Time-constrained multiphase brittle tectonic evolution of the onshore mid-Norwegian passive margin

Abstract

Abstract The mid-Norwegian passive margin is a multiphase rifted margin that developed since the Devonian. Its geometry is affected by the long-lived activity of the Møre-Trøndelag fault complex, an ENE-WSW–oriented regional tectonic structure. We propose a time-constrained evolutionary scheme for the brittle history of the mid-Norwegian passive margin. By means of remote-sensing lineament detection, field work, microstructural analysis, paleostress inversion, mineralogical characterization, and K-Ar dating of fault rocks, six tectonic events have been identified: (1) Paleozoic NE-SW compression forming WNW-ESE–striking thrust faults; (2) Paleozoic NW-SE transpression forming conjugate strike-slip faults; (3) Carboniferous protorifting forming NW-SE– and NE-SW–striking faults; (4) Late Triassic–Jurassic (ca. 202 and 177 Ma) E-W extension forming approximately N-S–striking epidote- and quartz-coated normal faults and widespread alteration; (5) renewed rifting in the Early Cretaceous (ca. 122 Ma) with a NW-SE extension direction; and (6) Late Cretaceous extensional pulses (ca. 71, 80, 86, 91 Ma ago) reactivating preexisting faults and crystallizing prehnite and zeolite. Our multidisciplinary and multiscalar study sheds light onto the structural evolution of the mid-Norwegian passive margin and confirms the active role of the Møre-Trøndelag fault complex during the rifting stages. Our 62 new radiometric K-Ar ages define discrete episodes of faulting along the margin. The proposed workflow may assist in the interpretation of the structural framework of the mid-Norwegian passive margin offshore domain and also help to better understand fault patterns of fractured passive margins elsewhere.