The tectonic evolution of a Lewisian complex on Coll, Inner Hebrides

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Abstract
Synopsis: The heterogeneous Lewisian rocks of Coll show the effects of at least six phases of deformation. The absence of common, penetrative linear fabrics, and of representatives of the Scourie swarm of basic dykes, so useful in relative dating in most areas of Lewisian, limits rigorous analysis and regional correlation of tectonic events. To some extent the limitations have been overcome by examination of the effects of each phase on earlier structures, and of the geometry of the fold forms produced. Although some evidence points to earlier structures, the oldest decipherable event took place during granulite-facies metamorphism. Basic dykes were emplaced under the same conditions and were suitably modified. Since the intrusive episode the complex has been subjected to several tectonic episodes, each characterised by distinctive structural features. In each case, compositionally contrasted lithologies were affected in different ways. The rheological state of the whole complex is suggested to have varied during its evolution.