Abstract

Major ring-intrusions in the Gardar Province are frequently elliptical in cross-section and are located at the intersections of regional dyke swarms with sinistral wrench-fault systems. Fault movement was contemporaneous with igneous intrusion and the ellipticity may be explained by ductile deformation of hot intrusions undergoing large-scale simple-shear.

Geometrical measurements on four of the intrusions give shear-strain values (γ) ranging from 0.6–1.2. Away from the intrusions, deformation is entirely by brittle fracture and the amount of fault movement correlates well with the sum of brittle and ductile movement within the intrusions.

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