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Metamorphism in the Upper Devonian of N. Cornwall

Published online by Cambridge University Press:  01 May 2009

F. Coles Phillips
F. Coles Phillips
Affiliation:
Fellow of Corpus Christi College, Cambridge.
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Extract

The geological succession and structure of the district are briefly summarized. Evidence of stress conditions becomes increasingly abundant as one passes from south to north towards the boundary of the Carboniferous.

The thermal alteration due to the Bodmin Moor granite is definitely delimited by tracing the outer limit of spotting in normal pelitic sediments.

Petrographical study of phyllites from outside this limit shows considerable mineralogical reconstruction in the sediments, with crystallization of white mica, chlorite and chloritoid; in some instances garnet is developed. The distribution of these types shows no relationship to the granite outcrop, but accords with the main structural features of the area.

Analogous changes are prominent in the igneous horizons, with the formation of schists of the general type of prasinite.

Within the aureole thermal effects can be traced superposed on the earlier dynamic changes.

From these lines of inquiry it is concluded that many of the changes in the phyllites, notably the formation of porphyroblastic white mica, chlorite and chloritoid, hitherto ascribed with greater or less finality to the action of the granite, are due to an earlier dynamic metamorphism.

Type
Original Articles
Information
Geological Magazine , Volume 65 , Issue 12 , December 1928 , pp. 541 - 556
Copyright
Copyright © Cambridge University Press 1928

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References

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