Palaeomagnetic dating of brittle tectonics structures: case studies on Ferques fault (Boulonnais, France) and two faults from the holy cross mountains (Poland)

Abstract

Calcite and sedimentary fills in fractures cutting the Upper Devonian carbonates in the Holy Cross Mountains (HCM) and Boulonnais (B) were dated palaeomagnetically by comparison with the Apparent Polar Wander Path (APWP) for Baltica in order to constrain age of faults. Here we present results obtained from calcite and sedimentary fills of two selected faults as case studies. Hematite-bearing elastics and calcite possessed well-defined components of natural remanent magnetization (NRM) that were preserved up to thermal demagnetization at ca. 500 °C. Two components in Rzepka calcite (HCM) and one component residing in elastics within Ferques Fault (B) could be determined. Comparison of directions of these components with reference directions calculated from the APWP for Baltica constrains the upper age limit for the Ferques Fault to Middle Triassic, while Rzepka and Jazwica faults may be no younger than Late Permian. Generally, the remanence from fracture fills may be useful for dating related tectonics, karst phenomena or mineralization processes.