field data analysis with numerous additional tools (such as filtering, plotting, and potentially visualization) and provides a natural way for integration of potential-field and seismic data. Implementation of such a serialized and parallelized potential-field analysis is only possible with the use of a seismic-processing package that is capable of handling data types that are significantly more general than the traditional seismic records. Such a package was recently developed by Morozov (Morozov and Smithson, 1997). Recently, we built into this package an integrated Graphical User Interface and implemented extensive parallel processing functionality using the Parallel Virtual Machine. With potential-field processing and inversion tools integrated into the system, we expect to obtain a gravity- and aeromagnetic-data processing package of unusual pass-through, modularity, flexibility, and scalability. 5. Preliminary Results: Delineation of Boundaries and Structural Domains Identification of crustal blocks and domain boundaries is the key application of potential fields to geological interpretation. Previous gravity and magnetic mapping and domain analysis of Saskatchewan and Manitoba were carried out by Miles et al. (1997), Kreis et al. (2000), and Pilkington and Thomas (2001) respectively. In the present study, we focus on an integrated interpretation of the Williston Basin. Major basement domains should have pronounced expressions in aeromagnetic and gravity data. Domain boundaries cannot, however, be distinguished from other linear structural contrasts (e.g., created by stacking accreted terranes) on the basis of potential-field interpretation alone. Thus, we prefer a conservative term structural contrasts for the extended linear features observed in the maps, although many of these features could still be associated with significant basement blocks. Only seismic profiling across such features could provide definitive constraints of the degree of basement displacement associated with these contrasts. In our interpretation, major basement blocks and structural contrasts are identified mainly from the horizontal and vertical gradients and attribute maps. Domain boundaries are then roughly delineated by the areas of parallel or subparallel trends that have comparable amplitudes of the anomalies. This method was applied to both gravity and magnetic data. From a combination of gravity and magnetic results, we present the interpreted structural boundary and domain definition based on the additional and improved potential-field attributes as well as on seismic and welllog data and geological information. The various magnetic and gravity attributes describe the features and patterns of the basement blocks relative to their surrounding medium. For virtually any attribute, we look for spatial trends corresponding to the geologically known or inferred structures. The Bouguer gravity attribute map (Figure 1) outlines the lighter and heavier masses within the crust. Because the structural features within the crystalline basement have significantly stronger magnetic than density expressions, and also because magnetic-data spaces are much closer, the resulting magnetic attribute maps (Figures 2 and 4) are considerably more detailed than the Bouguer gravity map. The Williston Basin can be subdivided into three main regions with distinct structural patterns: 1) the central region, represented by the north-northeast trending Churchill-Superior Boundary Zone; 2) the western region, including Sask Craton and Reindeer Zone, with numerous northwest-, northeast- and near north-trending structural boundaries; and 3) the eastern region (Superior Province), which is mainly composed of a north-south stack of nearly east-trending boundaries and domains. These regions are outlined on Figures 2, 4, and 5. a) Churchill-Superior Boundary Zone The Churchill-Superior Boundary Zone (CSBZ), which crosses the entire Williston Basin within the study area and is marked by north-northeast trending linear anomalies with strong gravity highs (Figure 1); this trend changes to a north-south orientation near the Canada US border. The north-northeast trending magnetic fabric of the CSBZ contrasts strongly with the near east-trending magnetic anomaly patterns of the Superior Province and with the more complex magnetic patterns of the Reindeer Zone (Figure 2). Bleeker (1990) suggested