1,721,085 research outputs found
Clockwise and anticlockwise P-T path in the axial zone of the Variscan Sardinia-Corsica block
No full textRecent petrological studies on the Axial Zone of the Variscan chain have revealed the occurrence of anticlockwise P-T trajectories in metamorphic rocks from Corsica and Sardinia. These new findings, at first glance, appears to be in contrast with the clockwise P-T paths classically described for several high-pressure metamorphic rocks from the Variscan Sardinia - Corsica block in the last decades.
For the first time in Variscan Corsica, Massonne et al. (2018) described the anticlockwise P-T path of micaschists from the Porto Vecchio region. These rocks underwent prograde metamorphism starting at 3 kbar/600°C and then reached peak metamorphic conditions at 7 kbar/600-630°C. The Porto Vecchio micaschists are bordered to the north by the Solenzara-Fautea metamorphic rock unit that is, in turn, characterized by migmatites and granulites that underwent a clockwise P-T loop related to burial of continental crust to high-pressure (1.8–1.4 GPa) followed by high- to ultrahigh-temperature conditions (900–1000 °C; Giacomini et al., 2008). New, preliminary results on these rocks reveal that these latter peak temperatures could be probably significantly lower than those above mentioned, but there is no doubt about the clockwise shape of their P-T path. In the neighbouring Variscan terrains of north-eastern Sardinia, Scodina et al. (2019) reconstructed the P-T history of an amphibolite body whose burial path started at 0.8 GPa and was then followed by a slight increase in temperature up to peak metamorphic conditions of 1.3–1.4 GPa/690–740 °C. These amphibolites are hosted by migmatites for which a clockwise P-T path, related to a nearly isothermal exhumation, is widely accepted in the literature and confirmed by the most recent studies (Massonne et al., 2013 and references therein). In conclusion, it thus appears that during the Variscan collision, rock slices of different crustal levels were brought together and metamorphic rocks from upper and lower plates were involved in a particle path along an exhumation channel.
Giacomini F., Dallai L., Carminati E., Tiepolo M. & Ghezzo C. 2008. Exhumation of a Variscan orogenic complex: Insights into the composite granulitic–amphibolitic metamorphic basement of southeast Corsica (France).J. Metam. Geol., 26, 403–436.
Massonne H.-J., Cruciani G. & Franceschelli M. 2013. Geothermobarometry on anatectic melts - a high-pressure Variscan migmatite from northeast Sardinia. Int. Geol. Rev., 55, 1490–1505.
Massonne H.-J., Cruciani G., Franceschelli M. & Musumeci G. 2018. Anticlockwise pressure–temperature paths record Variscan upper-plate exhumation: example from micaschists of the Porto Vecchio region, Corsica. J. Metam. Geol., 36, 55–77.
Scodina M., Cruciani G., Franceschelli M. & Massonne H.-J. 2019. Anticlockwise P-T evolution of amphibolites from NE Sardinia, Italy: geodynamic implications for the tectonic evolution of the Variscan Corsica-Sardinia block. Lithos, 324–325, 763–775
Zoning of chloritoid from kyanite facies rocks, Alpi Apuane, Italy
No full textChloritoid with significant Mg-Fe zoning occurs as lath-shaped porphyroblasts and as clusters of subradiating crystals in the Triassic Verrucano metapsammite (quartz + muscovite + chlorite + chloritoid ± kyanite) of the Massa Unit, Alpi Apuane. Two main types of chloritoid zoning profiles were found. The first type is characterised by gradual increase in Mg from core to rim of the porphyroblasts. In the second type the Mg content is constant from the core to the inner rim, but sharply decreases in the outer rim. Both types of zoning have been interpreted as the result of prograde growth during the Alpine metamorphism. The temperature, estimated using the chlorite-chloritoid thermometer, ranges from 467 to 560°C
Two stage of garnet growth in mylonitic micaschist from NE Sardinia: evidence from major and trace elements in garnet
No full textMylonitic micaschists in the south-eastern sector of the Posada-Asinara Shear Zone in the Axial Zone of the Sardinia Variscan consist of garnet porphyroblasts associated with plagioclase, quartz, biotite, staurolite, white mica, and chloritoid. The garnet porphyroblasts, enveloped by the S2 schistosity, preserve an internal foliation identified by the alignment of quartz, sometimes arranged into a sigmoidal pattern suggesting rotation of the garnet during growth. Major element compositional variation follows a bell-shaped zoning profile with Ca and Mn contents progressively decreasing, and Fe and Mg increasing, from the core (Alm45Grs25 Prp1Sps29) to the outer rim domain (Alm86Grs3Prp11Sps1; Cruciani et al., 2022). LA-ICPMS trace element mapping revealed
