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| Snowdon Volcanic Group | |
|---|---|
| Name | Snowdon Volcanic Group |
| Type | Volcanic group |
| Period | Ordovician |
| Primary lithology | Rhyolite, Andesite, Tuff |
| Other lithology | Ignimbrite, Breccia, Mudstone |
| Named for | Snowdon |
| Region | North Wales |
| Country | Wales, United Kingdom |
Snowdon Volcanic Group is an Ordovician volcanic succession exposed in northwestern Wales centered on Snowdon (mountain) and the Snowdonia National Park. The succession records felsic to intermediate volcanism related to the Caledonian orogeny and is integral to regional studies by institutions such as the British Geological Survey and universities in Cardiff University and Bangor University. It is interleaved with sedimentary units studied alongside formations like the Bala Group and correlated with terranes recorded in the Lake District and Moesian Platform literature.
The Group comprises volcanic and volcaniclastic rocks deposited during the Late Ordovician as part of the Avalonian-Cadomian-Caledonian tectono-magmatic system, linking stratigraphic interpretations used in comparisons with the Borrowdale Volcanic Group, Llanberis Slates, Harlech Dome and sequences in the Southern Uplands. Regional mapping by the Geological Society of London and fieldwork by researchers affiliated with the Natural History Museum, London situates the unit within the lithotectonic framework that also includes terranes studied in the Ireland and Scotland correlations.
Stratigraphically the unit overlies older Cambrian and early Ordovician strata and is succeeded locally by mudstone and sandstone packages comparable to the Gwna Group and Arenig sediments; these relationships have been interpreted in syntheses published in journals associated with the Royal Society. Lithologies include rhyolitic lavas, andesitic flows, welded tuffs, ignimbrites, and volcaniclastic breccias analogous to sequences in the Keila Formation and Skiddaw Group. Primary facies descriptions reference particular exposures at Llanberis Pass, Rhyd Ddu, and the Hafod y Llyn area, with accessory mineralogy compared to samples curated at the National Museum Cardiff.
Geochemical analyses, including major- and trace-element systematics and isotopic studies comparable to methods used in work on the Serranias Merida and Sierra Nevada (Spain), indicate calc-alkaline to peraluminous affinities consistent with subduction-related magmatism. Radiometric ages obtained by teams collaborating with laboratories such as University College London and the Open University align the volcanism with the Late Ordovician (Caradoc-Ashgill) interval, and isotopic work ties the rocks to regional metamorphic episodes recognized in the Caledonian orogeny sequence and comparisons with radiometric datasets from the Grampian Highlands.
The volcanic activity is interpreted within a convergent margin context during closure of oceanic domains recognized in tectonic syntheses alongside the Iapetus Ocean and collision events recorded by the Scandian phase and continental accretion documented in the Acadian orogeny literature. Field relations demonstrate episodic explosive eruptions, effusive flow emplacement, and coeval sedimentation similar to volcanic arcs described from the Andes and ancient arcs preserved in the Appalachians. Structural overprints related to the later Caledonian deformation—mapped and modeled by researchers at the University of Edinburgh and the University of Manchester—produce folding, cleavage development, and localized metamorphism comparable to features in the Bentonite-bearing horizons of other British successions.
Key exposures occur across the Gwynedd area and include classic localities at Snowdon (mountain), Rhydd Ddu, Llanberis Pass, and the Moel Hebog region, where classic field descriptions used in field guides by the Geological Society of London illustrate contacts with the Ffestiniog and Conwy area sequences. Correlative outcrops extend to inliers mapped near Caernarfon and are used in educational field trips run by departments at Imperial College London and University of Leeds for comparative studies with the Lake District volcanics.
Although not a mineralization focus like the Conwy Bay lead-zinc deposits, the Group supplies construction stone and roadstone locally and is part of landscape and geotourism resources promoted by Cadw and the Snowdonia National Park Authority. Paleoenvironmental reconstructions using proxy data analogous to studies involving the Paleobiology Database and paleomagnetic datasets from institutions such as the British Antarctic Survey inform models of Ordovician climate and biotic change correlated with biostratigraphic markers used in trilobite and graptolite research at museums like the Natural History Museum, London and academic collections at University College Dublin.
Category:Geology of Wales Category:Ordovician volcanism