Basement-influenced rifting and basin development: a reappraisal of post-Caledonian faulting patterns from the North Coast Transfer Zone, Scotland

Abstract

AbstractThe post-Caledonian development of the West Orkney Basin is regularly cited as a classic example of basement-influenced rifting. This paper presents the first detailed multidisciplinary analysis of the three-dimensional (3D) geometries and distribution of post-Caledonian faults in onshore northernmost Scotland, examining their relationships to basement fabrics and comparing them to rift-related structures developed offshore in the West Orkney Basin. Two phases of rift-related faulting are distinguished: 1) Devonian ENE–WSW extension localized in the east of the basin and related to regional sinistral transtension along the Great Glen Fault; and 2) Permo-Triassic NW–SE extension focused to the west of the basin and probably contemporaneous with movements along the Minch Fault. A complex North Coast Transfer Zone is developed along the northern Scottish coast linking Mesozoic rifts that reactivated Caledonian structures in the West Orkney Basin (Naver Thrust) to those bounding the North Minch Basin (Outer Hebrides Fault Zone). Polymodal faulting patterns are widespread in onshore exposures. Fault patterns vary due to changes in the obliquity between regional rifting vectors and variably orientated pre-existing structures in each basement terrane. The geometric complexity and spatial variations in fault patterns onshore can be correlated with changes in basement structures, despite limited direct reactivation of pre-existing fabrics.