Igneous sheet intrusions are segmented across several orders of magnitude, with segment tip geometry commonly considered indicative of the propagation mechanism (brittle or non-brittle). Proposed propagation mechanisms are inferred to represent host rock mechanical properties during initial magma emplacement; typically, these models do not account for segment sets that show a range of tip geometries within the same lithology. We present a detailed structural characterization of basaltic sill segments and their associated host rock deformation from the Little Minch Sill Complex, Isle of Skye, UK, and a broader comparison with segment geometries in three additional intrusive suites (Utah, USA; and Mull and Orkney, UK). Each separate host lithology shows multiple tip geometries and styles of host rock deformation, from elastic-brittle fracture, to viscous indentation and fluidisation. We attribute this range of host rock deformations to evolving conditions that occur at the tips both during sheet growth and arrest.
This work was undertaken during T.L. Stephens’s PhDstudentship at the University of Leicester, supported bythe Central England Natural Environmental ResearchCouncil (NERC) Training Alliance (CENTA) (award ref-erence: 1503848). The authors would like to thankMitch Miller for assisting with fieldwork. Thanks arealso extended to SteffiBurchardt and Richard Englandfor their constructive comments on an earlier versionof the manuscript, which led to significant improvements. We would also like to thank the Volcanica ed-itor Pete Rowley, along with Sam Thiele and an anonymous reviewer for their constructive reviews, and SamPoppe for kindly providing comments on the pre-printmanuscript, all of which led to an improved final version.
Data Availability StatementThe data used for this study is available in the supple-mentary files alongside the online version of this article.
- Sill segment geometry
- sill emplacement mechanism
- structural mechanisation