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Basic and ultrabasic volcanic rocks from the Argyll Group (Dalradian) of NE Scotland.

Macdonald, R. and Fettes, D. J. and Stephenson, D. and Graham, C. M. (2005) Basic and ultrabasic volcanic rocks from the Argyll Group (Dalradian) of NE Scotland. Scottish Journal of Geology, 41 (2). pp. 159-174. ISSN 0036-9276

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Abstract

The Dalradian Supergroup of the Scottish Highlands is a largely metasedimentary succession of Neoproterozoic to Early Cambrian age, metamorphosed during the Caledonian Orogeny. The rocks were deposited on the Laurentian margin during and following the break-up of Rodinia. This rift setting is evidenced, in the upper half of the succession, by the presence of several volcanic sequences. A significant development of these volcanic rocks occurs in the NE Grampian Highlands. There, the Blackwater Formation, within the Argyll Group of the Huntly area, is dominated by basic and ultrabasic metavolcanic rocks, with intercalated metasedimentary rocks. The rocks were metamorphosed in the amphibolite facies, with the Mg contents of their dominant amphiboles apparently reflecting those of the whole-rock protoliths. The protoliths ranged from ultrabasic picritic types (MgO up to 35 wt%) through high-magnesia basalts to basaltic andesites and andesites. The magmas feeding the volcanism were of tholeiitic affinity, broadly similar to metavolcanic rocks elsewhere in the Dalradian. Higher-Nb and lower-Nb groups can be distinguished. The inferred parental magmas were basalts with MgO c. 10 wt%. The ultrabasic rocks formed by accumulation of olivine and minor Cr-spinel within the parental basalts. Some more evolved rocks show evidence of minor (5–10 wt%) accumulation of Fe–Ti oxides. Primary magmas of the Blackwater metavolcanic rocks were generated from a mantle source, or sources, relatively enriched compared to the MORB source. It is speculated that all the Dalradian metavolcanic rocks represent varying degrees of mixing of magmas from this source and a depleted, MORB-like, mantle source.

Item Type: Article
Journal or Publication Title: Scottish Journal of Geology
Subjects: G Geography. Anthropology. Recreation > GE Environmental Sciences
Departments: Faculty of Science and Technology > Lancaster Environment Centre
VC's Office
Faculty of Science and Technology > Physics
ID Code: 21266
Deposited By: ep_ss_importer
Deposited On: 07 Jan 2009 11:55
Refereed?: No
Published?: Published
Last Modified: 26 Jul 2012 15:44
Identification Number:
URI: http://eprints.lancs.ac.uk/id/eprint/21266

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