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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 occurrence 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. Estimates 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. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: The Calabride nappe is the uppermost structural element of the Calabria–Peloritani Arc, it consists of a Variscan continental crust section intruded by late-Variscan granitoids, on which a Mesozoic syn-rift sedimentary cover was deposited. The deepest part of the Variscan continental section crops out in Northern Catena Costiera. The transition from crustal to mantle-derived rocks is often marked by gabbros. P–T estimates for gabbro emplacement have been calculated applying conventional thermobarometry and a mean crystallization temperature of about 800°C at pressures between ~0.46 and 0.65GPa has been determined. Gabbro emplacement occurs at the base of the crust, during a low-pressure granulitic stage that affected the country rocks at the end of an isothermal decompression. The gabbros can be classified as tholeiites with MORB affinity. In situ LA-ICP-MS U–Pb analyses have been performed on zircons from representative samples of gabbro. U–Pb concordia ages range from 224±4Ma to 296±6Ma. Two age populations of middle–early Permian and middle Triassic age, respectively, seem to document the magmatic activity responsible for gabbros intrusion. According to cathodoluminescent images and REE pattern of zircon, the early Permian age refers to a metamorphic inherited core. Lithospheric thinning and a positive thermal anomaly, related to the exhumation of the deepest portion of the continental lithosphere, can explain the post-Variscan metamorphic evolution of the Calabride lithosphere and the underplating gabbroic magmatism. Since the major episode of gabbro emplacement is Triassic, this event could be related to the continental rifting that led to the opening of the Jurassic Tethys and Alpine cycle. [Copyright &y& Elsevier]

A comprehensive study of pebbles from the 'Salento-type' allochthnous bauxite deposit (Otranto, southern Italy), originally derived from a pristine Campanian bauxite, has been performed for evaluating: 1) the chemical fractionation and inter-elemental relationships, especially for critical elements, 2) the climatic conditions that promoted bauxite formation, and 3) the provenance of the protolith(s) using zircon age data and conservative elemental proxies. The study confirms the capability of bauxite to concentrate many elements defined as critical by the European Union report on critical raw materials. Sc, Co, Ga, and especially Cr, are enriched when compared with the UCC composition and assuming Nb is immobile. Other critical elements such as the REEs, with the exception of La, are moderately depleted. R-mode factor analysis suggests that most of the variance in our chemical dataset is explained by a factor with significant weightings for TiO 2 , Al 2 O 3 , Fe 2 O 3 , Sc, V, Nb, REEs, Pb and Th. This arises from climate effects affecting the distribution of the more abundant oxides and some trace elements, including the critical metals Nb and REEs. The texture of the pebbles is typical for Apulian karst bauxites and consists of sub-spheroidal ooids composed of boehmite and dispersed in a fine-grained matrix. The growth of the ooids, which formed under dry climate, was described in terms of fractal geometry. The average fractal dimension value of the ooids in the pebbles is close to that of the diffusion-limited aggregation models suggesting the ooid growth can be modelled using a molecular diffusion pattern, based on Fick's first law. The calculated time required for growth of the boehmite concretions is ~ 45 ÷ 310 ka. This finding is consistent with an intra-Campanian emersion event (74–76 Ma) that occurred during a dry and warm climatic stage. Since most of the karst bauxites worldwide have an ooidic texture, evaluation of the composition of concretions and the time required for their growth represents a powerful tool in reconstructing the palaeoenvironment. The zircon grains collected from the pebbles of the Salento-type karst bauxite define several concordant age populations. The youngest cluster, Early Cretaceous in age (99 ÷ 127.5 Ma), suggests that windborne particles from Cretaceous volcanics, possibly originating in the Carpatho-Balkan orogenic belts, provided material for further bauxitisation. The largest cluster (623 ÷ 689 Ma) is of Neoproterozoic age, predominately from the Late Ediacaran and Cryogenian p.p.. The 900–540 Ma Pan-African orogenic cycle was followed by continental-scale uplift and erosion, leading to the deposition of thick Cambrian–Ordovician siliciclastic sequences that represent the most widespread detrital sequence ever deposited on continental crust and that now cover large parts of North Africa. These Cambrian–Ordovician sandstones contain a large population of Neoproterozoic zircons of Cryogenian age. Neoproterozoic zircons also occur in the youngest (Silurian–Mesozoic) sandstones of the Saharan Metacraton. These sandstones also contain 1.0 Ga detrital zircons, suggesting as the oldest zircons found in the Salento-type bauxite pebbles (866 Ma and 941 Ma in age) are younger representatives of the zircon cluster present in this sandstone unit. These zircon age determinations suggest that the source material for the Salento-type bauxite pebbles was a combination of magmatic material from a distant source and clastic material derived from a continental margin (North Africa). This result concurs with the Eu/Eu* vs. Sm/Nd binary diagram, on which bauxite pebbles fall close to a mixing curve with andesite and cratonic sandstone end-members. As our results indicate that material was sourced from the North African continental margin, we suggest that a continental bridge separated oceanic domains in the Late Cretaceous of the Peri-Tethyan domain. [ABSTRACT FROM AUTHOR]