Relationships between the Tertiary structural evolution of the Sardinia-Corsica-Provençal Domain and the Northern Apennines     

Luigi Carmignani  F. Antonio Decandia  Leonardo Disperati  P. Lorenzo Fantozzi  Antonio Lazzarotto  Domenico Liotta  Giacomo Oggiano 《地学学报》1995,7(2):128-137

Based on a revision of stratigraphic and structural data relative to the Balearic basin, the Corsica-Sardinia massif, the Northern Tyrrhenian Sea and the Northern Apennines the following new hypothesis is proposed for the area located between the Sardinian-Corsican-Provençal and Northern Apennines regions: (a) convergence with subduction of oceanic crust under the Iberian plate beginning in the Late Cretaceous; (b) continental collision in the Oligocene-Aquitanian, with development of the Northern Apennines belt and transpressive deformation in a hinterland that consisted of the Corsica-Sardinia massif (still attached to the Iberian plate); (c) in the Burdigalian the tectonic regime changed from compressive to extensional. During this period the Corsica-Sardinia massif migrated contemporaneously with opening of the Balearic basin, the Sardinian rift, and the Northern Tyrrhenian sea; (d) from the Burdigalian to the present, there was contemporaneous compression at the front and extension at the back of the Northern Apennines chain; both these features progressively migrated toward the east. The coeval extension and compression is attributed to lithospheric delamination toward the external part of the belt.  相似文献   

Cultural heritage and geological hazards: the case of the Calomini hermitage in Tuscany (Italy)   总被引：1，自引：0，他引：1  

Giacomo D’Amato Avanzi  Daria Marchetti  Alberto Puccinelli 《Landslides》2006,3(4):331-340

The Calomini hermitage is located on a steep slope, below an 80- to 130-m-high hanging rock wall. The hermitage, a significant example of religious architecture, has been a pilgrimage place since the Middle Ages. The monastery, completed by the tenth century, is built into the rock mass for more than half of its length. The stability and safety of the complex are threatened by stability problems in the rock slope. Structural and geotechnical investigations were carried out, showing the potential for rock blocks slides, particularly under dynamic conditions, with the fall of middle size blocks. Recently, some remedial works have been carried out, and wire meshes have been hung on the rock wall. Nevertheless, a significant portion of the Calomini hermitage area may be still dangerous and exposed to severe landslide hazard. Therefore, further research and countermeasures are necessary to protect a very important item of Italian cultural and architectural heritage.  相似文献   

Xenoliths and microxenoliths in H chondrites: Sampling the zodiacal cloud in the asteroid Main Belt     

Giacomo BRIANI  Matthieu GOUNELLE  Michèle BOUROT‐DENISE  Michael E. ZOLENSKY 《Meteoritics & planetary science》2012,47(5):880-902

Abstract– Xenoliths are inclusions of a given meteorite group embedded in host meteorites of a different group. Xenoliths with dimensions between a few μm and about 1 mm (microxenoliths) are “meteorite‐trapped” analogues of micrometeorites collected on the Earth. However, they have the unique features of sampling the zodiacal cloud (1) at more ancient times than those sampled by micrometeorites and (2) at larger distances from the Sun (corresponding to the asteroid Main Belt) than that sampled by micrometeorites (1 AU). Herein we describe a systematic search for new xenoliths and microxenoliths in H chondrites, aimed at determining their abundance in these ordinary chondrites, analyzing their mineralogy, and searching for possible correlations with host meteorite properties. Sixty‐six sections from 40 meteorites have been analyzed. Twenty‐four new xenoliths have been discovered. About 87% of them are microxenoliths (i.e., <1 mm), only three are >1 mm in their largest dimension. All the newly discovered xenoliths and microxenoliths are composed of carbonaceous chondritic material. Hence, the zodiacal cloud was dominated by carbonaceous material even in past epochs. All the new xenoliths and microxenoliths have been found in regolith breccias. Hydrous‐phase‐rich xenoliths and microxenoliths in H4 and H5 chondrites attest that their embedding happened after the end of the thermal metamorphism. All these data suggest that xenoliths and microxenoliths were embedded when their host meteorites were part of the parent body regolith. This, combined with the H chondrite impact age distribution, attests that the embedding may have happened as early as 3.5 Gyr ago.  相似文献   

Behaviour of Fe<Subscript>4</Subscript>O<Subscript>5</Subscript>–Mg<Subscript>2</Subscript>Fe<Subscript>2</Subscript>O<Subscript>5</Subscript> solid solutions and their relation to coexisting Mg–Fe silicates and oxide phases     

Laura?Uenver-ThieleEmail author  Alan?B.?Woodland  Nobuyoshi?Miyajima  Tiziana?Boffa?Ballaran  Daniel?J.?Frost 《Contributions to Mineralogy and Petrology》2018,173(3):20

