Abstract
A revision of late Palaeozoic tectonics recorded in Tuscany, Calabria and Corsica is here presented. We propose that, in Tuscany, upper Carboniferous-Permian shallow-marine to continental sedimentary basins, characterized by unconformities and abrupt changes in sedimentary facies, coal-measures, red fanglomerate deposits and felsic magmatism, may be related with a transtensional setting where upper-crustal splay faults are linked with a mid-crustal shear zone. The remnants of the latter can be found in the deep-well logs of Pontremoli and Larderello-Travale in northern and southern Tuscany respectively. In Calabria (Sila, Serre and Aspromonte), a continuous pre-Mesozoic crustal section is exposed, where the lower-crustal portion mainly includes granulites and migmatitic paragneisses, together with subordinate marbles and metabasites. The mid-crustal section, up to 13 km-thick, includes granitoids, tonalitic to granitic in composition, emplaced between 306 and 295 Ma. They were progressively deformed during retrograde extensional shearing, with a final magmatic activity, between 295 ± 1 and 277 ± 1 Ma, when shallower dykes were emplaced in a transtensional regime. The section is completed by an upper crustal portion, mainly formed by a Palaeozoic sedimentary succession deformed as a low-grade fold and thrust belt, and locally overlaying medium-grade paragneiss units. As a whole, these features are reminiscent of the nappe zone domains of the Sardinia Variscan Orogen. In Corsica, besides the well-known effusive and intrusive Permian magmatism of the “Autochthonous” domain, the Alpine Santa Lucia Nappe exposes a kilometer-scale portion of the Permian lower to mid-crust, exhibiting many similarities to the Ivrea Zone. The distinct Mafic and Granitic complexes characterizing this crustal domain are juxtaposed through an oblique-slip shear zone named Santa Lucia Shear Zone. Structural and petrological data witness the interaction between magmatism, metamorphism and retrograde shearing during Permian, in a temperature range of c. 800–400 °C. We frame the outlined paleotectonic domains within a regional-scale, strain–partitioned, tectonic setting controlled by a first-order transcurrent/transtensional fault network that includes a westernmost fault (Santa Lucia Fault) and an easternmost one (East Tuscan Fault), with intervening crustal domains affected by extensional to transtensional deformation. As a whole, our revision allows new suggestions for a better understanding of the tectonic framework and evolution of the Central Mediterranean during the late Palaeozoic.
Highlights
The distribution of pre-Mesozoic rocks in the Central Mediterranean is uneven (Fig. 1), with the most relevant exposures in the Alps, and only scattered outcrops, or shallow-crustal subsurface occurences known so far, in and around the Italian peninsula (Rau and Tongiorgi 1981; Cassinis et al 2000 2012; Vai 2001; Scisciani and Esestime 2017). 23 Page 2 of 32The Variscan basement and upper Carboniferous-Permian successions are exposed in the Alpine chain, witnessing continental crustal segments of the different Variscan paleotectonic domains, later involved and deformed, at various crustal levels, during the Alpine evolution
Structural studies of the area (Libourel 1988a, b; Caby and Jacob 2000; Zibra 2006; Zibra et al 2010; 2012) document the same lineation trend and kinematics (Fig. 10e) between the two tectono-magmatic crustal domains (Mafic Complex + Diorite-Granite Complex and Granite Complex) which were juxtposed along an oblique-slip shear zone known as Santa Lucia Shear Zone, with magmatism, metamorphism and shearing that interacted over a temperature range from 800 to 400 °C, when deformation was localized along the Bocca di Civenti Shear Zone (Zibra et al 2010, 2012)
After the Mesozoic rifting, the Santa Lucia domain was still attached to the “Autochothonous” (Durand Delga 1984; Rossi et al 2006; Li et al 2015) or part of an Ocean Continent Transition (OCT) or AlKaPeCa-type microblock (Lahondere 1996; Michard et al 1992; Molli and Malavieille 2011; Lin et al 2018), we suggest that a regional-scale transtensional fault, here called Santa Lucia Fault, existed during Permian, east of Corsica-Sardinia
Summary
The distribution of pre-Mesozoic rocks in the Central Mediterranean is uneven (Fig. 1), with the most relevant exposures in the Alps, and only scattered outcrops, or shallow-crustal subsurface occurences known so far, in and around the Italian peninsula (Rau and Tongiorgi 1981; Cassinis et al 2000 2012; Vai 2001; Scisciani and Esestime 2017)
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