ALBERT

Description: Biostratigraphy based on calcareous nannofossils, integrated by magnetostratigraphic, geochronological and isotopic data, allowed establishing a precise chronological framework for the Pleistocene succession within the south-western sector of the Crotone Basin (Calabria, Southern Italy), where the Pliocenee Pleistocene global stratotype section and point is defined, thus demonstrating that sedimentation was quasi-continuous during most of the Lower and Middle Pleistocene. At a large scale, the Pleistocene succession in this sector of the Crotone Basin is characterized by an evident shallowing-upwards trend, showing facies changes from bathyal to shelfal to littoral/continental. However, comparison between adjacent sectors within the investigated area demonstrates that stratigraphic architectures change vastly on very short distances. Our chronological constraints indicate that such changes in sedimentation styles probably occurred in response to differential subsidence rates, which originated tectonically-controlled synsedimentary structures where accommodation space and sediment yield were allotted unevenly. This articulated physiography led to striking differences in the overall thicknesses and organization of Pleistocene stratigraphies and, eventually, to a distinct diachroneity in the first appearance of shallow-marine deposits. In addition, superimposed are complex interplays between regional and local tectonics, eustasy and orbitally-forced climate changes. These interactions have been highlighted by the oxygen isotope stratigraphy established for a part of the studied succession, which is likely to document almost continuously the interval from Marine Isotope Stage (MIS) 26 to MIS 17. In its younger part (post-MIS 17), chronological ties are poor, as the succession is dominated by shallow-water to continental deposits showing a prominent organization into cyclothems. Nevertheless, based on the chronology of the underlying units, it is feasible that basin infill ended during MIS 15-MIS 14 times.

Description: Published

Description: 1185-1200

Description: 2.2. Laboratorio di paleomagnetismo

Description: JCR Journal

Description: restricted

Description: Hercynian basement rocks and Mesozoic ophiolites of the Calabria-Peloritani terrane drifted in the present position during the opening of western Mediterranean basins (namely Liguro-Provençal and Tyrrhenian basins) since the Oligocene. Basement rocks were partly involved by Alpine (late Cretaceous—Eocene) deformation and metamorphism before the onset of the drifting process. Even though the kinematics of the Alpine deformation in Calabria has been already defined, restoration of structural and kinematic data to the original position and orientation before the opening of the western Mediterranean has never been performed. In this work we present new structural and petrological data on a major tectonic contact of Alpine age exposed in central Calabria (Serre Massif). Structural and kinematic data are then restored at the original orientation in the early Oligocene time, to allow a correct tectonic interpretation. In the Serre Massif the Hercynian basement is sliced into three nappes emplaced during the Alpine orogeny. The upper nappe is formed by a nearly continuous section of the Hercynian crust, consisting of medium- to high-grade metamorphic rocks in the lower portion. The intermediate nappe mainly consists of orthogneisses, whereas the lower nappe is chiefly composed of phyllites. The contacts between the Alpine nappes are outlined by well developed mylonitic and cataclastic rocks. The Curinga-Girifalco Line is a well exposed shear zone that overprints mainly metapelitic rocks of the upper nappe and granitoid orthogneisses of the intermediate nappe. Mylonites of the intermediate nappe typically show overgrowths on garnet and hornblende with grossular-rich and tschermakitic composition, respectively. The Alpine mineral assemblage indicates that deformation took place in epidote-amphibolite facies at pressures ranging from 0.75 to 0.9 GPa. In the investigated area mylonites strike roughly WNW–ESE, with shallow dips towards SSW. Kinematic indicators in mylonites are mostly consistent with a top-to-the-SE shear sense in the present geographic coordinates. The mylonitic belt is affected by later extensional faults outlined by South-dipping cataclasite horizons. Published geochronological data indicate that mylonites and cataclasites developed in Eocene and early Miocene times, respectively. Considering rotational parameters coming from paleomagnetic studies and large-scale palinspastic reconstructions, the shear sense of the Curinga-Girifalco Line has been restored to the early Oligocene position and orientation. Through restoration a top-to-the-S shear sense is obtained. This result is in striking agreement with the convergence direction between Africa and W-Europe/Iberia during Eocene, computed from the North Atlantic magnetic anomalies. Our geodynamic reconstruction, combined with structural and petrological evidence, allows to relate the Curinga-Girifalco mylonites to a thrust related to the southeastern front of the double-verging Alpine chain. The adopted method could be used also for other exotic terranes, such as the Kabylie or the Corsica-Sardinia, to better constrain geometry and evolution of the southern Alpine belt.