Experiments at high pressures and temperatures were carried out (1) to investigate the crystal-chemical behaviour of Fe₄O₅–Mg₂Fe₂O₅ solid solutions and (2) to explore the phase relations involving (Mg,Fe)₂Fe₂O₅ (denoted as O₅-phase) and Mg–Fe silicates. Multi-anvil experiments were performed at 11–20 GPa and 1100–1600 °C using different starting compositions including two that were Si-bearing. In Si-free experiments the O₅-phase coexists with Fe₂O₃, hp-(Mg,Fe)Fe₂O₄, (Mg,Fe)₃Fe₄O₉ or an unquenchable phase of different stoichiometry. Si-bearing experiments yielded phase assemblages consisting of the O₅-phase together with olivine, wadsleyite or ringwoodite, majoritic garnet or Fe³⁺-bearing phase B. However, (Mg,Fe)₂Fe₂O₅ does not incorporate Si. Electron microprobe analyses revealed that phase B incorporates significant amounts of Fe²⁺ and Fe³⁺ (at least ~?1.0 cations Fe per formula unit). Fe-L_2,3-edge energy-loss near-edge structure spectra confirm the presence of ferric iron [Fe³⁺/Fe_tot?=?~?0.41(4)] and indicate substitution according to the following charge-balanced exchange: [4]Si⁴⁺?+?[6]Mg²⁺?=?2Fe³⁺. The ability to accommodate Fe²⁺ and Fe³⁺ makes this potential “water-storing” mineral interesting since such substitutions should enlarge its stability field. The thermodynamic properties of Mg₂Fe₂O₅ have been refined, yielding H°_1bar,298?=???1981.5 kJ mol^??1. Solid solution is complete across the Fe₄O₅–Mg₂Fe₂O₅ binary. Molar volume decreases essentially linearly with increasing Mg content, consistent with ideal mixing behaviour. The partitioning of Mg and Fe²⁺ with silicates indicates that (Mg,Fe)₂Fe₂O₅ has a strong preference for Fe²⁺. Modelling of partitioning with olivine is consistent with the O₅-phase exhibiting ideal mixing behaviour. Mg–Fe²⁺ partitioning between (Mg,Fe)₂Fe₂O₅ and ringwoodite or wadsleyite is influenced by the presence of Fe³⁺ and OH incorporation in the silicate phases.  相似文献   

Reliability of water content estimation by profile probe and its effect on slope stability     

Lucio Di Matteo  Cristina Pauselli  Daniela Valigi  Maurizio Ercoli  Mauro Rossi  Giacomo Guerra  Costanza Cambi  Remo Ricco  Giuseppe Vinti 《Landslides》2018,15(1):173-180

Shallow landslide failures are distributed worldwide and cause economic losses and fatalities. A proper evaluation of the possible occurrence of shallow landslides requires reliable characterization of water content. Volumetric water content (θ) is commonly estimated using dielectric sensors, which use manufacturers’ calibration curves developed for specific soil types. In this study, we present the experimental results achieved during a laboratory calibration of a capacitance probe (PR2/6 probe), tested on two sandy soils widely outcropping in Central Italy. The proposed equations demonstrate a more reliable estimation of θ with respect to the generalized soil equation provided by the manufacturer, which overestimates θ by up to 10 percentage points. Such overestimation could affect the evaluation of suction stress in partially saturated shallow soils affecting the slope stability analysis. Although the use of θ from correct calibration equations provides less precautionary factor of safety values, a reliable evaluation of the soil moisture condition is fundamental when mapping and predicting the spatial and temporal occurrence of shallow landslides. The use of the PR2/6 probe with the appropriate soil calibration equations in early warning monitoring systems will provide a more reliable forecast, minimizing the number of false alarms.  相似文献   

Evidence for an asteroid–comet continuum from simulations of carbonaceous microxenolith dynamical evolution     

Giacomo BRIANI  Alessandro MORBIDELLI  Matthieu GOUNELLE  David NESVORNÝ 《Meteoritics & planetary science》2011,46(12):1863-1877

Abstract– Micrometeoroids with 100 and 200 μm size dominate the zodiacal cloud dust. Such samples can be studied as micrometeorites, after their passage through the Earth atmosphere, or as microxenoliths, i.e., submillimetric meteorite inclusions. Microxenoliths are samples of the zodiacal cloud dust present in the asteroid Main Belt hundreds of millions years ago. Carbonaceous microxenoliths represent the majority of observed microxenoliths. They have been studied in detail in howardites and H chondrites. We investigate the role of carbonaceous asteroids and Jupiter‐family comets as carbonaceous microxenolith parent bodies. The probability of low velocity collisions of asteroidal and cometary micrometeoroids with selected asteroids is computed, starting from the micrometeoroid steady‐state orbital distributions obtained by dynamical simulations. We selected possible parent bodies of howardites (Vesta) and H chondrites (Hebe, Flora, Eunomia, Koronis, Maria) as target asteroids. Estimates of the asteroidal and cometary micrometeoroid mass between 2 and 4 AU from the Sun are used to compute the micrometeoroid mass influx on each target. The results show that all the target asteroids (except Koronis) receive the same amount (within the uncertainties) of asteroidal and cometary micrometeoroids. Therefore, both these populations should be observed among howardite and H chondrite carbonaceous microxenoliths. However, this is not the case: carbonaceous microxenoliths show differences similar to those existing among different groups of carbonaceous chondrites (e.g., CI, CM, CR) but two sharply distinct populations are not observed. Our results and the observations can be reconciled assuming the existence of a continuum of mineralogical and chemical properties between carbonaceous asteroids and comets.  相似文献   

