Revisiting the Lineament Study of the Sudbury Impact Structure Using Recent Remote Imagery

Introduction: The Sudbury impact structure is one of three large complex impact basins on Earth that provide unique opportunities to understand the structural characteristics of multi-ring impact basins [1]. The impact event formed ~1.85 Ga, resulting in a ~200 km diameter impact structure [2]. The structural expression at Sudbury is very complex with evidence of extensive post-impact tectonism [3-5]. The elliptical shape of the basin is the result of tectonic shortening in the northwest-southeast direction, leading to the deformation and folding of the basin, the greatest deformation occurring along the South Range [6]. The deformation process has resulted in the preservation of several impactite units within the main basin area including a differentiated impact melt sheet (the Sudbury Igneous Complex or SIC), brecciated rocks, target rocks, and post impact geological processes [7, 8]. However, post impact erosion has removed much of the impactites beyond the SIC, with the exception of offset dykes and parautochtonous [9] rocks from the crater floor [10]. Offset dykes are igneous intrusions that extend metres to hundred metre-scale and occupy roughly radial and concentric structures around the basin. Previous studies have proposed the presence of several ring structures based on field observations and low resolution remote sensing datasets, including the transient cavity, crater edge, and structural uplift proposing a multiring structure similar to Vredefort [11, 12]. The apparent crater diameter range from 150 – 260 km [13, and references therein]. Assessing the structural characteristics of the Sudbury impact structure using current remote sensing datasets (within improved spatial and spectral resolutions than in previous studies) can help constrain the extent of these proposed ring structures. The improved data resolutions may also provide better tools to identify the extent of offset dykes beyond the main melt sheet (SIC), and the Sudbury breccia providing further context to field observations (e.g. 13, 14). Methods: This study extends earlier work done by [11] of performing basic lineament analysis on a variety of remote sensing datasets to assess the regional extent of lineaments (e.g. faults). While prior lineament studies for Sudbury have conducted the analyses manually digitizing their results at the end, this study approaches the method by using automated techniques to assess the lineament distribution. Studies using automated extraction techniques have reported a higher lineament number count compared to more traditional methods, minimizing power and saving time [15]. Due to the extensive deformation along the south range of the SIC, the study has focused on areas north northwest of the SIC, beyond the North Range. This study was done over a region extending ~150 km away from the centre of the Sudbury basin. Automated lineament analyses was done using techniques outlined by [15] on Landsat 7 (ETM+) and digital elevation models (DEMs). Compared to previous studies that used Landsat 4 (MSS), Landsat 7 data has higher spatial and spectral resolution that allowed for a more detailed analyses of the area with wavelength bands not previously available. Table 1 summarizes the resolution details between this study and previous studies. Shaded relief images were derived DEMs with different sun azimuth directions: 0, 45, 90, 135, 180, 225, 270, and 315. PCI Geomatica was used to derive automated lineament extraction (using the LINE algorithm), and strike measurement (using the DIP algorithm). Furthermore, the EDGE algorithm was applied to enhance lineaments, drainages, and landforms in each of the images. The extracted lineaments were statistically analyzed to determine lengths, densities to generate rose diagram and assess lineament density. The lineaments were compared to known geology, and sets of lineaments were recorded based on their strike direction and length. Rose diagrams were plotted using GeoOrient. using rose diagrams, and lineament density maps. Delineation of drainage system from DEM data was achieved using the ArcHydro tools within the ArcGIS suite.