Salvatore Laurita

Geochronological study of zircons from continental crust rocks in the Frido Unit (southern Apennines)

Zircon crystals have been separated from gneisses and metagranitoids of the Pollino area (southern Apennines) in order to unravel the origin of these crustal slices within the ophiolite-bearing Frido Unit. The morphology of the zircon has been investigated by SEM, and the internal structure was revealed by cathodoluminescence. Data obtained by U/Pb dating have been used to deduce the age and significance of the different crystallization stages of zircon, connected to the evolutionary stages of the continental crust (Late Paleozoic–Early Mesozoic). Zircons in gneisses are characterized by inherited cores of magmatic origin, bordered by metamorphic rims. Inherited zircons generally show Paleoproterozoic to Ordovician ages, indicating the provenance of the sedimentary protolith from different sources. The exclusive presence of Late Neoproterozoic zircon cores in leucocratic gneisses may suggest a different magmatic source possibly connected to Pan-African events. Late Carboniferous–Early Permian ages are found mainly in zircon rims of metamorphic origin. These are similar to the emplacement ages of protolith of the metagranites in the middle crust portion. Late Carboniferous–Early Permian metamorphism and magmatism testify the extensional collapse of the Hercynian belt, recorded in European, particularly, in the Corsica–Sardinia block and in Calabria. Late Permian–Triassic ages have been detected in zircon rims from gneisses and metagranitoids. These younger ages appear related to deformation and emplacement of albite–quartz veins in both lithologies, and are related to an extensional episode predating the Middle Triassic to Middle Jurassic rifting in the Tethyan domain, followed by Middle to Late Jurassic spreading.

Shearing of syn-sedimentary carbonate breccia along strike-slip faults, Altamura Fm., Southern Italy

Fault breccia present along strike-slip faults was studied by mean of an integrated field and laboratory investigation. In particular, samples of sheared pre-existing, syn-sedimentary gravitative breccia were detailed studied in order to decipher the deformation mechanisms associated to strike-slip faulting. The sheared gravitative breccia is made up of matrix-supported, monomictic, unsorted intraformational fragments embedded within a reddish hematiterich, clayish matrix. Microsparry calcite cement is also present around the limestone fragments. In contrast, tectonic breccia consists of comminuted limestone fragments embedded in a calcite-rich matrix also including small amounts of reddish matrix. Particle shape analysis of representative images of the study hand specimens shows a variability of the box-counting dimension (D0-value) between the two different types of breccias, which can be explained in terms of peculiar strain localization within a threefold aggregate that characterizes the gravitative breccia, which is made up of calcite fragments, clayish matrix and very minute oxides.

Mineralogy and petrology of the metasedimentary rocks from the Frido Unit (southern Apennines, Italy)

This work concerns the development of a multidisciplinary research on metasedimentary rocks from the Frido Unit (southern Apennines) in the central Mediterranean area, based on petrographic study, mineralogical analysis and distribution of the major and trace elements. It aims at evaluating the paleoweathering conditions and provenance composition of the source area(s) of both shales and calcschists from the Frido Unit. Shales and calcschists underwent similar HP/LT overprint, by the occurrence of aragonite, as also shown by mineralogical analysis. The mineralogical composition of the studied rocks closely related to the geochemical variations, as shown by the negative correlation of CaO with other elements, due to the dilution effects by the carbonates, and the positive correlation of Al with most of the major and trace elements mainly related to the mica-like clay minerals. Elemental ratios, such as the Chemical Index of Alteration (CIA) and the Index of Compositional Variability (ICV), indicate low to moderate degree of chemical weathering a relatively immature source area(s) and, thus, first-cycle deposits related to tectonically active settings. Furthermore, the distribution of some major and trace elements suggest a provenance for the studied samples from source(s) composed of both felsic and mafic rocks.

Blueschist metamorphism of metabasite dykes in the serpentinites of the Frido Unit, Pollino Massif

Metamorphic evolution of metabasite dykes included in tectonic slices of serpentinites in ophiolitic rocks from Frido Unit (Pollino Massif) is reported.Petrological analysis via PT pseudo-sections calculation using Theriak-Domino software have been done for the system Na2O-CaOK2O-MgO-FeO-Al2O3SiO2-H2O (NCKMFASH) and showed that the pressure and temperature conditions of blueschist metamorphism are estimated to 8-12 kbar and 300-400 °C. The minerals in the metabasite dykes are chemically homogeneous, suggesting that they are almost completely equilibrated. The retrograde metamorphic evolution of the metabasites from high- to intermediate-pressure conditions is documented by the occurrence of minerals belonging to pumpellyite facies assemblages.High-pressure metamorphism in blueschist facies condition is related to the subduction of Frido Unit in low gradient conditions. The use of pseudosections stepwise controlled by petrographic observations allowed to estimate the P-T conditions in metabasite dykes.

Genesis of carbonate-rich veins in the serpentinites at the Calabria-Lucania boundary (southern Apennines)

In the northern sector of the Pollino massif (southern Apennines, Italy) well-exposed lens-shaped bodies of serpentinites and sediments of the Frido Unit belonging to the Liguride Complex crop-out. Most serpentinite rocks are cross-cut by carbonate and quartz-carbonate veins with different thickness. This study focuses on petrographic, mineralogical, geochemical, and isotopic analysis of the carbonate veins embedded in serpentinite rocks, collected at the Fosso Arcangelo site and at the Pietrapica quarry (Calabria-Lucanian boundary). The paragenesis of the carbonate veins from the Fosso Arcangelo site is dominantly made by calcite and aragonite with minor amount of rhodochrosite. In quartz-carbonate veins from Pietrapica quarry, dolomite, Mg-calcite, quartz, with minor ankerite were observed.The δ13CV-PDB isotope ratios of carbonates in the carbonate veins are in the range from +2.16‰ to -3.66‰ and corresponding δ18OV-SMOW values are between +15.02‰ and +21.53‰. The δ13CV-PDB values of carbonates in quartz-carbonate veins are in the range from -3.60‰ to -1.78‰ and the corresponding δ18OV-SMOW average value is around +21.3‰. The results suggest that the carbonate at both site occurredunder the same environmental conditions from crustal-derived andlow-moderate temperatures hydrothermal fluids having different chemical composition.