A Petrographic and Geochemical Study of Back-Veining and Hybridization at a Gabbro-Felsite Contact in Coire Dubh, Rhum, Inverness-Shire

A. C. Dunham
Department of Geology, South Road, Durham

Summary: Field, petrographic, and chemical data are presented which make it possible to follow the course of back-veining of felsite by a gabbro ring-dyke. The remelted felsite back-veined the chilled margin of the gabbro, then acidified the partly crystalline basic mush within the chilled zone and finally mixed with the mainly liquid basic magma farther inside the dyke to produce hybrids of marscoitic aspect. Spectrographically determined trace-element data, with data on some major elements, illustrate these changes. The veins are shown to have a composition nearer the ternary minimum in the system Ab-Or-Qz-H2O than the parent felsite, while culminations of soda and iron in the acidified gabbros and hybrids suggest that metasomatism has accompanied the mixing of the partly liquid end members. This study confirms the earlier suggestion that the gabbro post-dates the felsite.

Mineralogical Magazine; June 1964 v. 33; no. 265; p. 887-902; DOI: 10.1180/minmag.1964.033.265.05
© 1964, The Mineralogical Society
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