Igneous emplacement in a shear-zone termination: The biotite granite at Strontian, Scotland
Deformed xenolith (strain) data together with other structural information indicate that the biotite granite body (∼90 sq km) of the Strontian complex, Scotland, was emplaced in the extensional termination of a dextral transcurrent shear zone. This shear zone is a splay of the major Great Glen fault which lies along the southern boundary of the granite. Siting of the shear zone splay was probably controlled by (a) a slight releasing bend in the Great Glen fault in this area and (b) a large, pre-existing, asymetric synform in Proterozoic metasedimentary country rocks which intersects the Great Glen fault trace at a high angle. A model is proposed in which Moine Thrust (Caledonian) compression at ca. 435 Ma activated the Great Glen fault dextrally. Dextral movements around the releasing bend detached a flat segment from the inside fault wall, and the biotite granite was emplaced side-ways at depths of about 15 km as a sheet into this extensional, listric-fault-bounded, cavity.