Abstract: Quartz-monzodioritic dykes have intruded the Hercynian continental lower crust of Calabria at 323±5 Ma. Pseudosection and average PT calculations have been performed using THERMOCALC. The obtained P (average PT) and T (pseudosection and average PT) values indicate that the quartzmonzodioritic dykes have intruded the 750 °C hot metapelitic-migmatitic country-rocks at a depth of about 32 km, with a temperature of ca. 850 °C. Microstructural analysis suggests that deformation of the dykes started at hypersolidus conditions during emplacement and continued after cooling at subsolidus granulite facies conditions together with the country rocks. During this deformation event, which started not later than 323±5 Ma ago, the main Sn+1 schistosity evolved. Vorticity analysis of the quartz-metadioritic dykes and of the metapelitic country rocks shows that the Sn+1 schistosity evolved during a general shear deformation characterized by 60 to 70 percent of pure shear. This high percentage of pure shear suggests that the main Sn+1 schistosity evolved in the hot lower crust undergoing extension during vertical shortening. A horizontal attitude of this extensional schistosity is confirmed by retro-deformation of the today obliquely SE-ward dipping Sn+1 schistosity. Extension continued with time and propagated upwards within the crust, affecting the middle crust in a time interval of 306±1 to ca. 300 Ma when huge masses of granitoid rocks intruded it. The deepest batches of these granitoid bodies show a gneissic schistosity which developed under ductile conditions, while granitoids at higher levels became deformed in a brittle fashion. Our whole data set is consistent with a late Hercynian evolution in Calabria characterized by a progressively crust overlying a mantle that gradually rose during lithospheric extension. This extension was asynchronous, starting at 323±5 Ma in the lower crust and affecting higher crustal levels at progressively later times.

A dike network transecting a basement of intrusive and metamorphic rocks related to the Hercynian orogeny is exposed in the Sila Grande (southern Italy). Dike magmatism, similarly to other regions of the western Mediterranean, such as Sardinia, Corsica, and Catalonia, is of calc-alkaline to alkali-calcic affinity. Zircon U-Pb geochronology indicates that dike magmatism took place between 295 +/- 1 to 277 +/- 1 Ma, after the main late Hercynian emplacement of granitoids (306 +/- 1 Ma). Barometry indicates that the basement underwent exhumation of 8 +/- 3 km before dike injection. The dike network has a geometrical arrangement consistent with a transtensional stress regime that resulted in ductile thinning of the lower crust during the late stage of the Hercynian orogeny and concurrent fracturing of the upper crust that made possible magma ascent through dikes. The proposed tectonic evolution is related to dismemberment of the southern Hercynian belt in the central Mediterranean area as a result of dextral transtension of Gondwana in relation to Laurasia during the Pennsylvanian-Early Permian.

Outcrops of the pre-Mesozoic basement, representative of the whole Hercynian continental crust are exposed in Calabria. This is the result of Tertiary geological evolution that brought to the surface different crustal levels. This geological field trip aims to provide a general picture of the continental crust that hopefully may represent a reference frame for geochemical, rheological and geophysical models. The itinerary develops in central and southern parts of Calabria, namely in the Serre massif and in the promontories of Capo Vaticano and Monte Sant’Elia. In three days it is possible to examine compositional and structural features across an entire crust section. Thus rocks affected by very low-grade to granulite facies metamorphism and distinctive features of granitoids emplaced at different structural levels will be examined. The effects of the intense thermal perturbation produced by granitoid emplacement are visible both in the upper and in the lower crust, in a sharp metamorphic aureole and in a migmatitic border zone, respectively. Finally, some cases of Paleozoic rocks with strongly partitioned deformation, produced by Tertiary tectonics in the brittle and the ductile domains, can be observed.

