Infiltration metasomatism of cumulates by intrusive magma replenishment; the Wavy Horizon, Isle of Rum, Scotland

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doi: 10.1093/petrology/eg1072
Authors:Holness, M. B.; Hallworth, M. A.; Woods, A.; Sides, R. E.
Author Affiliations:Primary:
University of Cambridge, Department of Earth Sciences, Cambridge, United Kingdom
Other:
BP Institute, United Kingdom
Volume Title:Journal of Petrology
Source:Journal of Petrology, 48(3), p.563-587. Publisher: Oxford University Press, Oxford, United Kingdom. ISSN: 0022-3530
Publication Date:2007
Note:In English. 42 refs.; illus., incl. 3 plates, 6 tables, geol. sketch map
Summary:The Eastern Layered Intrusion of the Rum Layered Suite comprises paired peridotite and allivalite (troctolite and gabbro) layers forming 16 macro-rhythmic units. Whereas the majority of these macro-units are believed to have formed by a process of crystal-liquid differentiation involving successive accumulation of crystals from multiple picritic replenishments of the chamber, the Unit 9 peridotite is interpreted as a layer-parallel picrite intrusion. Closely correlated with this discontinuous peridotite body is a distinctive feature generally known as the Wavy Horizon, which divides the overlying allivalite into a lower troctolite and an upper gabbro along a well-defined undulating contact. We propose that the Wavy Horizon is a metasomatic feature formed consequent to the removal of clinopyroxene from an original gabbroic mush. Foundering of the mush into the picritic sill resulted in the replacement of the original interstitial liquid by one saturated only in olivine (± plagioclase). Progressive through-flow of this liquid resulted in the stripping out of clinopyroxene from the lower parts of the allivalite. We interpret the Wavy Horizon as a reaction front, representing the point at which the invading liquid became saturated in clinopyroxene. The distinctive pyroxene-enriched zone immediately above the Wavy Horizon could have formed when mixing of the interstitial liquids on either side of the reaction front formed a supercooled liquid oversaturated in pyroxene, as a result of the curvature of the olivine-plagioclase-clinopyroxene cotectic. The presence of many such approximately layer-parallel features, defined by differences in pyroxene content, in the Eastern Layered Intrusion of Rum suggests that such an infiltration-reaction process was not unique to Unit 9.
Sections:Petrology
Subsections:Igneous petrology
Subjects:Cumulates; Gabbros; Igneous rocks; Infiltration; Intrusions; Layered intrusions; Magmas; Metasomatism; Peridotites; Plutonic rocks; Troctolite; Ultramafics; Europe; Great Britain; Hebrides; Highland region Scotland; Inner Hebrides; Inverness-shire Scotland; Rhum; Scotland; United Kingdom; Western Europe; Eastern Layered Intrusion; Rum layered Suite; Wavy Horizon
Coordinates:N565500 N570500 W0061500 W0063000
Abstract Numbers:07M/1061
Record ID:2007053065
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute.
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