Late Precambrian foliated plutonic complexes of the Channel Islands and La Hague; early Cadomian plutonism

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Authors:Power, G. M.; Brewer, T. S.; Brown, Michael; Gibbons, Wes
Author Affiliations:Primary:
Portsmouth Polytech., Dep. Geol., Portsmouth, United Kingdom
Other:
Univ. Nottingham, United Kingdom
Kingston Polytech., United Kingdom
Univ. Wales at Cardiff, United Kingdom
Volume Title:Cadomian Orogeny
Volume Authors:D'Lemos, R. S., editor; Strachan, R. A.; Topley, C. G.
Source:Geological Society Special Publications, Vol.51, p.215-229; The Cadomian Orogeny, Oxford, United Kingdom, Apr. 1988, edited by R. S. D'Lemos, R. A. Strachan and C. G. Topley. Publisher: Geological Society of London, London, United Kingdom. ISSN: 0305-8719
Publication Date:1990
Note:In English. 24 refs.; illus. incl. geol. sketch maps
Summary:The foliated granitic rocks of Guernsey, Sark and Alderney and on the nearby French mainland at La Hague are predominantly quartz diorites but with some granodiorite and minor granite. Greenschist facies metamorphism has affected some of these rocks; isotopic age data are unsatisfactory but suggest a possible age span of 700-580 m.y. Geochemical analyses for 168 rocks show that these granitic rocks are calc-alkaline, the majority being metaluminous with Na2O > K2O, and that they have the characteristics of normal volcanic arc granites. There are minor differences in the trace elements for the four areas; REE plots for 34 rocks all show strong fractionation of LREEs regardless of rock composition and most show HREE depletion. These patterns are interpreted as originating in the source and are taken to suggest an origin by high-P melting of predominantly basaltic compositions. The evidence supports a model for a major period of Cadomian crustal growth by progressive cratonization of a basin and arc system. [R.A.H.]
Subjects:Cadomian Orogeny; Chemical composition; Emplacement; Geochemistry; IGCP; Igneous rocks; Major elements; Metals; Orogeny; Plutonic rocks; Precambrian; Processes; Rare earths; Structural geology; Tectonics; Trace elements; Upper Precambrian; English Channel Islands; Europe; France; Normandy; United Kingdom; Western Europe; La Hague
Abstract Numbers:90M/3402
Record ID:1991029953
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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