Tectonic framework of Uccellina Mounts

Geological mapping and macro and microstructural analyses led to reconstruct the structural setting and the tectonic evolution of Monti dell’Uccellina area (Southern Tuscany). A polyphase tectonic history, characterized by three main tectonic events linked to the development of folds and cleavages has been recognized. During the fi rst tectonic phase east verging F1 folds with axial plane foliation developed under very low grade metamorphic conditions, as highlighted by illite and chlorite cristallinity data. The main stacking of the nappe pile occurred during the fi rst tectonic phase. The further tectonic evolution is characterized by the development of thrusts, associated with East verging shear zones, that led to the emplacement of three tectonic complexes, each one made by the superposition of three different tectonic units that from top to bottom are “Collelungo Unit”, “Vacchereccia Unit” and “Monti dell’Uccellina Unit”. During the second tectonic phase, the nappe pile is deformed by a kilometric scale upright antiform gently plunging toward the North. The last tectonic phase, related to post-collisional extensional tectonics, is characterized by the development of folds and low angle detachment faults. The new data pointed out for the assignment of “Pseudoverrucano” Auctt. formation, recognized by previous Authors in the north-western part of the study area, to the Triassic Verrucano group. The reconstruction of the geological setting of the different tectonic units led to recognize that the Triassic Verrucano formation occurs in two different tectonic units: the Vacchereccia Unit, made up only by a slice of Verrucano, and at the bottom of the Monti dell’Uccellina Unit where it constitutes the base of a post-triassic continental margin sequence

Late Hercynian shear zones in Sardinia

In the past few years two main late Hercynian shear zones have been identified in Sardinia: the Mount Grighini shear zone in the centre of the island and the Posada Valley shear zone in the north. Both are dextral wrench shear zones, affecting the Hercynian basement during the Late Carboniferous, and characterized by a simple shear deformation with an evolution from cataclastic to ultramylonitic rocks. The meso-and microstructural deformation features are discussed here. On the basis of these, two maps of the different deformative zones within the shear zones have been prepared and both displacements have been calculated. An attempt has also been made to correlate with other late Hercynian shear zones in continental Europe on the basis of common features and geological constraints

Late orogenic structures and orogen-parallel compression in the Northern Apennines

The Northern Apennines is an orogenic belt characterized by a northeastward propagation of deformation during the main collisional event. Field mapping, together with structural analyses, pointed to the presence of several later transversal and parallel structures, with respect to the main trend of the chain. These are mainly represented by strike-slip faults and folds. Steeply dipping NW-SE trending folds are related to a continuing NE-SW direction of shortening. One of the most striking transversal faults is the dextral fault located in the northern side of the Apuan Alps, near the boundary with the Tuscan Nappe. It trends nearly ENE-WSW and it develops for about ten kilometers. Other transversal structures are represented by upright folds, recognized in the Tuscan Nappe and in the Massa Unit outcropping in several areas of the Northern Apennines. The direction of shortening related to these structures, both folds and faults, is oriented roughly NW-SE, i.e. parallel to the main trend of the Northern Apennines. This orogen-parallel compression is related to the development of the metamorphic domes. The two directions of horizontal shortening induced buckling and vertical growth in the metamorphic domes, so enhancing the process of exhumation of the metamorphic rocks. The domes are later affected by collapse folds and low- to high-angle normal faults related to extensional tectonics. Our structural data together with the available data on fluid inclusions in syntectonic veins in the Tuscan Nappe indicate a post-D1 decreasing pressure. This suggests that the Tuscan Nappe was exhumed in a compressive tectonic setting starting from the D1 deformation phase up to the later phases

Italian geological mapping in northern Victoria Land: the GIGAMAP project

none3G. CAPPONI; M. MECCHERI; P.C. PERTUSATICapponi, Giovanni; M., Meccheri; P. C., Pertusat

Early Ordovician terrane accretion along the Gondwanian margin of the East Antarctic Craton: new Pb/Pb titanite ages from Tonalite Belt, North Victoria Land, Antarctica,

Early Palaeozoic subduction of the palaeo-Pacific plate and terrane accretion along the palaeomargin of the East Antarctic Craton is well-documented in North Victoria Land, where the Tonalite Belt is a complex of synkinematic intrusions emplaced within the Lanterman–Murchison Shear Zone at the boundary between the Wilson Terrane and the allochthonous Bowers Terrane. Stepwise leaching Pb/Pb and U–Pb studies of titanite separates carried out on two well-foliated samples of tonalites yielded ages of deformation bracketed between 490 and 480 Ma with an isochron age of 480 ±13 Myr. Ar/Ar and K–Ar ages of 477 Myr in the metamorphic rocks of accreted terranes point to fast cooling and uplift after accretion. The new titanite ages, compared with a regional distribution of magmatic and metamorphic ages, indicate an early Ordovician age for terrane collision and amalgamation. As a consequence of collision, subduction shifted to an outward position along the palaeomargin of the East Antarctic Craton

Tectonic history of the Monti dell'Uccellina range, southern Tuscany, Italy

Geological mapping, combined with macroscopic and microscopic structural analyses have been used to unravel the geometry and tectonic evolution of the Monti dell'Uccellina group (Southern Tuscany). A polyphase tectonic history has been recognized, characterized by three main tectonic events associated with the development of shear zones, folds and foliations. During the first tectonic phase, East verging F1 folds with axial plane foliation developed under very low-grade metamorphic conditions, as highlighted by illite crystallinity data and by the calcite-dolomite geotnermometer. Several piled tectonic units, belonging to the Tuscan and Subligurian domains, constitute the backbone of the Monti dell'Uccellina range. These are, from bottom to top: 1) the Torre Cannelle Unit, made up by the Verrucano Group rocks; 2) the Talamone Unit, made up by the Calcare Cavernoso Formation; 3) the Monti dell'Uccellina Unit, represented by a passive margin sequence spanning from the Triassic Verrucano group at the base to the Tertiary Scaglia Fm. at the top; 4) the Vacchereccia Unit, represented only by Triassic Verrucano Group; 5) the Collelungo Unit, made up by the Calcare Nummulitico Fm. followed by the Macigno Fm; 6) the Canetolo Unit (Sub-Ligurian Unit Auctt.) represented by the «Argille & Calcari» Fm. Stacking of the nappe pile occurred during the first tectonic phase (Dl) in two stages: during the first stage the main tectonic units were emplaced. The second tectonic stage is characterized by later thrusts that cut through the older ones, all of them with a topto-the- East sense of movement, that led to the emplacement of three tectonic complexes. Each complex comprises three superposed tectonic units that are from top to bottom the Collelungo Unit, the Vacchereccia Unit and the Monti dell'Uccellina Unit. During the second tectonic phase (D2), the nappe pile was deformed by a kilometre-scale N-S trending upright antiform gently plunging towards the North. The last tectonic phase is characterized by the development of sub-horizontal folds and of low-angle detachment faults that were produced during the post-collisional extensional events. A detailed survey, that was achieved through compilation of a 1:10.000 scale map, has clarified the structural and stratigraphie position of the «Pseudoverrucano» Auctt. Formation, whose attribution has been debated for a long time. According to our data it can be referred to two different tectonic units: the Vacchereccia Unit, represented only by this formation, and the Monti dell'Uccellina Unit where it constitutes the bottom of a post-Triassic continental margin sequence