that this change from magnetic low to high was related to Hudsonian metamorphic overprinting of granulites in the CSBZ, which destroyed magnetite through biotite-, hornblende-, and/or garnet-forming reactions. The low magnetic field over the northern margin of the CSBZ contrasts strongly with the eastern part of the Superior Province showing several large, strongly positive magnetic basement blocks (Figure 2). At the same time, the magnetic field character also changes significantly from north to south within the CSBZ. The western and eastern boundaries of the CSBZ are clearly defined by their gravity magnetic characteristics (Figures 2, 4, and 5). The western boundary corresponds to the boundary of north-northeast trending linear Saskatchewan Geological Survey 6 Summary of Investigations 2005, Volume 1

7 structure of the Flin Flon Domain in its northern part and extends southward to the edge of the study area. Its eastern boundary against the Superior Province is defined by a high magnetic gradient (Figure 4). b) Sask Craton and Reindeer Zone In the western region, we recognize eight sub-zones: the Reindeer Zone, the Sask-Reindeer Boundary Zone, the Wapawekka Domain, the Tobin Domain, the Smeaton Domain, the Humboldt Domain, the Hearne-Reindeer-Sask Boundary Zone, and the Wyoming Craton. The major structural boundaries and domains are shown in Figures 2 and 4. Note that from its magnetic signature, the unnamed area located south-southeast of the Humboldt Domain and extending from Regina south-southeast to Weyburn could be a part of the Hearne-Reindeer-Sask Boundary Zone nt/m Figure 4 - Vertical gradient of magnetic field reduced to the pole. Tectonic zones, domain boundaries, and the exposed Precambrian Shield boundary are indicated as in Figure 2. The white line indicates the edge of the Canadian Shield; green lines represent boundary-zone margins; and black solid lines represent inter-domain boundaries. Saskatchewan Geological Survey 7 Summary of Investigations 2005, Volume 1

8 mgal/km Figure 5 - Vertical gradient of gravity. This attribute is complementary to the reduced-to-the-pole magnetic field and can be used for additional constraining the domain and zone boundaries. Note how the contrasts between the Churchill-Superior Boundary Zone and Reindeer Zone, and also between the domains in the southwest part of the study area stand out better in this display. Lines defined as on Figure 4. (Figure 2). However, vertical gradient of the gravity field indicates that this block is clearly different from the adjacent boundary zones. From the magnetic and gravity anomaly and their vertical derivative maps, the amplitudes are clearly reduced in the Weyburn area, in which the Phanerozoic sedimentary thickness determined from well and seismic data gradually increases to 2600 m. The vertical gradients of potential field gradually decrease with increasing depth of the Precambrian sources, which facilitates understanding of the depth to the basement in any area. Along the western margin of the CSBZ, the Reindeer Zone manifests as a broad belt of low to moderate magnetic field containing small isolated magnetic highs and short quasi-linear magnetic highs. The Sask-Reindeer Boundary Zone, which cuts the Saskatchewan portion of the Williston Basin into two parts, is well expressed in negative narrow linear north-south trends on magnetic and gravity gradient maps (Figures 2 and Saskatchewan Geological Survey 8 Summary of Investigations 2005, Volume 1

9 5). On both sides, it has clear boundaries defined from the amplitudes and gradients of magnetic anomalies. This zone extends from the Precambrian margin in the north, continues straight south to approximately N50º30, and then turns south-southeast, adjacent to the Wyoming Craton. The zone exhibits no clear gravity boundary (Figure 1), although some gravity anomalies are located within it. The Tobin Domain is widest in the north and narrows towards the south, where overlapping magnetic and gravity highs are observed (Figure 2). South of about N53º30, it becomes a narrow tract with strong magnetic contrast with the adjacent areas. The domain is characterized by strong positive magnetic anomalies and moderate-intensity gravity anomalies. The Smeaton Domain between the Tobin Domain and the Humboldt Domain is a low negative magnetic anomaly area that corresponds to a gravity high. It appears as an independent