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This Open File contains the interpreted brittle lineaments and a compilation of mapped faults of an area bound by latitudes 44°N and 48°N and longitudes 73°W and 80°W. The area includes most of the Ottawa River watershed. It also covers most of eastern Ontario and the Laurentians, between Montréal (QC) and North Bay (ON). The study area includes the seismically active region known as the Western Quebec Seismic Zone (WQSZ). The WQSZ is an area where earthquakes as large as magnitude 6.2 have occurred in the past and where tens of smaller earthquakes are recorded yearly. Our study is an attempt to provide a homogeneous coverage of these brittle structures through an integration of visually interpreted lineaments and mapped faults. The possible relationships between these brittle faults and earthquakes will be examined later. Lineaments were observed mostly from the Digital Elevation Model (DEM) of the Canadian National Topographic Data Base (NTDB) at a scale of 1:250 000. The DEMs illuminated from two directions were used to first visually recognize lineaments and second, to georeference their surface expressions in a Geographic Information System (GIS). Since the final goal was to better map the brittle faults that could be reactivated in earthquakes, the clear ductile structures were not considered in this study and the more questionable ones re-evaluated subsequently against known geological information. Most of the region of interest is southeast of the Grenville Front, where all ductile structures are related to the Grenville orogeny (about 1 billion years ago). The recognition of brittle structures is based on the observation that they are essentially linear in plan view. On the other hand, the ductile structures are generally curved, enhance contact between different Grenvillian lithologies, or present a distinct structural pattern. With a few exceptions, only lineaments with a length greater than 5 km were included. After a first detection pass, lineaments at a more regional scale were drawn by interpolating between segments of lineaments. These interpolated segments corresponded to areas where the topography was subdued and where no conspicuous trace existed. The interpreted lineaments were then compared with the provincial geological maps of Quebec and Ontario, which often did not distinguish between brittle faults and ductile shear zones. Lineaments that coincided with diabase dykes were recognized by consulting geological maps and by examining the total magnetic field. Our final product is a 1:750,000 scale map that can be used in the future to better understand the seismotectonics of this region.

The nature and extent of potential source bodies associated with prominent, regional-scale gravity and magnetic anomalies in the northern Québec Appalachians are investigated through forward modeling. Potential field anomalies are interpreted to be the geophysical expression of basalt flows extruded during the Neoproterozoic to Cambrian rifting of Laurentia, prior to opening of Iapetus. Geophysical modeling provides substantial new constraints on seismic and structural crosssections and the map distribution of volcanism. This study indicates that the volcanism was significantly more widespread than previously recognized. Basaltic rocks form a sheet up to 4 kilometers thick, transported on the main Taconic décollement. Most of this sheet is deeply buried and overlain by a thick pile of Paleozoic sediments. Later tectonic modifications by backthrusting and hinterland-directed normal faulting as well as by Acadian strike-slip faulting substantially changed the geometry of the transported volcanic rocks and the structural style both across and along the strike of the orogen. The extension of the gravity anomaly under the St. Lawrence River also suggests that the Ordovician deformation front is 20 to 30 kilometers further to the north than previously interpreted.

Recent work in the Melville Peninsula area of the Rae Craton provides new constraints on the lithotectonic framework of Archean supracrustal rocks and associated Archean intrusions, as well as Paleoproterozoic cover sequences. The region is subdivided into four lithologically distinctive crustal blocks that include from north to south: the Northern Granulite Block; the Prince Albert Block; on which lies the Penrhyn Group; and the Repulse Bay Block. The Prince Albert belt is redefined as a ca. 3.20 Ga to 2.77 Ga greenstone belt, much older than the Committee Bay belt to which it was historically linked and collectively named the Prince Albert Group. On the eastern side of the Peninsula, the Roche Bay greenstone belt appears to be linked - at least in age - to the Prince Albert belt. Penetrative Paleoproterozoic deformation can be confidently documented northwesterly to the Roche Bay greenstone belt. Beyond this, it is less well defined although the Folster Lake Formation suggests moderate deformation under upper-greenschist metamorphic conditions.