that the boundary between core and rim is marked by a thin annulus enriched in Y and HREE. The garnet core consists of an inner and an outer zone where the maximum concentration of elements from Lu to Tb progressively moves outwards with decreasing atomic number. This trend continues in the rim outside the annulus, where a further distinction between a Sm -, Eu-, Gd-, Tb-rich inner rim and a REE-poor outer rim was
observed (Franceschelli et al., 2023). The P-T path of the mylonitic micaschist, which was reconstructed from major element zoning in garnet, and from K-white mica composition and mineral assemblage preserved in garnet, is clockwise, subdivided into two different stages. The P-T trajectory was refined by the Compositional Zoning in Garnet and its Modification by diffusion software by Faryad and Ježek (2019). The garnet growth occurred into two stages, marked by partial resorption of the garnet core. The first stage of the P-T path is a prograde segment up to the peak pressure (T 430–490°C, P 1.3–1.4 GPa) whereas the second one reflects garnet rim growth and staurolite formation at peak metamorphism (560–630 °C/0.6–1.1 GPa) followed by exhumation
P-T conditions of garnet-staurolite-bearing schists from Variscan NE Sardinia (Italy)
No full textIn north-eastern Sardinia, in the southern side of the Posada-Valley which is a km-wide shear zone of regional relevance, we collected garnet-staurolite schists with plurimillimetric garnet and staurolite porphyroblasts. At the outcrop scale the schists appears as silver-coloured, strongly foliated rocks rich in mica characterized by the occurrence of reddish to brownish garnet porphyroblasts up to 0.8-1 cm in size. Garnet crystals are enveloped by the main S2 regional schistosity which is identified by the orientation of white mica and chlorite. The garnet porphyroblasts are characterized by an inclusion-rich nucleus (garnet core) surrounded by a garnet mantle almost free of inclusions. The
inclusions within the garnet crystals, which mainly consist of quartz, rutile, ilmenite, chloritoid, mica and zircon, often follow an oriented spiral-shaped and/or sigmoidal arrangement recording an earlier S1 schistosity. Some smaller (less than 0.5 cm) and/or anhedral garnet grains lack the inclusion rich nucleus. The yellowish staurolite porphyroblasts (up to 0.5 cm in size) are often characterized by opaque minerals oriented inclusions. Chloritoid is found as oriented and isolated single crystals within the rock matrix. Paragonite locally grows on chloritoid, when this latter is included in the
garnet. Accessory minerals in the schists are apatite and tourmaline. EMP X-ray mapping and rim-core-rim garnet compositional profiles reveal a strong compositional zoning of the garnet components and the occurrence of a very thin (only a few dozens of μm in size) outern garnet rim, not detectable with the polarizing microscope. The garnet core composition ranges between XCa (Ca/(Ca+Mg+Fe+Mn): 0.21-0.27; XMg (Mg/(Ca+Mg+Fe+Mn): 0.01-0.02; XFe (Fe/(Ca+Mg+Fe+Mn): 0.45-0.50; XMn (Mn/(Ca+Mg+Fe+Mn): 0.25-0.30. The garnet mantle is enriched in almandine (XFe
0.55-85), pyrope (XMg 0.018-0.075) and depleted in grossular (XCa 0.06-0.18) and spessartine (XMn 0.05-0.24) components as compared to the garnet core. The narrow outern rim shows an abrupt decrease in grossular (XCa 0.02-0.03) and increase in pyrope content (XMg 0.11-0.13). Plagioclase single crystals in the matrix are oligoclase/albite (Ab ca. 90 mol.%). Staurolite porphyroblasts show XMg ratio of 0.14-0.13 in the core and 0.11-0.10 in the rim. Ti and Mn
contents in staurolite is 0.1 and 0.02-0.05 a.p.f.u, respectively. Chloritoid, independently from its microstructural position (i.e. inside the garnet or in the rock matrix) shows XMg ratio of 0.12-0.13. Biotite in the matrix has XMg ratio of 0.47. White mica shows different composition based on the microstructural position: white mica included in garnet has Si (a.p.f.u.) 6.38 and XMg 0.54, white mica single crystals in the matrix shows Si 6.11 a.p.f.u. and XMg 0.47, white mica in the micaceous layers has Si 6.04 a.p.f.u. and XMg 0.40. Chlorite shows XMg 0.4. Monazite in situ dating with
EMP yielded ages comprised between 417 and 322 Ma (average 377 Ma) for monazite included in garnet and 402-330 Ma (average 357 Ma) for monazite in the rock matrix. Small rutile grains preserved in garnet contain up to 0.02 wt.% zirconium, whereas the rare rutile grains in the rock matrix have undetectable zirconium content. Application of the Zr-in-rutile thermometer, following the calibration after [1], to 35 rutile grains included in garnet gives an average temperature of 557°C. Preliminary results on thermodynamic modelling suggest that the schist underwent a clockwise P-T path with a prograde portion that reached ca. 1.0 GPa peak pressure and temperature up to 600°C. The rock underwent later low-grade re-equilibration and mylonitization.
