Carbonatite-mantle interaction; a possible origin for megacryst/xenolith suite in Scotland

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Authors:Long, A.; Menzies, M. A.; Thirlwall, M.; Upton, B.; Aspen, P.
Author Affiliations:Primary:
University of London, London, United Kingdom
University of Brasilia, Brazil
Volume Title:Kimberlites, related rocks and mantle xenoliths
Volume Authors:Meyer, Henry O. A., editor; Leonardos, Othon H.
Source:CPRM - Special Publication, Vol.1A, p.467-477; Fifth international kimberlite conference, Araxa, Brazil, June 18-July 4, 1991, edited by Henry O. A. Meyer and Othon H. Leonardos. Publisher: Companhia de Pesquisa de Recursos Minerais, Rio de Janeiro, Brazil
Publication Date:1994
Note:In English. 51 refs.; illus.
Summary:A basic dyke from the Archaean craton of NW Scotland contains abundant lherzolites, pyroxenites and a wide variety of megacrysts. The more magnesian megacrysts appear to have 'co-existed' with a fluid rich in Ba, Nb, the LREE and Sr but with a low Rb/Sr ratio. This fluid had a very high [Ce/Yb]N ratio similar to magnesio-carbonatite melts but different from alkaline basalts believed to have co-existed with megacrysts from off-craton areas of Scotland. Carbonatite-mantle interaction transformed a peridotite protolith from an anhydrous residue, with low Rb/Sr and high Sm/Nd, to a complex assemblage of enriched peridotites and pyroxenites with variable Rb/Sr and low Sm/Nd ratios. Interaction appears to have occurred in the late Archaean or early Proterozoic (i.e. 2300-2500 m.y.) perhaps related to accretion of Proterozoic mobile belts. Time-integration of the elemental variability in such metasomatised mantle over the last 2500 m.y. has generated an enriched lithosphere source with the characteristics of Enriched Mantle 1 (EMI). The Loch Roag xenolith suite has many parallels, both petrologically and geochemically, with the apatite-rich mantle xenoliths from Kiama, Southern Highlands Province, Australia. These apatite-amphibole pyroxenite xenoliths are enriched in the LREE and the LIL elements, but exhibit a narrow range in both 87Sr/86Sr and143Nd/144Nd, and have been interpreted as the crystallization products from a modern kimberlitic/carbonatitic melt. [K.A.R.]
Subjects:Carbonatites; Chemical composition; Genesis; Igneous rocks; Inclusions; Isotopes; Lherzolite; Major elements; Mantle; Megacrysts; Mineral composition; Peridotites; Petrology; Plutonic rocks; Pyroxenite; Ultramafics; Xenoliths; Europe; Great Britain; Scotland; United Kingdom; Western Europe
Abstract Numbers:96M/1011
Record ID:1998020380
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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