Challenges of structural diagenesis in foreland fold-and-thrust belts: A case study on paleofluid flow in the Canadian Rocky Mountains West of Calgary

Foreland fold-and-thrust belts are challenging because their structural complexity highly impacts fluid flow and diagenetic processes. Paleofluid flow in the Rocky Mountain fold-and-thrust belt west of Calgary was investigated following a structural diagenetic approach. Paleofluid flow or mass transfer mechanisms have been inferred based on vein morphology (completely filled, en echelon, slickenfibre, bed-parallel, open or micro-breccia veins), orientation and geochemistry (stable oxygen and carbon isotope and strontium isotopes). Bed-parallel veins probably developed by flexural slip during Laramide folding, and most completely filled and slickenfibre veins formed or were reactivated during the Laramide Orogeny. Both types of veins associated with the Laramide Orogeny precipitated under low fluid flux conditions, dominated by diffusional processes as inferred from stable isotopic signatures similar to the host rock. The open veins with meteoric calcite cement, marked by cathodoluminescence zonations and strongly depleted oxygen isotopic signature, point to advectional fluid flow processes in a post-Laramide extensional stress field. Some slickenfibre and completely filled veins that originally formed during the compressional phase of the Laramide Orogeny were probably reactivated at time of the open vein formation. The latter inference is based on the occurrence of the same cement in the open veins as in the centre of the slickenfibre and completely filled veins. In conclusion, there is no evidence for large-scale fluid flow during the Laramide Orogeny, but evidence points to post-Laramide large-scale fluid advection being prevalent. Challenges in this structural diagenetic study consist of (i) the lack of abundant vein–vein and vein-stylolite cross-cutting relationships in the outcrops studied, (ii) the difference between structural versus diagenetic concepts, (iii) the uncertainty of chronology and attribution of fracture sets and diagenetic cements to either a single or discrete episodes, and (iv) reactivation of veins.

► Different vein types were analysed using a structural diagenetic approach.
► Fluid flow evolution in the Canadian Rocky Mountains study area was reconstructed.
► Most veins are related to low fluid flux during the Laramide Orogeny.
► Open veins are associated with post-Laramide large-scale meteoric fluid advection.