Dyke propagation and sill formation in a compressive tectonic environment

Abstract

[1] 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.

Igneous sills record far-field and near-field stress interactions during volcano construction: Isle of Mull, Scotland

“…Numerical and scaled analogue models suggest that when a homogeneous host is subjected to a remote horizontal compressive stress, rotation of a feeder dyke may occur over several hundreds of metres to kilometres (Menand et al, 2010;Maccaferri et al, 2011). It is not clear from our field observations whether the LSSC is fed by sills, or by dykes, and the vertical limitation in exposure may preclude this observation.…”

Strengths and strain energies of volcanic edifices: implications for eruptions, collapse calderas, and landslides

“…Some papers explicitly deal with the effects of overpressure-related variation in dike aperture and external loading on magma flow during eruptions (Costa et al, 2009(Costa et al, , 2011. Other recent papers on this and related topics include Canon-Tapia et al (2006), Menand et al (2010), Geshi et al (2010Geshi et al ( , 2012, Taisne et al (2011), and Maccaferri et al (2010, 2011. A detailed statistical summary of "failed eruptions" (mostly arrested dikes) is provided by Moran et al (2011).…”

“…Below, we will briefly consider a spherical chamber. However, sill-like chambers are presumably the most common in the world, and are the geometries often inferred from seismic and other geophysical measurements for active chambers, as well as for many fossil chambers, or plutons (Gudmundsson, 1990;Annen and Sparks, 2002;Gudmundsson, 2006;Kavanagh et al, 2006;Menand et al, 2010;Menand, 2011). Thus, the focus is on sill-like magma chambers.…”

Stress Controls of Monogenetic Volcanism: A Review

“…In such cases, any stress barrier caused by a density or rheological contrast, presence of a tectonic structure, or existence of a differential stresses may induce stress rotation and make the sheet intrusion divert from the direction it was propagating, or even to arrest it in case the overpressure required to surpass that obstacle is not achieved. This may explain how dykes may divert into sills forming new magma reservoirs (Menand et al, 2010;Gudmundsson, 2011a), or how dykes or sills may propagate for tens of kilometers inside the crust before becoming vertical again and erupting at surface (e.g., Martí et al, 2013) or stopping before it reaches it (e.g., Wright et al, 2006;Ayele et al, 2007). Figure 5.…”

“…In the literature there are excellent experimental and theoretical approaches on magma transport and on the mechanics and fluid-dynamics of magma-filled cracks (e.g., Pollard, 1969Pollard, , 1973Pollard and Muller, 1976;Pollard, 1981, 1982;Delaney et al, 1986;Pollard and Segall, 1987;Takada, 1989;Gudmundsson, 1990Gudmundsson, , 2011aLister and Kerr, 1991;Rubin, 1993a,b;Rubin, 1995;Dahm, 2000;Muller et al, 2001;Roman and Heron, 2007;Menand, 2008Menand, , 2011Taisne and Jaupart, 2009;Maccaferri et al, 2010Maccaferri et al, , 2011Menand et al, 2010;Taisne et al, 2011;Gudmundsson, 2012;Le Corvec et al, 2013c;Rivalta et al, 2015), as well as on rock stress (e.g., Zang and Stephansson, 2010), and we address the reader to these contributions. In this section we only provide a basic background necessary to follow the rest of this review.…”