The style of deformation in the Devonian rocks on Hitra and Smøla, Central Norway.

Abstract

The Old Red Sandstone sequence in the Outer Trøndelag Region comprise conti-nental conglomerates, sandstones and mudstones of latest Silurian to MiddleDevonian age. During a Late Devonian tectonic phase (Solundian Phase) thedeposits were deformed and metamorphosed. The fold styles on Hitra and Smølaare quite different and probably represent different tectonic levels in acontinuous structure. Evidence of mesoscopic thrusting and near bedding-parallel mylonites indicates that the Devonian rocks have been involved insouth directed thrusting, which is compatible with deep-seismic reflectiondata. The metamorphic grade was close to the boundary of the anchizone andlower greenschist facies and pressures in the order of 4.1-4.8 kb are indi-cated. K-Ar dating of while micas shows that uplift and cooling took placein Late Devonian time.