Dyke propagation and sill formation in a compressive tectonic environment

Menand, T. and Daniels, K. A. and Benghiat, P. (2010) Dyke propagation and sill formation in a compressive tectonic environment. Journal of Geophysical Research: Solid Earth, 115 (B8). ISSN 2156-2202 DOI https://doi.org/10.1029/2009JB006791

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Sills could potentially form as a result of dykes modifying their trajectory in response to remote tectonic compression. Here, we use analogue experiments to investigate how a buoyant vertical dyke adjusts its trajectory to a compressive remote stress to form a sill, and over which vertical distance this sill formation does occur. Our investigation is restricted to an intrusion propagating through a homogeneous solid, which enables us to identify the characteristic length-scale over which a dyke responds to remote stress compression, independently of the presence of crustal layers. The experiments involve the injection of air in a gelatine solid that experiences lateral deviatoric compression. The response of the buoyant air crack to the compressive stress in not instantaneous but operates over some distance. An important observation is that some cracks reach the surface despite the compressive environment. Dyke-to-sill rotation occurs only for large compressive stress or small effective buoyancy. Dimensional analysis shows that the length-scale over which this rotation takes place increases exponentially with the ratio of crack effective buoyancy to horizontal compressive stress. Up-scaled to geological conditions, our analysis indicates that a dyke-to-sill transition in response to tectonic compression in homogeneous rocks cannot occur over less than two hundred meters and would need several kilometers in most cases. This is typically greater than the average thickness of lithological units, which supports the idea that crustal heterogeneities play an important role in determining the fate of dykes and in controlling where sills could form.

Item Type: Article
Uncontrolled Keywords: NIL AREP
Subjects: 02 - Geodynamics, Geophysics and Tectonics
Divisions: 02 - Geodynamics, Geophysics and Tectonics
Journal or Publication Title: Journal of Geophysical Research: Solid Earth
Volume: 115
Identification Number: https://doi.org/10.1029/2009JB006791
Depositing User: Sarah Humbert
Date Deposited: 30 Aug 2013 18:07
Last Modified: 30 Aug 2013 18:07
URI: http://eprints.esc.cam.ac.uk/id/eprint/2867

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