The Moel-y-Golfa Andesite: An Ordovician (Caradoc) intrusion into unconsolidated conglomeratic sediments,Breidden Hills Inlier,Welsh borderland |
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| Authors: | R J Dixon |
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| Abstract: | The Moel-y-Golfa Andesite is a discordant intrusive body of porphyritic pyroxene andesite, 1 km across and at least 200 m thick. Textural variation defines a central facies and a marginal facies, the latter displaying well-formed lobes, tubes, and pillows. The vertically stacked lobes, brecciated tubes, and elongate pillows of andesite intrude and locally enclose enclaves of altered host sediment and are cut by steeply dipping slide scars. The host sediments are locally strongly silicified and cut by numerous, anastomosed vertical and subvertical fissures. Fissures are filled by disrupted host sediment and fragments of brecciated andesite. The formation and filling of each fissure system was probably concomitant with the brecciation of an intrusive magma lobe. The complex relationship of igneous and sedimentary material indicates that the Moel-y-Golfa Andesite was emplaced into the host sediments whilst they were unconsolidated or only partly lithified. |
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| Keywords: | Intrusive Andesite dome Lobes Pillows/tubes Fluidization Syn-emplacement slides Caradoc Welsh Basin |
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