Structural signatures of igneous sheet intrusion propagation

Craig Magee (Corresponding Author), James Muirhead, Nick Schofield, Richard J. Walker, Olivier Galland, Simon Holford, Juan Spacapan, Christopher A-L. Jackson, William McCarthy

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Abstract

The geometry and distribution of planar igneous bodies (i.e. sheet intrusions), such as dykes, sills, and inclined sheets, has long been used to determine emplacement mechanics, define melt source locations, and reconstruct palaeostress conditions to shed light on various tectonic and magmatic processes. Since the 1970's we have recognised that sheet intrusions do not necessarily display a continuous, planar geometry, but commonly consist of segments. The morphology of these segments and their connectors is controlled by, and provide insights into, the behaviour of the host rock during emplacement. For example, tensile brittle fracturing leads to the formation of intrusive steps or bridge structures between adjacent segments. In contrast, brittle shear faulting, cataclastic and ductile flow processes, as well as heat-induced viscous flow or fluidization, promotes magma finger development. Textural indicators of magma flow (e.g., rock fabrics) reveal that segments are aligned parallel to the initial sheet propagation direction. Recognising and mapping segment long axes thus allows melt source location hypotheses, derived from sheet distribution and orientation, to be robustly tested. Despite the information that can be obtained from these structural signatures of sheet intrusion propagation, they are largely overlooked by the structural and volcanological communities. To highlight their utility, we briefly review the formation of sheet intrusion segments, discuss how they inform interpretations of magma emplacement, and outline future research directions.
Original languageEnglish
Pages (from-to)148-154
Number of pages7
JournalJournal of Structural Geology
Volume125
Early online date21 Jul 2018
DOIs
Publication statusPublished - Aug 2019

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Keywords

  • Magma
  • Sheet intrusion
  • Dyke
  • Sill
  • Flow
  • Structure

Cite this

Magee, C., Muirhead, J., Schofield, N., Walker, R. J., Galland, O., Holford, S., ... McCarthy, W. (2019). Structural signatures of igneous sheet intrusion propagation. Journal of Structural Geology, 125, 148-154. https://doi.org/10.1016/j.jsg.2018.07.010