Crystal structure of columbite under high pressure     

Serena C. Tarantino  Michele Zema  Tiziana Boffa Ballaran 《Physics and Chemistry of Minerals》2010,37(10):769-778

The structural evolution of two columbites under pressure, one ferrocolumbite from Raode (Africa) and one manganocolumbite from Kragero (Norway), has been determined by single-crystal X-ray diffraction. Structural investigations at high pressure have been carried out on samples which were preliminarily annealed to attain the complete cation-ordered state. For each crystal, five complete datasets have been collected from room pressure up to ca. 7 GPa. Structure refinements converged to final discrepancy factors R ranging between 5.2 and 5.8% for both the crystals. Structure refinements of X-ray diffraction data at different pressures allowed characterisation of the mechanisms by which the columbite structure accommodates variations in pressure. A and B octahedral volumes in both samples decrease linearly as pressure increases, with a larger compression of the larger A site. The difference in polyhedral bulk moduli of the A sites for the two samples does not appear to relate directly to the octahedral sizes, the A site being more compressible in the Fe-rich sample than in the Mn-rich one. By far the most compressible direction in both the analysed samples is along b. The cations are in fact free to move along this direction, thus allowing the octahedral chains to slide over each other; this effect is particularly evident in the manganocolumbite sample which shows a steep shortening of interchain A–B distances along b.  相似文献   

New stratigraphic and sedimentological investigations on the Middle Eocene–Early Miocene continental successions in southwestern Sardinia (Italy): Paleogeographic and geodynamic implications     

Sebastiano Barca  Luca Giacomo Costamagna 《Comptes Rendus Geoscience》2010,342(2):116-125

In SW Sardinia, the continental Tertiary successions referred up to now to the Cixerri Fm. (Middle Eocene–Lower Oligocene?) have been investigated. Sedimentological analysis suggests these deposits lied down in fluvial environments and comprised between distal braided streams passing eastward to meandering streams/coastal environments (?) under sub-arid climates. The scrutinization of the Cixerri Fm. westernmost successions allowed one to split locally the upper from the lower part based on sedimentological and mineralogical features and indirect dating. Unfortunately, this separation cannot be set everywhere. The few upper outcrops plainly evidenced and well-constrained have been newly named Flumentepido Fm. and assigned to Late Oligocene–Early Miocene: they figure out alluvial fans and proximal braided rivers. This way, the SW Sardinia Tertiary continental sedimentation extends its persistence, contemporaneously changing its tectostratigraphic meaning: from a molassoid context related to the Pyrenean wedge dismantling (Eocene–Oligocene) to a rift-margin succession connected with the opening of the Algero-Provençal back-arc basin due to the Apennine subduction in Oligocene–Miocene times.  相似文献   

Cooling and exhumation history of deep‐seated and shallow level,late Hercynian granitoids from Calabria     

Alfredo Caggianelli  Giacomo Prosser  Aldo Del Moro 《Geological Journal》2000,35(1):33-42

The thermal and exhumation history of late Hercynian granitoids from Calabria (Sila and Serre massifs) has been studied using thermobarometry and radiometric age determinations. The uplift and erosion which followed contractional tectonics of Tertiary age exposed in Calabria a nearly complete section of the Hercynian crust. Field data, constrained by igneous thermobarometrical data, have enabled us to draw simplified crustal profiles. In both the Sila and Serre massifs, granitoids make up the intermediate portions of the crustal sections and are stacked as tabular intrusions for up to 13 km cumulative thickness. Shallow granitoids are characterized by a weak fabric, mostly developed in the magmatic stage, whereas deep‐seated granitoids display a strong fabric developed in the magmatic state and, with decreasing temperatures, in the subsolidus state. The intrusive bodies were emplaced at 300–290 Ma, at a time when the Calabrian crust was undergoing extensional tectonics and crustal thinning. The subsequent post‐Hercynian evolution is recorded by Rb‐Sr dates of micas and fission track ages of zircon and apatite obtained from granitoids emplaced at different depths. A decrease in Rb‐Sr and fission track ages is observed as depth of emplacement increases. Data on the post‐Hercynian geological evolution of Calabria were used to model in three stages the cooling and exhumation history of deep‐seated and shallow granitoids. The first stage, in Permian to Triassic times, was characterized by slow erosion. It was followed by a second stage of extensional tectonics in Jurassic times. The third stage was exhumation during the Apenninic Orogeny. The model has generated two P–T–t arrays, one for deep‐seated and the other for shallow granitoids of the Serre massif. The T–t paths suggest that the dates of micas, zircon and apatite are cooling ages. They also show that deep‐seated granitoids remained at temperatures above the brittle–plastic transition for a long time, whereas shallow granitoids cooled rapidly. Distinct P–T–t paths explain why deep‐seated and shallow granitoids display different fabric and microstructural features. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献