Analysis of Fracturing in Precambrian Volcanics North of Madoc, Ontario

This paper presents a study of joints and other systematic fractures in Precambrian metavolcanic rocks. Although the mechanism that created the complex array of joints is not clear, one can deduce that they served as pre-existing planes of weakness during a later period of deformation in which slip occurred along both joints and systematic fractures. One consequence of this movement was an adjustment of rock material at the junction of intersecting fractures. An 'adjustment surface' was created at specific fracture intersections by movement of adjacent joint blocks toward one another. This 'adjustment feature' is a structural element, which can be utilized in reconstructing the principal stress directions of the later period of deformation.