Scotland: geological foundations and landscape evolution

Scotland displays remarkable geological diversity, comprising igneous, sedimentary and metamorphic rocks that date back to the Archaean and span all the major periods of the geological timescale. This geodiversity reflects global plate tectonics, the position of Scotland near convergent and divergent plate margins at different times during its history, the drift of the Scottish landmass as a small part of larger continental entities across the surface of the globe through different morphoclimatic zones and depositional environments, and long-term changes in global climate and sea level. The Scottish landmass was essentially assembled ~425 Ma, from the amalgamation of the Laurentia and Baltica–Avalonia plates during the Caledonian Orogeny as the Iapetus Ocean closed. This brought together different crustal fragments comprising Archaean igneous and metamorphic rocks, and Proterozoic and Early Palaeozoic sedimentary and metasedimentary rocks. Orogenesis was accompanied by the emplacement of igneous intrusions, and uplift and erosion of the Caledonian mountain chain. Deposition of thick accumulations of terrestrial sediments during the Devonian was followed later by Palaeozoic and Mesozoic marine, deltaic and continental sedimentation and Palaeozoic igneous activity. During the Palaeogene, central igneous complexes and extensive lava fields formed in the Hebridean Igneous Province due to the presence of an underlying mantle plume that also initiated the opening of the North Atlantic Ocean to the west. The influence of this geodiversity is widely expressed in the geomorphology of the present landscape as a consequence of differential weathering and erosion, modulated by variable tectonic uplift, tilting and downwarping, mainly during post-Caledonian times and particularly during the Cenozoic.