Relations between deformation and upper crustal magma emplacement in laboratory physical models F. Mazzarini a, ⁎, G. Musumeci b , D. Montanari c , G. Corti d a Istituto Nazionale di Geofisica e Vulcanologia, Via della Faggiola 32, 56126 Pisa, Italy b Dipartimento di Scienze della Terra, Università di Pisa, Via S. Maria 54, 56126, Pisa, Italy c Centro di Eccellenza per la Geotermia di Larderello, Via G. Carducci, 4, 56044, Larderello (PI), Italy d Istituto di Geoscienze e Georisorse, CNR, Via G. la Pira 4, 50121 Firenze, Italy abstract article info Article history: Received 19 January 2009 Received in revised form 10 June 2009 Accepted 15 September 2009 Available online xxxx Keywords: Mechanical layering of upper crust Magma emplacement Analogue modelling This paper presents analogue models for the emplacement of granitic magmas in upper crustal levels with different mechanical layering during shortening, extension and strike–slip deformation. In particular, we investigated how a weak layer embedded in the upper brittle crust can control the level of magma em- placement. The adopted experimental setup was used to examine the control of soft rocks on the movement of magma through a deforming brittle crust. Model results indicate that the occurrence of a weak (soft) layer embedded in brittle (stiff) material has an impact on the level of magma emplacement. The level of emplace- ment during both extension and shortening was systematically deeper for models with a soft layer than for purely brittle models. During strike–slip deformation the magma pierced the surface in both purely brittle and brittle–ductile models. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Magmatism occurs in different geodynamic settings, producing magmas that are emplaced within the crust at levels that may vary from the middle–lower crust to the surface (volcanism). In the conti- nental crust, magma emplacement is well documented and modelled for crustal shortening (Hutton, 1997; Kalakay et al., 2001; Musumeci et al., 2005; Tibaldi, 2005; Galland et al., 2007a,b; Mazzarini et al., 2008), crustal extension (Roma'n-Berdiel, 1999; Corti et al., 2003) and wrenching (e.g. D'Lemos et al., 1992; Hutton and Reavy, 1992; Brown, 1994; Vigneresse, 1995; Roma´n-Berdiel et al., 1997; Salvini et al., 1997; Rosenberg, 2004; Corti et al., 2005). These examples document the even occurrence of intrusions (at depth in the crust) and volcanoes (at the surface) in quite different tectonic settings (convergent, diver- gent and strike–slip), suggesting that the crustal stress regime does not exert a first order control on the emplacement level of magma within the crust, whereas local strain distribution and near-field stress could provide room for magma emplacement. It is more likely that the level of magma emplacement is controlled by the magma supply rate and crustal rheology at least for continuous magma supply (e.g. Petford et al., 2000). This is particularly evident in the middle and upper crust, where crustal heterogeneities such as lithological and rheological variations lead to mechanical weaknesses, which largely determine the depth of magma emplacement (e.g. Roma'n- Berdiel et al., 1995, 1997; Kavanagh et al., 2006). The role of mechanical weaknesses seems to be more important in the upper crust, where the formation of sills often occurs by magma inflation and roof uplift, exploiting lithological variations. This is testified by the occurrence of several intrusive bodies at shallow depths within brittle–ductile rheolog- ical systems such as sedimentary covers, which contain strength aniso- tropies that stop the ascent of granitic magmas, allowing them to spread horizontally (Roma'n-Berdiel et al., 1995, 1997; Kavanagh et al., 2006) as well as for basaltic magmas (Pasquarè and Tibaldi, 2007; Tibaldi et al., 2008; Tibaldi and Pasquarè, 2008). The above-documented close spatial relationship between the mechanical layering of the crust and the level of magma emplacement is such that the mechanism which allows the migration of magma through a layered crust deserves further investigation. We therefore investigated the role of mechanical discontinuities in the upper brittle crust during the emplacement of magma in compressive, extensional and strike–slip regimes. To this end, analogue experiments were per- formed to simulate magma emplacement within a deforming brittle crust with and without a soft layer. The experimental apparatus as well as the crust and magma analogues are subsequently described. Lastly, the results of the analogue experiment are discussed, focussing on the level of emplacement and on the observed relationships be- tween the simulated intrusions and the structures formed in the simulated deformed brittle crust. Tectonophysics xxx (2009) xxx–xxx ⁎ Corresponding author. Tel.: +39 0508311956; fax +39 0508311942. E-mail address: mazzarini@pi.ingv.it (F. Mazzarini). TECTO-124741; No of Pages 8 0040-1951/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.tecto.2009.09.013 Contents lists available at ScienceDirect Tectonophysics journal homepage: www.elsevier.com/locate/tecto ARTICLE IN PRESS Please cite this article as: Mazzarini, F., et al., Relations between deformation and upper crustal magma emplacement in laboratory physical models, Tectonophysics (2009), doi:10.1016/j.tecto.2009.09.013