Nature and origin of layering in the diorites of SE Jersey, Channel Islands

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doi: 10.1144/gsjgs.140.6.0921
Authors:Bishop, A. C.; Key, C. H.
Author Affiliations:Primary:
Br. Mus., London SW7 5BD, United Kingdom
Volume Title:Journal of the Geological Society of London
Source:Journal of the Geological Society of London, 140(6), p.921-937. Publisher: Geological Society of London, London, United Kingdom. ISSN: 0016-7649
Publication Date:1983
Note:In English. 2 p. refs.; illus. incl. sketch map, strat. col.
Summary:These Cadomian diorites contain both primary gabbroic layering formed as igneous cumulates in a gabbroic magma, and differentiated diorite sheet-layering, developed from gabbroic layering during metasomatic alteration of gabbro to diorite (probably by hydrous fluid associated with granite emplacement). Primary gabbroic layering is preserved in a small area near Le Nez, showing many of the textures and structures typical of primary layering. The differentiated diorite sheets have the same orientation as the primary layers and each grades upwards from meladiorite to leucodiorite or quartz diorite. Chemical analyses are given for 13 gabbros and 18 diorites, together with electron probe analyses of 3 clinopyroxenes and 21 amphiboles; chemical variation within the differentiated sheets suggests that there was considerable modification of the original gabbro. The most basic part of the sheets occurs several tens of cm above the base, because of reaction across the quartz diorite-meladiorite boundary. The layered diorites originated by metasomatic alteration of layered gabbro rather than having formed as cumulates in a primary dioritic magma. [R.A.H.]
Subjects:Amphibole group; Cadomian Orogeny; Chain silicates; Diorites; Electron probe data; Gabbros; Igneous rocks; Intrusions; Layered intrusions; Major elements; Metasomatism; Petrology; Plutonic rocks; Recrystallization; Silicates; English Channel Islands; Europe; Jersey; United Kingdom; Western Europe; Cadomian; Le Nez
Abstract Numbers:84M/2020
Record ID:1986007760
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom, Reference includes data from PASCAL, Institute de l'Information Scientifique et Technique
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