Rise and emplacement of magma during horizontal shortening of the brittle crust: Insights from experimental modeling

Abstract

[1] Magmatic activity tends to concentrate at plate margins. At divergent margins, extensional tectonics provide steep conduits for magma to reach the surface. At rapidly convergent margins, such as the Andes, one might imagine that horizontal compression prevents the rise of magma. Nevertheless, volcanoes are also common. In order to study the mechanisms by which magma rises in a compressional context, we resorted to laboratory experiments, in which a brittle crust was shortened, while magma was intruding. Our model materials were (1) cohesive fine-grained silica powder, representing brittle crust, and (2) molten low-viscosity vegetable oil, representing magma. In general, horizontal shortening and injection were coeval but independent processes. Thrust faults accommodated the shortening, while overpressured oil formed hydraulic fractures. In those experiments where there was no shortening, injection resulted in a saucer-shaped intrusive body. In the other experiments, where there was shortening, oil formed a basal sill, before rising along thrust faults. Once in place, the sill lubricated the base of the model, so that arcuate thrusts formed at the leading edge of a plateau. Uplift of the plateau promoted further intrusion of oil at depth. In general, the pattern of deformation and intrusion depended on the kinematic ratio R between rates of shortening and injection. The lengths of the basal sill and plateau increased with decreasing R. On the basis of these results, we have reexamined two natural examples of magmatic complexes, which were emplaced in compressional tectonic settings, Tromen volcano in Argentina and the Boulder Batholith of Montana.

Laboratory Modelling of Volcano Plumbing Systems: A Review

“…• it percolates very little into a very fine-grained granular host medium; • at the end of the experiments, it solidifies after 15-30 min such that (i) the intrusions can be excavated and their shapes analysed in 3D (Galland et al 2009;Galland 2012), or (ii) the models can be cut to reveal how intrusions relate to surrounding structures and overlying surface morphology (Galland et al 2003(Galland et al , 2007a(Galland et al , 2008.…”

Dilatant normal faulting in jointed cohesive rocks: a physical model study

“…However, the influence of pre-existing cohesionless joints on the formation of faults and fractures is largely untested, although this may have great influence on the fault's geometry and evolution (e.g., Butler, 1989;Giambiagi et al, 2003;McGill and Stromquist, 1979;Schultz-Ela and Walsh, 2002;Virgo et al, 2014). This is also of interest for understanding fluid flow through fault zones for naturally fractured reservoirs (Galland et al, 2006(Galland et al, , 2007Le Corvec et al, 2013).…”

Cenozoic structural evolution of the Argentinean Andes at 34º40’S: A close relationship between thick and thin-skinned deformation

“…This feedback between faulting and magmatism is also supported by field evidences in regions where melt-enhanced deformation is an important mechanism (Hollister and Crawford, 1986). Magma can be stored as subhorizontal sills migrating horizontally large distances, in the order of kilometers, along flat segments of thrusts and it may be extruded through ramps (Galland et al, 2007a(Galland et al, , 2007bGonzález et al, 2009). These mechanisms provide an explanation to the foreland expansion of the Huincán subvolcanic rocks considering a lateral migration of the magma along the flat portion of an incipient Carrizalito thrust and subsequent rising through the backthrusts formed in the hangingwall of this structure (Fig.…”

“…More recently, many examples of Neogene-Quaternary magmatism developed under compressional tectonic settings and commonly on top of thick-skinned structures were documented along the Andes (Tibaldi, 2005;Galland et al, 2007a;González et al, 2009). Experimental modelling, performed in order to envisage the interaction of magmatism and tectonics in the Andes, that depicts simultaneous magmatic injection and shortening into a deforming brittle crust, show that the magma forms a basal sill and then typically rises along a thrust fault whereas if the injection outlast shortening the magma rises along backthrusts (Galland et al, 2007b). In these experiments thrust faults provided conduits for fluid so reaching the surface and once in place, the fluid and the soft basal sill act as detachments controlling the pattern of subsequent deformation (Galland et al, 2007b).…”

“…Experimental modelling, performed in order to envisage the interaction of magmatism and tectonics in the Andes, that depicts simultaneous magmatic injection and shortening into a deforming brittle crust, show that the magma forms a basal sill and then typically rises along a thrust fault whereas if the injection outlast shortening the magma rises along backthrusts (Galland et al, 2007b). In these experiments thrust faults provided conduits for fluid so reaching the surface and once in place, the fluid and the soft basal sill act as detachments controlling the pattern of subsequent deformation (Galland et al, 2007b). This feedback between faulting and magmatism is also supported by field evidences in regions where melt-enhanced deformation is an important mechanism (Hollister and Crawford, 1986).…”