Modelling the heat pulses generated on a fault plane during coseismic slip: Inferences from the pseudotachylites of the Copanello cliffs (Calabria, Italy) A. Caggianelli a, * , S. de Lorenzo b,c , G. Prosser d a Dipartimento Geomineralogico, Universita ` di Bari, Italy b Dipartimento di Geologia e Geofisica, Universita ` di Bari, Italy c Centro Interdipartimentale di Ricerca per la Valutazione e la Mitigazione del Rischio Sismico e Vulcanico, Universita ` di Bari, Italy d Dipartimento di Scienze Geologiche, Universita ` della Basilicata, Potenza, Italy Received 21 July 2004; received in revised form 11 May 2005; accepted 19 May 2005 Available online 1 July 2005 Abstract A pseudotachylite vein network crosscutting late Hercynian foliated tonalites can be observed along the Copanello cliffs (Calabria, Southern Italy). Pseudotachylites formed during the Oligocene–Miocene at intermediate crustal levels (ca. 10 km). They show variable thickness ranging from few mm up to 10 cm, as observed in injection veins branching from the fault plane. Microscopic observations indicate that pseudotachylite matrix mainly consists of plagioclase (An 46 –An 58 ) and biotite microlites. Rounded clasts of quartz, plagioclase or of plagioclase–quartz lithic fragments are disseminated in the matrix. Intergranular, flow and spherulitic textures are commonly observed. Microstructural features are consistent with rapid crystallisation from melt. EDS analyses of rare and tiny glass veins indicated a trachyandesite or An 50 plagioclase melt composition. The conditions for pseudotachylite formation were reproduced by an analytical model taking into account the heat released by friction along a horizontal fault plane during a seismic event. The model is based on a three-stage rupture history that includes nucleation, propagation and stopping. In addition, by means of a numerical approach, the model reproduces cooling that follows the stopping stage. According to previous studies, the thermal perturbation induced by fault displacement is very intense. In fact, temperatures exceeding the tonalite and even An 50 plagioclase liquidus (1470 8C) are reproduced by small amount of slip (V 6 cm) in suprahydrostatic regime. On the other hand, the thermal perturbation is strongly localised and of short duration. Peak temperatures abruptly decrease at a short distance from the fault plane (typically in few millimetres). In these conditions a thin film of melt can be produced. Therefore, the presence of cm-scale pseudotachylite veins can be only explained assuming an efficient and fast melt migration towards dilatant sites, such as pull-apart structures and 0040-1951/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.tecto.2005.05.017 * Corresponding author. E-mail address: caggianelli@geomin.uniba.it (A. Caggianelli). Tectonophysics 405 (2005) 99– 119 www.elsevier.com/locate/tecto