weakly magnetic block placed between two high-intensity magnetic blocks. The Humboldt Domain shows similar characteristics to those of the Tobin Domain: high-intensity magnetic anomaly with some interior boundaries subdividing it into sub-domain blocks. In its northern part, the trend of its magnetic fabric is north-northeast, but towards the south, its magnetic trend is oriented north-northwest. Thus, this domain may potentially be considered as consisting of two distinct sub-domain blocks. The Hearne-Reindeer-Sask Boundary Zone is a northwest-trending, narrow belt with a negative magnetic anomaly located between the Sask Craton and the Wyoming Craton. Finally, in the southwestern corner of the study area, part of the Wyoming Craton is represented by a zone of gravity low (Figure 1) and magnetic high (Figure 2). The Wyoming Craton is characterized by its strongly magnetic crystalline basement and topographic high (not shown here). c) Superior Province From their magnetic-field character, the Superior Province domains mapped within the Precambrian Shield are seen to extend into the eastern part of the Williston Basin. The Superior Province within the study area has been subdivided into east-trending parallel domains (Card and Poulsen, 1998; Pilkington and Thomas, 2001). From north to south, these domains are: Gods Lake, Molson, Island Lake, Berens River, Uchi, English River, Bird River, Winnipeg River, and Wabigoon (Figure 2). Each of these domains has a clear margin separating it from other domains (the separation between the Bird River and Winnipeg River domains is, however, less distinct). Most of these domain boundaries are gradient zones with negative magnetic anomalies (Figures 2 and 4). The intensities and trends of magnetic anomalies within the domains can commonly be used for defining the interior sub-domain blocks. The common characteristics of the Superior Province domains within the study area are their high-intensity magnetic fields and clear boundaries with the CSBZ, where gravity-anomaly trends essentially coincide with the magnetic trends. The Berens River Domain can also be subdivided into two sub-domain blocks based mainly on the presence of distinctive linear magnetic features that may signify major faults rather than boundaries between compositionally different blocks (grey dashed line in Figure 2; Bleeker, 1990; Pilkington and Thomas, 2001). The southwestern sub-domain block of the Berens River Domain is cross-cut by a northwest-trending feature that appears to also overprint the Churchill-Superior Boundary and Reindeer Zones (Figure 6). This and other similar features are discussed below. d) Northwest-trending Magnetic Contrasts Along with the main structural-domain subdivisions discussed above, additional weaker linear magnetic contrasts were also found (Figure 6). These features have short spatial wavelengths and consequently they could be related to the upper part of the basement or associated with magnetized sediments. The northwest-trending magnetic contrasts extend from the Sask Craton to the Superior Province, crossing nearly the entire study area and overprinting the basement blocks with different potential-field signatures. They are located close to the Precambrian margin of the basin, and deposition of Phanerozoic sediments may thus be genetically related to them. Similar structures may also exist in the deeper parts of the basin, as indicated by identification of major basement faults in several seismic studies (Hajnal et al., 1996; Hamid et al., this volume). However, observation of these structures at depth using magnetic data is difficult because of the loss of high-frequency resolution with depth. 6. Conclusions Using conventional and recently developed 3-D potential-field data processing methods, structural domains and boundaries within the Williston Basin TGI study area are identified. Combinations of the horizontal and total Saskatchewan Geological Survey 9 Summary of Investigations 2005, Volume 1

