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Robinson, D., Nicholls, R. A., Thomas, L. J. (1980) Clay mineral evidence for low-grade Caledonian and Variscan metamorphism in south-western Dyfed, south Wales. Mineralogical Magazine, 43 (331) 857-863 doi:10.1180/minmag.1980.043.331.06

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Reference TypeJournal (article/letter/editorial)
TitleClay mineral evidence for low-grade Caledonian and Variscan metamorphism in south-western Dyfed, south Wales
JournalMineralogical MagazineISSN0026-461X
AuthorsRobinson, D.Author
Nicholls, R. A.Author
Thomas, L. J.Author
Year1980 (September)Volume43
Issue331
PublisherMineralogical Society
Download URLhttps://rruff.info/doclib/MinMag/Volume_43/43-331-857.pdf+
DOIdoi:10.1180/minmag.1980.043.331.06Search in ResearchGate
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Mindat Ref. ID3157Long-form Identifiermindat:1:5:3157:2
GUID0
Full ReferenceRobinson, D., Nicholls, R. A., Thomas, L. J. (1980) Clay mineral evidence for low-grade Caledonian and Variscan metamorphism in south-western Dyfed, south Wales. Mineralogical Magazine, 43 (331) 857-863 doi:10.1180/minmag.1980.043.331.06
Plain TextRobinson, D., Nicholls, R. A., Thomas, L. J. (1980) Clay mineral evidence for low-grade Caledonian and Variscan metamorphism in south-western Dyfed, south Wales. Mineralogical Magazine, 43 (331) 857-863 doi:10.1180/minmag.1980.043.331.06
In(1980, September) Mineralogical Magazine Vol. 43 (331) Mineralogical Society
Abstract/NotesSummaryIllite crystallinity determinations on Palaeozoic pelitic rocks, whose stratigraphic range runs from Lower Cambrian to Westphalian, indicate that anchimetamorphism has affected both the Lower and Upper Palaeozoic sequences. Two metamorphic episodes are in evidence, with the earlier, Caledonian, being of slightly higher grade. The higher anchizone crystallinity values are recorded from the Fishguard area in which mineral assemblages of the prehnite-pumpellyite facies have recently been recognized in basic igneous rocks. The later metamorphic episode has affected rocks to the south of the Variscan front. Here crystallinity values are low anchizone but some straddle the boundary with the diagenetic state. The Pembroke coalfield lies in this southern area and has coals largely of anthracite rank with volatile matter contents of between 10.1 and 5% Grade of metamorphism as indicated by crystallinity and by coal rank data from the Pembroke coalfield shows anomalous results to that described from the main South Wales coalfield. A neo-formed 2M illite from the Variscan spaced cleavage is described with analytical and X-ray diffraction data.


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