Coeval compressional deformation and volcanism in the central Andes, case studies from northern Chile (23°S–24°S)

Abstract

In this contribution we examine the relationship between active compression and construction of Pleistocene volcanoes in the present‐day magmatic arc of the central Andes (23°S–24°S). Deformation produced several N–S striking, ∼40 km long subparallel ridges. These ridges formed by folding of Pliocene ignimbrites and upper Pliocene and Pleistocene lavas; they are asymmetrical in profile and have a gentle back limb and steeper frontal limb. Andesitic monogenetic volcanoes show a close spatial relationship with the ridges; some volcanoes are on the hinge zone, whereas others lay on the sides of the ridges. We interpret this spatial pattern as a result of magma storage and migration along a system of subhorizontal reservoirs and reverse faults. Magma reservoirs probably formed along flat portions of reverse faults between ramp structures that serve as episodic magma transport pathways.

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.…”

“…1b), the Cenozoic subvolcanic body of the Cerro Palao Mahuida is placed over the fault trace of an exposed basement-involved backthrust and it was interpreted as emplaced using this fault as a channelway and under a compressive stress field (Dimieri, 1992b). 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).…”

Magma chambers and localization of deformation during thrusting

“…Tibaldi, 2005; Galland et al. , 2007a; Gonzalez et al. , 2009) or in several other places in the world (e.g.…”

“…Volcanic edifices that have developed coevally with and interact with compressional structures, as in the Andean chain (e.g. Tibaldi, 2005;Galland et al, 2007a;Gonzalez et al, 2009) or in several other places in the world (e.g. Tibaldi et al, 2010), may be excellent candidates for testing the above results.…”

“…Tibaldi, 2005, 2008; Galland et al. , 2007a; Gonzalez et al. , 2009 and references therein), the modalities of the interaction between volcanic edifices and contractional structures remain, in part, to be defined.…”