The form, distribution and anisotropy of magnetic susceptibility of Jurassic dykes in H.U. Sverdrupfjella, Dronning Maud Land, Antarctica. Implications for dyke swarm emplacement

The Mesozoic dyke swarms of Western Dronning Maud Land, Antarctica, form a minor intrusive component of the Karoo large igneous province. Five-hundred and sixty one dykes were recorded intruding Neoproterozoic gneisses and Middle Jurassic syenite plutons. 40Ar/39Ar geochronology data reveal two temporally distinct components: the 178–175 Ma, alkaline, Straumsvola dyke swarm that predominantly intrudes a nepheline syenite pluton; and the 206–204 Ma, tholeiitic, Jutulrøra dyke swarm found throughout the study area. The Straumsvola swarm exhibits highly variably dyke trends that display a restricted opening direction, interpreted to be the result of high magma pressure equal to the maximum principal stress. The Jutulrøra swarm displays a fan of dyke trends, with dyke thickness and spacing increasing away from the inferred point of fan convergence. Anisotropy of magnetic susceptibility measurements reveal vertical magma transport within both dyke swarms in the Straumsvola area, with the southern/outer exposures of the Jutulrøra swarm exhibiting lateral magma transport. Although associated with a long-lived, local igneous centre comparison of palaeostress estimates for the Straumsvola dyke swarm and contemporaneous dykes in Ahlmannryggen and Vestfjella, indicates the presence of a regional scale radial stress system in western Dronning Maud Land between 178–175 Ma, supporting a mantle plume origin for the Karoo large igneous province.