Disruption of Dalradian stratigraphy along the Portsoy Lineament from new geological and magnetic surveys

Abstract

Synopsis Intrusions, metavolcanic rocks and metasediments which crop out along a zone defining the Portsoy Lineament in the Cabrach area have a well-defined magnetic signature. Multidisciplinary surveys have revealed the regional scale of dislocations within the zone evidenced by the juxtaposition of contrasting Appin and Argyll Group successions. To the west of the lineament a metasedimentary sequence extending from the Blair Atholl to the Easdale Subgroup is correlated with established Dalradian successions to the south. Within and to the east of the lineament, distinctive metasedimentary and metavolcanic sequences have Argyll Group characteristics but cannot be correlated with the western succession. Further east these rocks pass into Southern Highland Group lithologies without the intervening calcareous beds which characterise this part of the Dalradian elsewhere. Major mafic and ultramafic intrusions are confined to the area within and to the east of the lineament and are commonly bounded by shear zones. The major dislocations in this area support the concept of a decoupled NE Grampian regional block and the fundamental role of the Portsoy Lineament in controlling basin development and subsequent tectonic, metamorphic and igneous events.