References:
[1] Tomkins et al. (2007) J Metamorphic Geol 25:703–71
b0 of muscovite in low and high variance assemblages from low grade Verrucano rocks, Northern Apennines, Italy
No full textA note on the occurrence and chemistry and K/Ar data of stilpnomelane from Mt. Contrario (Apuan Alps, Northern Tuscany)
No full textDynamic Resilient Containment Control in Multirobot Systems
Full text linkIn this article, we study the dynamic resilient containment control problem for continuous-time multirobot systems (MRSs), i.e., the problem of designing a local interaction protocol that drives a set of robots, namely the followers, toward a region delimited by the positions of another set of robots, namely the leaders, under the presence of adversarial robots in the network. In our setting, all robots are anonymous, i.e., they do not recognize the identity or class of other robots. We consider as adversarial all those robots that intentionally or accidentally try to disrupt the objective of the MRS, e.g., robots that are being hijacked by a cyber–physical attack or have experienced a fault. Under specific topological conditions defined by the notion of (r,s)-robustness, our control strategy is proven to be successful in driving the followers toward the target region, namely a hypercube, in finite time. It is also proven that the followers cannot escape the moving containment area despite the persistent influence of anonymous adversarial robots. Numerical results with a team of 44 robots are provided to corroborate the theoretical findings
Ca-distribution between almandine-rich garnet and plagioclase in pelitic and psammitic schists from the metamorphic basement of north-eastern Sardinia
No full textGarnet and plagioclase pairs from fourteen selected samples, from garnet to sillimanite zones, collected along a NS traverse throughout the metamorphic basement of NE Sardinia, have been analyzed by microprobe. Beyond the garnet isograd, plagioclase has albitic composition and the garnet (a Ca-rich almandine) shows Ca/ Ca+Mg+Fe ratios of about 0.35-0.30, fairly constant from core to rim. Towards the North, still in the garnet zone, when on the large albitic core of plagioclase a thin and discontinuous oligoclasic rim (An22-An18) formed, we observe in the garnet edge an abrupt decrease of the Ca/Ca+Mg+Fe ratio (0.27-0.16). In the staurolite and sillimanite zones garnet does not show significant Ca-zoning and it is characterized by low Ca content (Ca/Ca+Mg+Fe<0.1); the coexisting plagioclase has oligoclasic (An16-An27) composition. The chemical data and the microstructural evidence on growth time indicate that the garnet and plagioclase had a strong mutual interference in determining the relative Ca distribution. The most relevant reactions are discussed and, in particular, the antipathetical Ca-zoning, recorded by garnet and plagioclase in the garnet zone, is considered as the evidence of temperature increase during growth of the two minerals. It is also suggested that the sharp variation of Ca content at the garnet edge was controlled by the discontinuous nature of plagioclase solid solution in the "peristeritic" range. The order of appearance of garnet and oligoclase in the basement of NE Sardinia is also discussed in comparison with other well known metamorphic sequence (Vermont, New Zealand and Dalradian). It is concluded that the different order of appearance is controlled other than the different nature of the calcic phases in the lower grade zones also by the {Mathematical expression} in the fluid phase. © 1982 Springer-Verlag
Multi-Agent Coordination of Thermostatically Controlled Loads by Smart Power Sockets for Electric Demand Side Management
No full textThis article presents a multi-agent control architecture and an online optimization method based on a dynamic average consensus to coordinate the power consumption of a large population of thermostatically controlled loads (TCLs). Our objective is to penalize peaks of power demand, smooth the load profile, and enable demand-side management. The proposed architecture and methods exploit only local measurements of power consumption via smart power sockets (SPSs) with no access to their internal temperature. No centralized aggregator of information is exploited, and agents preserve their privacy by cooperating anonymously only through consensus-based distributed estimation. The interactions among devices occur through an unstructured peer-to-peer (P2P) network over the Internet. Methods for parameter identification, state estimation, and mixed logical modeling of TCLs and SPSs are included. The architecture is designed from a multi-agent and plug-and-play perspective, in which existing household appliances can interact with each other in an urban environment. Finally, a novel low-cost testbed is proposed along with numerical tests and experimental validation
A Heuristic approach for Online Distributed Optimization of Multi-Agent Networks of Smart Sockets and Thermostatically Controlled Loads based on Dynamic Average Consensus
No full textThis paper presents a novel heuristic online optimization method and multi-agent control architecture to optimize the Peak-to-Average power Ratio (PAR) of a large population of Thermostatically Controlled Loads (TCLs) over a sliding receding horizon time window. The proposed architecture exploits only local measurements of the TCL power consumption with no knowledge of their internal temperature. No centralized aggregator of information is used and agents preserve their privacy by cooperating only through consensus-based distributed estimation. TCLs interactions occur via Smart Power Sockets (SPSs) which are interconnected through a peer-to-peer (P2P) network over the internet. The control architecture is designed from a multi-agent perspective in which real household appliances can interact with each other via SPSs.Our contribution is twofold: first we introduce a novel hybrid modelling of the TCL-plus-SPS system along with a method for parameter identification and a method estimate the internal state of the TLC through SPS performed power measurements; then we provide a heuristic algorithm for online distributed optimization of the on/off states of the SPSs which exploits a dynamic average consensus algorithm to estimate the planned future average power consumption of the network while preserving the agents' privacy. Numerical simulations and preliminary experimental results performed in a novel low cost testbed are provided
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