The Rhum layered complex, Inner Hebrides, Scotland

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Authors:Emeleus, C. H.
Author Affiliations:Primary:
Univ. Durham, Dep. Geol. Sci., Durham, United Kingdom
Volume Title:Origins of igneous layering
Volume Authors:Parsons, Ian, editor
Source:NATO Advanced Study Institutes Series. Series C: Mathematical and Physical Sciences, Vol.196, p.263-286; NATO Advanced Research Workshop on Origins of igneous layering, Narsarsuaq, Greenland, Aug. 4-15, 1986, edited by Ian Parsons. Publisher: D. Reidel Publishing Company, Dordrecht-Boston, International. ISSN: 0377-2071
Publication Date:1987
Note:In English. 49 refs.; illus. incl. 2 tables, sect., geol. sketch map
Summary:The Lower Eocene Rhum central complex has a core of ultrabasic rocks and gabbros which formed at a late stage in the centre's evolution. Three major components are: the eastern layered series of alternating layers (= or <80 m thick) of feldspathic peridotite and allivalite <600 m thick; the western layered series of layered gabbros conformably overlain by layered feldspathic peridotites; and a later intrusive central series of feldspathic peridotites and subordinate gabbros, dunites and layered allivalites. The central series contains abundant ultrabasic breccias. Emplacement of the ultrabasic and gabbroic rocks was initially controlled by the main ring fault but the Long Loch fault zone exercised control during intrusion of the central series. The eastern and western layered series are parts of a once-continuous steep-sided intrusion with a domed roof that extended only slightly above the level of the Rhum mountains (approx 800 m altitude). The Rhum parental magmas were olivine-rich picrite or ultrabasic with basaltic magmas. The field relations strongly suggest that the magmas crystallized at the levels at which ultrabasic rocks and gabbros now occur. Layering in the eastern layered series is attributed to injection of pulses of picritic magma which ponded beneath more evolved, lighter and cooler residual magma and above allivalitic cumulates. Crystallization of each new batch gave a layer of peridotite and the residual liquid mixed with earlier, evolved residual magma from previous batches to form allivalite, building up the layered succession of 16 major peridotite/allivalite units. Gravity studies on Rhum show that the mafic rocks are the top of a dense body at least 15 km in vertical extent. Small-scale and possibly larger-scale replacement of allivalite by peridotite occurred and migration of intercumulus magma from layer to layer was largely responsible for this replacement. Emplacement of the mafic magmas into acidic country rocks caused anatexis and the formation of marginal intrusion breccias. Melted country rocks probably also mixed with the magmas resulting in the contamination in some of the gabbros and allivalites. [A.W.H.]
Subjects:Cenozoic; Chemical composition; Differentiation; Emplacement; Eocene; Fractional crystallization; Gabbros; Igneous rocks; Intrusions; Layered intrusions; Lower Eocene; Magmas; Mineral composition; Paleogene; Petrology; Plutonic rocks; Tertiary; Ultramafics; Europe; Great Britain; Hebrides; Highland region Scotland; Inner Hebrides; Inverness-shire Scotland; Rhum; Scotland; United Kingdom; Western Europe; Central Series; Eastern Layered Series; Rhum Complex; Western Layered Series
Coordinates:N365000 N370500 W0062500 W0063000
Abstract Numbers:88M/1193
Record ID:1988015655
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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