Magma RheologyVariations in Sheet Intrusions of the Ardnamurchan Central Complex (Scotland) Inferred from Gabbro Inclusion Characteristics

Research output: Contribution to journalArticle

Authors

  • Craig Magee
  • Brian O'driscoll
  • Michael S. Petronis
  • P Clay
  • Ralf Gertisser

Colleges, School and Institutes

External organisations

  • Keele Univ
  • Univ Manchester
  • Keele Univ
  • IMPERIAL COLLEGE

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.

Details

Original languageEnglish
Pages (from-to)75-102
JournalJournal of Petrology
Volume54
Issue number1
Early online date13 Oct 2012
Publication statusPublished - 2013