The tectono‐magnetic signature of the old red sandstone and pre‐Devonian strata in the HÅSteinen Area, western Norway, and implications for the later stages of the Caledonian Orogeny

Abstract

The structural fabrics recorded from Devonian rocks and substrate in the Håsteinen area, Western Norway, show near E‐W trends. In the Devonian rocks these fabrics are a consequence of post‐depositional regional folding at a considerable depth, presumably attended by the aquisition of an thermoviscous (TVRM) or thermochemical (TCRM) remanence (group A). Post or possibly late syntectonic group A remanences (declination=210, inclination = +18, α95=9) constitute the principal remanence in both Devonian rocks and their substrate, whereas a younger group B magnetization (declination=047, inclination=+59, α95=7) relates to early Mesozoic shearing. The palaeomagnetic (group A) and structural data from the Håsteinen and Kvamshesten Old Red Sandstone Massifs favor a regional compressive N‐S shortening event (Svalbardian‐Solundian), which probably occurred during latest Devonian times. Some recent extensional‐basin models, appealing to listric‐normal faulting to account for both the sedimentation and the subsequent deformation of the Western Norwegian Devonian rocks, are rejected on the basis of inadequate structural information.