New insights into the cone sheet structure of the Cuillin Complex, Isle of Skye, Scotland

Abstract

Abstract: Structural data were collected on 1100 cone sheets and dykes with the aim of reconstructing the geometry of the complex, recognizing emplacement phases, and contributing to understanding this classical area and the evolution of cone sheets in general. Mean sheet dip angles are 40°, 43°, 47° and 50° in four sections transecting the complex. Sheet thickness ranges from a few centimetres to 5 m, with a dominant thickness of <1 m. Intrusion intensity ranges from 1% to 35%, increasing towards the central zone. Initial cone sheet emplacement occurred within a gabbroid pluton that was hot enough to amalgamate the sheets. Dykes striking N155–165° were then emplaced, followed by shallow-dipping cone sheets, dykes striking N135–145°, steep-dipping cone sheets, dykes striking roughly east–west and, finally, dykes striking N150–165°. The NW–SE-striking dykes were emplaced during re-establishment of regional stresses, after perturbation by local magma-induced stresses when cone sheets were emplaced, interspersed with magma escaping horizontally from the volcano conduit to feed local dykes. Two successive magma chambers at different depths, with flat geometries and different volumes, may explain sheet architecture and location. The whole cone sheet system consists of a stack of parallel concentric sheets, rather than a model of convergence towards a single focus.