Multiple injections of magmas along a Hercynian mid-crustal shear zone (Sila Massif, Calabria, Italy)

Syn-tectonic late-Hercynian granitoids, emplaced at mid-crustal level through multiple dyke injections, are well-exposed in a ~1 km-long section, in the southern Sila Massif (Calabria, Italy). The fieldwork study permitted us to reconstruct the following order of emplacement: (i) granodiorites with euhedral Kfs megacrystals (Grd1, in the main text) and heterogranular granodiorites with coarse rounded Pl and Kfs in a fine-grained biotite-rich matrix (Grd2); (ii) granodiorites with a nearly homogeneous grain size (Grd3); (iii) tonalite; and (iv) granite. Both in the wall-rock, represented by migmatitic paragneisses, and in the deformed granitoids the foliation attitude is substantially homogeneous, striking about N140 with a dip of 50-60° to the NE. The magmatic lineation is defined by the preferred alignment of euhedral feldspars, parallel to the mineral lineation observed in the host rocks. Micro- and meso-structural analyses indicate that foliation evolved from melt-present to solid-state conditions. Feldspar tiling, S/C structures, ?-type structures, c-axis quartz orientations commonly suggest a top-to-the-west sense of shear during magma injection and deformation under decreasing temperatures. Age of magma emplacement is constrained by U/Pb datings at 304-300 Ma, coeval with the regional metamorphic peak. Foliated granitoids and wall-rock are intruded by poorly foliated Hbl-gabbro and, finally, by undeformed leucogranite, pegmatite and felsic porphyritic dykes. New U/Pb datings of the last intrusion event indicate an age of emplacement of 281 ± 8 Ma, providing a minimum estimate for the end of the shear strain at mid-crustal level. © 2008 Elsevier Ltd. All rights reserved.