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Magma rheology variations in sheet intrusions of the Ardnamurchan Central Complex (Scotland) inferred from gabbro inclusion characteristics

Gertisser, Ralf

Magma rheology variations in sheet intrusions of the Ardnamurchan Central Complex (Scotland) inferred from gabbro inclusion characteristics Thumbnail


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Abstract

Entrainment of xenoliths and their consequent assimilation are key processes in modifying the crystallization kinetics and magma dynamics of conduit systems. Here, an integrated textural and mineral chemical study of the evolution of a suite of gabbroic inclusions within a set of sheet intrusions from the Ardnamurchan Central Complex, NW Scotland, is presented. The key findings are as follows: (1) the host magma sheets and inclusions are not cognate; (2) there are microstructural and mineral chemical similarities between the gabbroic inclusions and the textures and mineralogy of the major Hypersthene Gabbro on Ardnamurchan; (3) orientations of magnetic fabrics within the host sheet groundmass and within the gabbroic inclusions are virtually identical. Field observations suggest that the inclusions were derived from the Hypersthene Gabbro and were entrained in a few laterally restricted magma segments that subsequently coalesced with inclusion-free segments into continuous sheets. Using Stokes’ Law and adaptations thereof, we calculate that the magma within the inclusion-free segments behaved as a Newtonian fluid, with a potential settling velocity of <0·028 m s–1. In contrast, the presence of gabbro inclusions probably modified the magma dynamics to Bingham-like behaviour. We infer that this variation in the magma rheology of separate segments continued after coalescence and internally partitioned the magma sheet, preventing lateral mixing and inclusion transport.

Journal Article Type Article
Acceptance Date Aug 28, 2012
Publication Date 2013-01
Publicly Available Date Mar 28, 2024
Journal Journal of Petrology
Print ISSN 0022-3530
Publisher Oxford University Press
Pages 75 - 102
DOI https://doi.org/10.1093/petrology/egs064
Keywords anisotropy of magnetic susceptibility, Ardnamurchan, magma rheology, inclusions, magma flow
Publisher URL https://doi.org/10.1093/petrology/egs064

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