1,721,004 research outputs found
The key role of μH2O gradients in deciphering microstructures and mineral assemblages of mylonites: examples from the Calabria polymetamorphic terrane
No full textA careful petrologic analysis of mylonites’ mineral assemblages is crucial for a thorough comprehension of the rheologic behaviour of ductile shear zones active during an orogenesis. In this view, understanding the way new minerals form in rocks sheared in a ductile manner and why relict porphyroblasts are preserved in zones where mineral reactions are generally supposed to be deformation-assisted, is essential. To this goal, the role of chemical potential gradients, particularly that of H2O (μH2O), was examined here through phase equilibrium modelling of syn-kinematic mineral assemblages developed in three distinct mylonites from the Calabria polymetamorphic terrane. Results revealed that gradients in chemical potentials have effects on the mineral assemblages of the studied mylonites, and that new syn-kinematic minerals formed in higher-μH2O conditions than the surroundings. In each case study, the banded fabric of the mylonites is related to the fluid availability in the system, with the fluid that was internally generated by the breakdown of OH-bearing minerals. The gradients in μH2O favoured the origin of bands enriched in hydrated minerals alternated with bands where anhydrous minerals were preserved even during exhumation. Thermodynamic modelling highlights that during the prograde stage of metamorphism, high-μH2O was necessary to form new minerals while relict, anhydrous porphyroblasts remained stable in condition of low-μH2O even during exhumation. Hence, the approach used in this contribution is an in-depth investigation of the fluid-present/-deficient conditions that affected mylonites during their activity, and provides a more robust interpretation of their microstructures, finally helping to explain the rheologic behaviour of ductile shear zones
Residual stress on AISI 300 sintered materials: effect of thickness
No full textSelective Laser Melting (SLM) is one of the most interesting technologies in the rapid prototyping processes because it allows to build complex 3D metal parts. Moreover, full density can be reached and mechanical properties are similar to those obtained with conventional manufacturing processes. However, the most important drawback is related to the thermal transient encountered during solidification which generates highly variable residual thermal stresses in SLM parts. Parameters such as laser power, scanning strategy and velocity should be optimized also in order to allow full melting of the powders used in the process and minimize residual stresses that are strictly dependent on the manufacturing process and cannot be completely avoided. Geometry of parts should be optimized in order to keep residual stresses and distortions low. The aim of this paper is to investigate on residual stress distribution in SLM rectangular plates built by means of a new scanning strategy, implemented by dividing the fused zone in very small square sectors. The strain gauge hole drilling method is used to measure residual stress profiles in a set of test samples manufactured from the AISI Maraging 300 steel and characterized by different thickness. An analysis is performed in order to investigate the effect of thickness, position on the building platform and of distance from the surface of the specimens coming from the same process parameters on maximum and minimum principal residual stresses. The experimental results show that the melting/ solidification mechanism generates highly variable thermal residual stresses in the SLM parts used in this study
Agronomic evaluation and essential oil content of garlic (Allium sativum L.) ecotypes grown in Southern Italy.
No full textThe Curinga–Girifalco Line in the framework of the tectonic evolution of the remnant Alpine chain in Calabria (southern Italy)
No full textIn the peri-Mediterranean metamorphic belts, the tectonic evolution of the Calabria–Peloritani terrane during the dominant compressive tectonics of the Eocene represents one of the most problematic points in palinspastic restorations. A matter of particular debate is its shortening, which could have occurred during the Alpine or the Apennine subduction. In this regard, a crucial joint is provided by the kinematics of one of the most relevant shear zones such as the Curinga–Girifalco Line, cropping out in central Calabria. This shear zone juxtaposed a nearly complete Hercynian crustal section (i.e. the Sila and Serre Unit) onto the remnants of the Castagna Unit. The data in the available literature on ductile kinematics from the south-eastern branch of the Curinga–Girifalco Line indicate a downward movement of the hanging wall. In the present paper we show new, ductile kinematic data and petrographic evidence from outcrops in the north-western and south-eastern branches of the Curinga–Girifalco Line. Our results highlight the coherent kinematics of the Eocene shortening during the Alpine subduction system, followed by (late Eocene?)Oligocene to early Miocene, dominantly ductile extensional reworking, relating to the Apennines subduction system
Agronomic evaluation and essential oil content of garlic (Allium sativum L.) ecotypes grown in Southern Italy
No full textPRELIMINARY STUDY ON Fe360 WELDED SPECIMEN FATIGUE BEHAVIOR BY LOCAL STRAIN APPROACH AND ACOUSTIC EMISSIONS
No full textBuilding an orogen: Review of U-Pb zircon ages from the calabria-peloritani terrane to constrain the timing of the southern variscan belt
Full text linkThe application of zircon dating to the reconstruction of orogenic systems is invaluable since time constraints of the geological evolution of orogens are crucial for the proposal of geodynamic and paleogeographic models. Zircon is one of the most promising accessory minerals in geochronology of crystalline basements because of its high-closure temperature. Moreover, U-Pb data of relict and recrystallized grains indicate the maximum sedimentation age as well as the timing of metamorphism in metasediments. In addition, the U-Pb ages of magmatic zircons constrain the timescale of magmatism. The Calabria-Peloritani terrane (CPT) represents a key area in the Southern Variscan Belt, whose reconstruction is still unresolved. Therefore, a review of literature zircon age data accompanied with new data from six samples of orthogneisses, paragneisses, amphibolites, and actinolite schists, helps to constrain the evolution of this Cadomian fragment, affected by metamorphic and magmatic Variscan events. A revisiting of the timing of the geological events from Paleo-proterozoic to Permian is revealed by comparing the internal textures of zircons and their U-Pb age clusters. The detected age peaks at 2500 Ma, 1600 Ma, and 1000 Ma in the CPT were related to a provenance from West and East Gondwana realms. A sedimentation age around 630 Ma emerges for the middle-deep crust terranes of the CPT, affected by Ediacaran (579- 540 Ma) intrusions, accompanied by metamorphism dated at 556-509 Ma in the host metasediments. In the following, during Ordovician-Silurian extensional tectonics, the former Cadomian terranes were at least locally affected by fluid-assisted metamorphism (around 450 Ma) whereas the upper extensional basins that formed, were infilled by sediments along with interspersed volcanic to subvolcanic products. All these pre-Silurian terranes were involved in the subduction process of the Palaeotethys-Gondwana margin beneath Laurussia. The compressive phase began around 347 Ma, with under-thrusting of the formerly Gondwana substrate that was subjected to middle-high grade metamorphism, while the Ordovician-Silurian sediments were scraped off along the front of the Southern Variscan Belt and affected by low-grade metamorphism. Decompression of the whole Variscan orogenic system started around 320 Ma, together with uplifting of the chain and emplacement of widespread granitic intrusions which ended around 280 Ma and completed the Variscan orogenic cycle in the CPT
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