The reconstruction of the tectono-metamorphic evolution of the Variscan intermediate and upper crustal section exposed in the southern Serre Massif (Calabria, southern Italy) is crucial for a broader understanding of the crustal dynamics during the Variscan orogeny. In the southern Serre Massif, Variscan tectonics juxtaposed the Mammola Paragneissic unit (hereafter MPu), representative of the intermediate crust, and the Stilo-Pazzano Phyllite unit (SPu), representative of the upper crust. Subsequently, both units were affected by a contact metamorphic event related to the emplacement of the Upper-Carboniferous Serre batholith. Within the MPu, in the Levadio Stream area, garnet-hornblende bearing metandesitic lenses are locally interlayered with the paragneisses. The juxtaposition of the MPu and SPu is marked by a mylonitic shear zone affecting also the metandesite. This study examines via phase equilibria modelling the metamorphic evolution of a sheared garnet-hornblende bearing metandesite. To this purpose, the rock was modelled in the MnO–Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–O system using the software THERMOCALC v.3.45, with the thermodynamic dataset ds63, including a – x models for both metapelitic and metabasic minerals. The pre-peak metamorphic mineral assemblage (ep-q-pl-mu-chl-bi-rieb) is hosted as primary inclusions in garnets having the following composition: almandine (50-53%) - grossular (29-31%) - spessartine (17-20%). The constructed P-T pseudosection shows that the peak mineral assemblage (g-ep-mu-bi-chl-rieb-ab-sph-q-H2O) was stable in a wide, low-variance P-T field of 6 – 13 kbar and 350 – 525 °C. Garnet isopleth modelling suggests P-T conditions for the regional metamorphic peak of 7.9 – 9.2 kbar and 495 – 510 °C. The subsequent, near isothermal exhumation from about 32 to 10 km depth at 450 – 500 °C brought the metandesite close to the emplacement level of the Serre batolith (at 2.7 kbar). The constructed T-MH2O pseudosection points to T values of 570 – 593 °C for the peak pl-bi-q-g-hb-sph mineral assemblage of the contact metamorphism, under H2O-saturated conditions. The derived P-T path for the garnet-hornblende bearing metandesite is consistent with the one derived by Angì et al. (2010) for the MPu paragneiss, and highlights that comparable peak pressures were reached at the regional metamorphic acme in the southern Serre Massif within the MPu, as well as within the granulite facies rocks cropping out in the north. This suggests that the thermal gradient significantly changed across the Variscan chain exposed in Calabria in response to distinct tectono-magmatic contexts.

The reinterpretation of public seismic profiles in the Adriatic offshore of Gargano (Apulia, southern Italy) allowed the detection of a kilometre-scale salt-anticline, the Tremiti diapir, within the larger Tremiti Structure. This anticline was generated by diapirism of Upper Triassic anhydrites within a thick Mesozoic to Quaternary basinal sedimentary succession. Both internal stratal patterns and shapes of Plio-Quaternary units, and the occurrence of an angular unconformity between early Tortonian and Pliocene rocks on the Tremiti Islands, suggest that halokinesis began during the late Miocene and is still active today. An ancient extensional SE dipping fault, cutting an older Mesozoic low-amplitude anhydritic ridge, played an important role during salt mobilization, which was promoted by NW-SE shortening. The diapir grew in the footwall of this fault, causing its upward propagation. In some places, the ancient fault served as a preferential channel for the upward migration of the anhydrites.

Sinkholes are the main karst landforms characterizing the Salento Peninsula, which is the southernmost part of the Apulia region of southern Italy. They occur both as evolving recent phenomena and old or relict features testifying to ancient phases of karst processes acting in the area. Most of the sinkholes were formed by karst processes that may be reactivated, a risk to the anthropogenic structures nearby. To highlight such a subtle hazard, an area located a few kilometers from Lecce, the main town in Salento, was the subject of geological, morphological, and geophysical investigations. Historical analysis of multi-year aerial photographs, in particular, allowed identification of several phases in the recent evolution of a particular sinkhole, and demonstrated the need to carefully evaluate the likely evolution of similar features in Salento.

