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Department of Environmental Studies, University of Ulster at Jordanstown, Newtownabbey, Co. Antrim BT37 0QB, UK;
* Department of Geology, National Museum of Wales, Cathays Park, Cardiff CF1 3NP, UK;
Department of Geology, The University, Keele, Staffordshire ST5 5BG, UK
Lower Ordovician marine strata, formed in an ensialic marginal basin environment, record early episodes of distant explosive silicic volcanism and a later volcanotectonic episode which was a precursor to the development of a wide variety of near-to-source submarine silicic volcanic phenomena. The early episodes are represented by well-bedded turbiditic tuffs. These and older strata, at least 770 m thick in normal stratigraphical succession, are allochthonous, and large-scale wet-sediment sliding with reworking of strata in cohesive debris flows reflects major disturbance of the sea floor during the emplacement of silicic magmas. Volcanotectonic uplift along a N-S fault exceeded 1 km and led to the emergence and erosion of a rhyolitic volcanic island. This was followed closely by submergence, and in water depths perhaps of about 500 m there accumulated welded and non-welded rhyolitic ash-flow tuffs, rhyolitic turbiditic tuffs, rhyolite lavas and a wide variety of debris flow deposits. Shallow intrusions of 'low'-viscosity rhyolite were emplaced contemporaneously. The more or less simultaneous emplacement of rhyolitic tuff with both 'low'-viscosity and high-viscosity rhyolites is attributed to variable water content related perhaps to volatile fluxing in a magma body. The location of the near-to-source extrusive rocks and consanguineous intrusions along the contemporary N-S fault is considered to reflect channelling of magma, initially along a deep crustal fracture.
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 R. E. BEVINS, G. J. LEES, and R. A. ROACH Ordovician bimodal volcanism in SW Wales: geochemical evidence for petrogenesis of the silicic rocks Journal of the Geological Society, August 1, 1991; 148(4): 719 - 729. [Abstract] [PDF]
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 T. McCann Petrological and geochemical determination of provenance in the southern Welsh Basin Geological Society, London, Special Publications, January 1, 1991; 57(1): 215 - 230. [Abstract] [PDF]
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M. J. BRANNEY and R. S. J. SPARKS Fiamme formed by diagenesis and burial-compaction in soils and subaqeuous sediments Journal of the Geological Society, December 1, 1990; 147(6): 919 - 922. [Abstract] [PDF]
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M. J. BRANNEY Short Paper: The subaerial setting of the Ordovician Borrowdale Volcanic Group, English Lake District Journal of the Geological Society, December 1, 1988; 145(6): 887 - 890. [Abstract] [PDF]
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P. KOKELAAR Tectonic controls of Ordovician arc and marginal basin volcanism in Wales Journal of the Geological Society, October 1, 1988; 145(5): 759 - 775. [Abstract] [PDF]
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