Magma emplacement in a thrust ramp anticline: The Gavorrano Granite (northern Apennines, Italy)

Abstract

[1] Magma emplacement in the upper crust is often associated with crustal extension, whereby space for intrusions is made by dilation along transtensive and strike-slip faults. The lenticular shape of several intrusions indicates that a further mechanism for magma intrusion is laccolith emplacement with roof uplift of the overburden. Additionally, melts exploit rheological discontinuities (e.g., sedimentary layering) during their ascent. We present an emplacement model for intrusion of the shallow level Gavorrano Granite (northern Apennine, Italy), which is located at the core of an open anticline. The shape of the intrusion and structural features of the host rocks are indicative of a synkinematic emplacement in a growing thrust anticline. Space was provided by the opening of dilatation zones at the core of anticline as a consequence of different amounts of translation between hanging wall and footwall units which were separated by evaporitic rocks. These evaporitic units acted as major décollement layers. Analog models provide results in good agreement with the structural setting of the anticline and emphasize the possibility that melts filled the dilatation zone, with the décollement layers further facilitating intrusion.

Laboratory Modelling of Volcano Plumbing Systems: A Review

“…23b) (Román-Berdiel et al 1997;Román-Berdiel 1999;Corti et al 2005;Holohan et al 2008b), transpression (Benn et al 1998(Benn et al , 2000, to pure compression (Fig. 23c, d) (Musumeci et al 2005;Mazzarini et al 2010;Montanari et al 2010a, b). All these models produced two fundamental findings: (i) the shapes of magma intrusions are controlled by the deformation, and (ii) vice versa the development of the deformation patterns is perturbed by the presence of a viscous heterogeneity.…”

“…Failure of cohesion-less dry sand occurs according to a Mohr-Coulomb criterion that is defined, in theory, only by the angle of internal friction (ϕ). Dry sand is most applicable for simulating: (i) relatively low cohesion host materials in nature, such as unconsolidated or weakly lithified sediments or tuffs, and/or (ii) large-scale (several to 100s of km) processes involving regional-tectonic deformation (Corti et al , 2003Musumeci et al 2005;Mazzarini et al 2010;Montanari et al 2010a, b), whereby the material strength is assumed to decrease relative to the increasing length-scale (Schultz 1996). Grout (1945) Note that although dry sand is very weak, it does not exhibit a purely or ideally plastic behaviour.…”

Neogene deformation and granite emplacement in the metamorphic units of northern Apennines (Italy): Insights from mylonitic marbles in the Porto Azzurro pluton contact aureole (Elba Island)

“…In the southern side of the Larderello geothermal fi eld, the Gavorrano antiform and the Perrolla syncline give further lines of evidence of early Pliocene shortening . In particular, the Gavorrano antiform is a NS-striking, large-scale thrust ramp fold exploited by the synkinematic emplacement of the early Pliocene Gavorrano granite at its core (Musumeci et al, 2005). The emplacement of early Pliocene igneous bodies during the antiformal growth testifi es to close spatial and temporal relationships between thrusting and magma emplacement at shallow crustal levels with the core of anticlines representing preferential sites for magma emplacement.…”

“…In this suggestion, the Porto Azzurro pluton might be regarded as a passive intrusion exploiting the active thrust system at a shallow crustal level. Synkinematic emplacement of intrusive rocks in active thrust systems is widely documented (Schmidt et al, 1990;Kalakay et al, 2001), and fi eld examples and analog models (Musumeci et al, 2005;Galland et al, 2007;Montanari et al, 2010;Mazzarini et al, 2010b) emphasize the role of rheological anisotropies (i.e., lithologic boundaries and weak décollement layers) and pull-apart zones along thrust sheets or at the top of frontal thrust ramps. The former control the site of magma emplacement, and the latter create space for melt infi lling (Schmidt et al, 1990;Kalakay et al, 2001).…”

Interactions between low-angle normal faults and plutonism in the upper crust: Insights from the island of Elba, Italy: Comment

“…In the Northern Apennines-northern Tyrrhenian Sea orogenic system, large amounts of magma were emplaced at shallow crustal levels from the middle-late Miocene to Holocene (e.g., Serri et al, 1993;Rosenbaum et al, 2008). In this sector of the Apennine chain, the mutual relationships between magmatism and tectonics are still a matter of debate (e.g., Rossetti et al, 1999;Acocella and Rossetti, 2002;Musumeci et al, 2005Musumeci et al, , 2008Rosenbaum et al, 2008). Elba Island, located in the Tyrrhenian Sea ~30 km west of the inner portion of the chain, is a key area where tectonic-magmatic relationships can be studied.…”