Description: A pseudotachylyte vein enclosed in tilted Hercynian lower crust of the Calabrian Serre Massif provides information on the source of a fossil seismic event. The pseudotachylyte contains euhedral garnet that formed by direct crystallization from a frictional melt and not during a later metamorphic overprint. Pseudotachylyte formation started with grain-size reduction caused by ductile deformation and brittle deformation. Subsequent frictional melting affected almost all phases including quartz but excluding monazite. After rapid cooling, chilled margins composed of glass and iron sulphide droplets formed. The central part of the vein solidified as biotite, and plagioclase crystallized directly from the frictional melt. Garnet occurs in three different grain-size classes; there are significant differences between very small garnets in the chilled margins and larger garnets in the central part of the pseudotachylyte vein. This proves that garnet rapidly crystallized from the pseudotachylyte melt after the seismic event. Garnet composition is used to define the depth of garnet growth, implying that the seismogenic zone was located at a depth of about 21–23 km. The melt temperature was between approximately 1515 and 2040 °C, representing the melting points of ß-quartz and monazite, respectively.This study supports the interpretation from seismic data that lower-crustal seismicity occurs and affirms, by direct observation, that the classical jelly sandwich model of the lithosphere is not always appropriate for crustal sections. In contrast to well-known regions with dry and very strong lower crusts (e.g. the Caledonides), the studied part of the Hercynian lower crust contains significant amounts of biotite, which release aqueous fluids during frictional melting. In addition, fluid inclusions in quartz fragments within the pseudotachylyte indicate that fluids probably played an important role during fault-zone evolution at the time of frictional melting.

Description: Slip along low-angle normal faults is a mechanical paradox requiring activation of strain weakening mechanisms. Microstructures present in the slip zones of incipient low-angle normal faults cutting carbonates in the Southern Apennines of Italy show that slip was promoted by two weakening mechanisms producing a reduction of the friction coefficient: (1) high pore fluid pressures; (2) dynamic weakening related to thermal decomposition indicated by decarbonation microstructures and concomitant localized dynamic calcite recrystallization. Furthermore, as a consequence of thermal decomposition, nanoparticles occur as infilling of injection veins, suggesting that powder lubrication processes are active along the slip surface during seismic slip. Supplementary materials: A geological sketch of the study area, detailed field photographs of the studied faults and detailed micrographs are available at http://www.geolsoc.org.uk/SUP18806 .

Description: The Gorgoglione Formation represents the infill of a thrust-top basin, which records the tectonic evolution of the southern Apennines (Italy) since Upper Miocene times. The Upper Miocene basin was divided into two main sub-basins, showing both about NNW-SSW elongation. During ongoing contractional deformation, the Gorgoglione basin was incorporated into the allochthonous units of the Apennine fold-and-thrust belt, as outlined by the emplacement of thrust sheets of internal provenance (Sicilide Unit) and by the development of two main generations of tight to open folds. In this work, the modalities of deformation associated to the incorporation of the Gorgoglione Formation into the fold-and-thrust belt has been documented by means of mineralogical and structural analyses. Mineralogical data show that, in the northeastern sub-basin of the Gorgoglione Formation, the illite content and the order of illite/smectite mixed layer increase near the contact with the overlaying Sicilide Unit. These data are hence used to estimate the relative tectonic load produced by thrusting of the aforementioned tectonic unit. Structural data are consistent with tight, NNW-trending, meso-scale folds particularly frequent in the upper pelitic/arenaceous portion of the Gorgoglione Formation. Within these folded pelitic levels, a well-developed axial-plane foliation, and an ordered I/S (R1 and R3) with higher illite content, is documented. Instead, other folds developed far away from the Sicilide klippen show an incipient axial-plane foliation and a random I/S (R0) with lower illite amount is found in pelites. The data suggest that the eastern sub-basin of the Gorgoglione Formation underwent variable tectonic load, increasing from E to W, as well as deformation produced by thrusting of Sicilide sheet. The mineralogical data also indicate that illitization process is favoured for the high availability of potassium due to the dissolution of k-feldspar. High potassium availability affects the samples subjected to the highest diagenetic degree, characterized by kaolinite illitization process.

Description: In thrust belts, low-angle tectonic contacts are common, and are associated with the stacking of tectonic units and the resulting regional shortening. The Southern Apennines of Italy, where basin and platform sediments are stacked along low-angle regional thrusts caused by the shortening of the Adria passive margin, are no exception. We studied a portion of a north–south-trending, low-angle regional thrust that separates Apennine platform sediments from Lagonegro basin rocks. To the east of the thrust, klippen composed of platform sediments overlying Lagonegro rocks along a low-angle tectonic contact are present. The klippen were first interpreted as remnants of the regional thrust. We performed a detailed structural analysis of the regional thrust, and we examined the structural setting of the klippen. Field evidence and analysis of map patterns revealed that emplacement of low-angle, foreland-propagating thrusts was followed by extensional deformation accommodated by regional east-dipping, low-angle normal faults. At the base of the klippen, we identified low-angle tectonic contacts with an extensional kinematics. We conclude that the klippen were the result of movements of platform sediments and Lagonegro rocks along low-angle normal faults, and not thrusts as previously interpreted. These faults are cut by more recent, high-angle normal faults associated with the opening of the Agri basin. Collectively, we show that evidence of changes in the tectonostratigraphic architecture, fault geometry and kinematics, and fabrics in the thrusts can reveal the presence of low-angle normal faults, the result of an extensional regime. We expect that our findings will contribute to the understanding of the deformation history of part of the Southern Apennines, and of other mountain belts. The results are also important to understand the transition from compression to extension in the Southern Apennines and in similar orogenic belts.

Description: 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 x 10 –14 s –1 within the country rocks during granodiorite intrusion.