A multidisciplinary investigation of multiple remagnetizations within the Southern Canadian Cordillera, SW Alberta and SE British Columbia

Abstract

AbstractAn integrated palaeomagnetic, geochemical and petrographic study was conducted on two folds in the Front Range of the Southern Canadian Cordillera in order to better understand the timing and origin of chemical remanent magnetizations (CRMs) relative to orogenesis. The folds are contained within Mississippian carbonates (330–335 Ma) which contain a pervasive pre-tilting to early syn-tilting Early Cretaceous, high-temperature CRM residing in magnetite. An intermediate-temperature CRM is a late syn-tilting to post-tilting, possibly Tertiary remagnetization, residing in pyrrhotite. A fluid conduit test (FCT) conducted on bedding-parallel veins shows that they are associated with the magnetite CRM, whereas late-stage tensile veins show a relationship to a pyrrhotite CRM. Elevated 87Sr /86Sr data indicate alteration by fluids with a radiogenic signature; along with the FCT results, these data are consistent with the interpretation that the magnetite CRM formed as a result of hydrocarbons and/or evolved basinal fluids that migrated ahead of the deformation front. Based on the presence of sulphur-enriched bitumen, barite and sphalerite, common by-products of thermal sulphate reduction (TSR), the pyrrhotite CRM is interpreted to be the result of late-stage TSR caused by warm basement fluids which moved along faults and fractures.