10 nt?? Figure 6 - Weak, linear, narrow northwest-trending basement contrasts (dashed black lines) presented on magnetic background. Note that these features overprint the boundaries of tectonic zones and domains (Figure 2). gradient, analytic signal, Euler deconvolution, and local wavenumber attributes maps offer the best horizontal resolution, and also provide ways for estimating the depths to the magnetic sources. The Williston Basin in Canada is subdivided into three structural regions: the Churchill-Superior Boundary Zone characterized by gravity highs, clear boundaries, and north-northeast trending structural trends; the Sask Craton and Reindeer Zone with numerous near-north-south magnetic trends; and the Superior Province, a north-south stack of structural domains with predominantly west-east trends. On top of these regional domain patterns, weaker, linear magnetic contrasts are found close to the margin of the Precambrian Shield. These features cut across the domain and structural boundaries and may possibly be related to faulting genetically associated with sediment deposition in the basin. Similar features might also exist within the deeper parts of the basin where their detection using surface data is difficult because of the loss of resolution with depth. Saskatchewan Geological Survey 10 Summary of Investigations 2005, Volume 1

11 7. Acknowledgments Many researchers from: Saskatchewan Industry and Resources; Manitoba Industry, Economic Development and Mines; the Potash Corporation of Saskatchewan; and the Geological Survey of Canada contributed to this project. Special thanks go to W. Miles (Geological Survey of Canada) who provided the potential field datasets, A. Costa (Petroleum Geology Branch, Saskatchewan Industry and Resources) for providing the well data, and S. Sule (University of Saskatchewan) for his preliminary seismic interpretations. Olympic Seismic donated seismic data used to calibrate the potential-field results. Critical reviews by Z. Hajnal and B. Pandit (University of Saskatchewan), and F. Haidl and C. Gilboy (Saskatchewan Industry and Resources) have greatly helped in improving this manuscript. GMT programs (Wessel and Smith, 1995) were used in preparation of the illustrations. 8. References Bleeker, W. (1990): New structural-metamorphic constraints on Early Proterozoic oblique collision along the Thompson Nickel Belt, Manitoba, Canada; in Lewry, J.F. and Stauffer, M.R. (eds.), The Early Proterozoic Trans-Hudson Orogen of North America, Geol. Assoc. Can., Spec. Pap. 37, p Card, K.D. and Poulsen, K.H. (1998): Geology and mineral deposits of the Superior Province of the Canadian Shield; in Lucas, S.B., St. Onge, M.R., and Percival, J.A. (comps.), Geology of the Precambrian Superior and Grenville provinces and Precambrian fossils in North America, Geology of Canada Series, No. 7, Geol. Surv. Can., p Fairhead, J.D., William, S.E., and Flanagan, G. (2004): Testing magnetic local wavenumber depth estimation methods using a complex 3-D model; Soc. Expl. Geophys., 2004 Annual Meeting, Denver, exp. abstr., p Hajnal, Z., Lucas, S., White, D., Lewry, J., Bezdan, S., Stauffer, M.R., and Thomas, M.D. (1996): Seismic reflection images of high-angle faults and linked detachments in the Trans-Hudson Orogen; Tectonics, v15, p Kreis, L.K., Ashton, K.E., and Maxeiner, R.O. (2000): Interpretive geophysical maps of Saskatchewan, Sask. Energy Mines, Open File Rep , Sheet 1 of 8. Miles, W., Stone, P.E., and Thomas, M.D. (1997): Magnetic and gravity maps with interpreted Precambrian basement, Saskatchewan; Geol. Surv. Can., Open File 3488, maps at 1: scale. Morozov, I.B. and Smithson, S.B. (1997): A new system for multicomponent seismic processing; Comp. Geosci., v23, p Reid, A.B., Allsop, J.M., Granser, H., Millete, A.J., and Somerton I.W. (1990): Magnetic interpretation in three dimensions using Euler deconvolution; Geophys., v55, p Roest, W.R., Verhoef, J., and Pilkington, M. (1992): Magnetic interpretation using the 3-D analytic signal; Geophys., v57, p Pilkington, M. and Thomas, M.D. (2001): Magnetic and gravity maps with interpreted Precambrian Basement, Manitoba; Geol. Surv. Can., Open File 3739, maps at 1: scale. Silva, J.B. and Barbosa, V.C. (2003): 3-D Euler deconvolution: Theoretical basis for automatically selecting good solutions; Geophys., v68, p Thompson, D.T. (1982): EULDPH: A new technique for making computer-assisted depth estimates from magnetic data, Geophys., v47, p Verduzco, B., Fairhead, J.D., and MacKenzie, C. (2004): New insights into magnetic derivatives for structural mapping; The Leading Edge, v24, p Wessel, P. and Smith, W.H.F. (1995): New version of the Generic Mapping Tools released; EOS Trans. Amer. Geophys. Union, v76, p329. Saskatchewan Geological Survey 11 Summary of Investigations 2005, Volume 1