The mineralogy of ductilely sheared rocks is controlled by the bulk rock composition of the protolith, together with the P-T conditions of shearing. However, the mineral assemblages of shear zones acting as open system may be strongly influenced by the occurrence of mass transfer processes induced by channeling H2O-rich fluids and mobilizing major elements. Major element mobility is also related to the fluid chemistry, which can be affected by the fluid source location, i.e. the shear zone host-rocks or the shear zone far-field. Recent case studies suggest that significant whole rock compositional changes occurred within ductile shear zones in response to fluid infiltration from the host-rocks, whereas other case studies show that whole rock compositional changes within ductile shear zones occurred due to infiltration of fluids from far-field sources. To investigate the presence of common features regarding the gain and loss of mobilized major elements with respect to the thermobaric conditions of shearing and the fluid source, a review of literature case studies dealing with felsic sheared protoliths has been undertaken. Qualitative results suggest high mobility of major elements under greenschist facies conditions whatever the tectonic context. Under compressive tectonics, qualitative outcomes show that Si has the highest mobility whatever the fluid source location and that sheared felsic rocks are always enriched in Mg relative to Fe. Moreover, a preferential gain of Al and Fe with respect to the fluid source is shown.

New laser ablation inductively coupled plasma mass spectrometry U-Pb dating on zircon and monazite was performed to estimate the time required for the building of the Serre batholith in Calabria. Age spectra from the bottom and top of the pluton are characterized by two main peaks at 306 and 295 Ma, resulting from a mutual interference between serial intrusive events. On this basis, the emplacement of the top granodiorite layer postdates by about 10 m.yr. emplacement of the lower tonalite layer. These results have been incorporated into a two-dimensional numerical thermal model, assuming overaccretion of a batholith in an extensional tectonic regime. With this approach it was possible to reproduce pressure-temperature paths for various levels of the continental crust and define timing for low-pressure regional and contact metamorphism. In a unique tectonomagmatic scenario the model reproduces re- gional low-pressure metamorphic effects in the lower to intermediate continental crust and, with a time lag of about 6 m.yr., contact metamorphism in the upper crust. Finally, we propose a conceptual model for the emplacement of the Serre batholith in an extensional tectonic setting. Space for magma can be created by lower crust thinning and rock uplift at the bottom and top of the batholith, respectively.

Abstract – Tectonic and thermal perturbations, related to emplacement of granodiorite in the upper continental crust, have been investigated in the late-Hercynian basement exposed in southern Calabria (Italy). Here, the structural aureole is marked by the presence of a major rim fold adjacent to the intrusive contact for a length of at least 20 km. Geometrical analysis of the structural aureole and related foliations, lineations and crenulations reveals that the perturbed zone is at least 3000 m wide and characterized by an open synform trending nearly parallel to the intrusive contact. This pattern is compatible with a laccolith-like mode of magma emplacement, related to the accretion of the pluton that shouldered weak phyllitic and slaty wall rocks. The metamorphic aureole, about 1800 m wide, is characterized by biotite, cordierite and andalusite that appear sequentially in spotted schists and hornfelses approaching the intrusive contact. The peak assemblage equilibrated between 535 and 590 ◦C at pressures between 175 and 200 MPa, confirmed by Al-in-hornblende barometry on granodiorite. Microstructural analysis allowed the inference of a time lag between the thermal and tectonic perturbations. With the aid of thermal modelling it was possible to quantify the time required to reach the peak temperature at a distance from the intrusive contact where cordierite spots and andalusite porphyroblasts clearly overprint crenulations. This estimate represents the time limit to accomplish deformation in the inner portion of the aureole and thus indicates a minimum strain rate of 4 × 10−14 s−1 within the country rocks during granodiorite intrusion.

New microstructural data on the mylonites from the well-exposed Palmi shear zone (southern Calabria) are presented with the aim to shed light on both the kinematics and the geometry of the southwestern branch of the Alpine belt during Eocene. In the study area, located between the Sardinia–Corsica block and the Calabria–Peloritani terrane, previous large-scale geodynamic reconstructions suggest the presence of strike–slip or transform fault zones dissecting the southwestern branch of the Alpine belt. However, there are no field data supporting the oc- currence of these structures. This paper uses vorticity analysis technique based on the aspect ratio and the long axis orientation of rigid porphyroclasts in mylonitic marbles and mylonitic granitoids, to estimate the contribution of pure and simple shear of deformation during the movement of the Palmi shear zone. Porphyroclasts aspect ratio and orientation were measured on thin sections using image analysis. Es- timates of the vorticity number, Wm, indicate that the Palmi shear zone recorded general shear with a contribution of pure shear of c. 65%. Then, the Palmi shear zone can be interpreted as a segment of a left-lateral transpressive bend along the southern termination of the Eocene Alpine front.