Characterization of carbonate veins in graywacke layers from the Humber zone (Quebec, Canada) and implications for strength recovery of damaged rocks by mineral precipitation

Abstract

The Humber zone's Paleozoic sedimentary rocks, located on the rocky beaches of the Saint-Lawrence River in Quebec, Canada, exhibit interlayered calcareous greywacke beds and ductile shale. Fractures within these layers are characterized by either carbonate veins or barren joints, which are parallel arrays of planar fractures aligned in similar orientations. Fracture initiation occurred at either lithological interfaces or within brittle layers. The thickness of carbonate veins increases linearly with either bed thickness or layer-parallel extension strain, and carbonate precipitation occurred either simultaneously or ephemerally after the fracture opened. For a given bed thickness, veins are more closely and regularly spaced than joints, a feature that was successfully modeled using 2D finite element modeling. Both veins and joints follow a power-law relation between fracture spacing (s) and bed thickness (t), yielding a Weibull modulus of ∼2.5, a tensile strength of ∼9 MPa for the greywacke, and a shear flow strength of ∼1 MPa for the shale at the time of fracture formation. The different s-t relationships observed between joints and veins indicate that carbonate cementation results in 60% strength recovery for greywacke layers in the study area. This approach provides a new constraint on the degree of rock strength recovery due to mineral precipitation into opening fractures under natural conditions. The cementation-induced strength recovery inhibits stress axis permutation, and consequently, suppresses the formation of orthogonal veins.