Paleomagnetic dating of fracturing using breccia veins in Durness group carbonates, NW Scotland

A paleomagnetic study of red fault-related breccia veins in the Cambro-Ordovician Durness Group in NW Scotland was conducted to determine the time of brecciation, the origin of the veins, and the nature and timing of associated fluid-related diagenetic alteration. The veins contain brecciated fragments of the host Durness Group and strike either east–west or north–south. Clasts of breccia cemented by calcite suggest multiple brecciation events. The host Durness Limestone is a gray dolomite and contains a Devonian chemical remanent magnetization (CRM) that resides in magnetite. The veins contain magnetizations that reside in hematite and are interpreted as CRMs. The breccias in north–south veins contain a Triassic CRM whereas the veins with east–west strikes contain a Jurassic CRM. Authigenic hematite is common in the breccias along growth planes in the calcite cements. The two CRMs within the veins are interpreted as dating two separate brecciation and fluid flow events that precipitated authigenic hematite. The brecciation and fluid flow events are interpreted to be related to extension in the Mesozoic which is consistent with the extensional history of the northern Atlantic margins.