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71.
Maria?Rosaria?RennaEmail author Riccardo?Tribuzio 《Contributions to Mineralogy and Petrology》2009,157(6):813-835
Spinel pyroxenites occur locally as clasts in polygenic breccias from the Late Cretaceous sedimentary mélanges of the Northern
Apennine (Italy). They are of cumulus origin and formed in the deep crust by early precipitation of clinopyroxene and minor
olivine and late crystallisation of orthopyroxene, spinel, Ti-pargasite and sulphides. Pyroxenites underwent high-temperature
(~850°C) subsolidus re-equilibration and ductile deformation with development of mylonitic bands made of clinopyroxene, orthopyroxene,
Ti-pargasite and spinel. U–Pb geochronology on zircons revealed the occurrence of inherited grains of Early Proterozoic to
Late Devonian age. The inherited zircons are locally rimmed by recrystallised zircon domains. The oldest rims yield a mean
concordia U–Pb age at 306 ± 8 Ma, which is considered to date the emplacement of the pyroxenites, in the framework of the
post-Variscan lithospheric extension. The incompatible element compositions of calculated melts in equilibrium with clinopyroxenes
from the pyroxenites are characterised by Ba, Nb, LREE and Sr enrichment relative to N-MORB. The depleted Nd isotopic signature
of the pyroxenites (initial εNd values of +5.3 to +6.1) may be thus linked to primary magmas produced by low degrees of melting of asthenospheric mantle.
In addition, the pyroxenites locally record the infiltration of plagioclase-saturated hydrous melts, most likely evolved through
fractional crystallisation and enriched in highly incompatible elements, within the clinopyroxene-dominated crystal mush.
A thermal event in Late Permian–Middle Triassic caused the partial resetting of zircon U–Pb system. 相似文献
72.
The Finero phlogopite-peridotite massif: an example of subduction-related metasomatism 总被引:13,自引:0,他引:13
Alberto Zanetti Maurizio Mazzucchelli Giorgio Rivalenti Riccardo Vannucci 《Contributions to Mineralogy and Petrology》1999,134(2-3):107-122
The Finero peridotite massif is a harzburgite that suffered a dramatic metasomatic enrichment resulting in the pervasive
presence of amphibole and phlogopite and in the sporadic occurrence of apatite and carbonate (dolomite)-bearing domains. Pyroxenite
(websterite) dykes also contain phlogopite and amphibole, but are rare. Peridotite bulk-rock composition retained highly depleted
major element characteristics, but was enriched in K, Rb, Ba, Sr, LREE (light rare earth elements) (LaN/YbN = 8–17) and depleted in Nb. It has high radiogenic Sr (87Sr/86Sr(270) = 0.7055–0.7093), low radiogenic Nd (ɛNd(270) = −1 to −3) and EMII-like Pb isotopes. Two pyroxenite – peridotite sections examined in detail show the virtual absence of
major and trace element gradients in the mineral phases. In both rock types, pyroxenes and olivines have the most unfertile
major element composition observed in Ivrea peridotites, spinels are the richest in Cr, and amphibole is pargasite. Clinopyroxenes
exhibit LREE-enriched patterns (LaN/YbN ∼16), negative Ti and Zr and generally positive Sr anomaly. Amphibole has similar characteristics, except a weak negative
Sr anomaly, but incompatible element concentration ∼1.9 (Sr) to ∼7.9 (Ti) times higher than that of coexisting clinopyroxene.
Marked geochemical gradients occur toward apatite and carbonate-bearing domains which are randomly distributed in both the
sections examined. In these regions, pyroxenes and amphibole (edenite) are lower in mg## and higher in Na2O, and spinels and phlogopite are richer in Cr2O3. Both the mineral assemblage and the incompatible trace element characteristics of the mineral phases recall the typical
signatures of “carbonatite” metasomatism (HFSE depletion, Sr, LILE and LREE enrichment). Clinopyroxene has higher REE and
Sr concentrations than amphibole (amph/cpxDREE,Sr = 0.7–0.9) and lower Ti and Zr concentrations. It is proposed that the petrographic and geochemical features observed at
Finero are consistent with a subduction environment. The lack of chemical gradients between pyroxenite and peridotite is explained
by a model where melts derived from an eclogite-facies slab infiltrate the overhanging harzburgitic mantle wedge and, because
of the special thermal structure of subduction zones, become heated to the temperature of the peridotite. If the resulting
temperature is above that of the incipient melting of the hydrous peridotite system, the slab-derived melt equilibrates with
the harzburgite and a crystal mush consisting of harzburgite and a silica saturated, hydrous melt is formed. During cooling,
the crystal mush crystallizes producing the observed sequence of mineral phases and their observed chemical characteristics.
In this context pyroxenites are regions of higher concentration of the melt in equilibrium with the harzburgite and not passage-ways
through which exotic melts percolated. Only negligible chemical gradients can appear as an effect of the crystallization process,
which also accounts for the high amphibole/clinopyroxene incompatible trace element ratios. The major element refractory composition
is explained by an initially high peridotite/melt ratio. The apatite, carbonate-bearing domains are the result of the presence
of some CO2 in the slab-derived melt. The CO2/H2O ratio in the peridotite mush increased by crystallization of hydrous phases (amphibole and phlogopite) locally resulting
in the unmixing of a late carbonate fluid. The proposed scenario is consistent with subduction of probably Variscan age and
with the occurrence of modal metasomatism before peridotite incorporation in the crust.
Received: 20 July 1998 / Accepted: 28 October 1998 相似文献
73.
74.
Geophysical interpretation of a high-resolution seismic refraction profile in the Northern Apennines
Giancarlo Biella Roberto De Franco Martina Demartin Riccardo Barzaghi Fernando Sanso Domenico Sguerso 《地学学报》1994,6(1):45-53
A combined seismic and gravimetric interpretation in the Northern Apennines area (Italy) is presented. To the knowledge of the authors, this is one of the few attempts to apply tomographic methodology to a seismic refraction profile. This procedure, together with the classical interpretation for defining lower reflectors, led to the formulation of quite an accurate model of the upper crust. A gravity analysis was performed concurrently taking into account the seismic results at different depths which correspond to different frequency domains in the gravity signal. While the medium- and high-frequency patterns have been solved by trial-and-error, the regional trend has been modelled applying the collocation procedure to the gravity data. 相似文献
75.
Riccardo Tortini Fabio L. Bonali Claudia Corazzato Simon A. Carn Alessandro Tibaldi 《地学学报》2014,26(4):273-281
Measuring surface deformation is critical in analogue modelling of Earth science phenomena. Here, we present a novel application of the Microsoft Kinect sensor to measure vertical deformation in a scaled analogue model of Nisyros volcano (Greece), simulating two magmatic sources and related surface deformation. The Kinect permits capture of real time, 640 × 480 pixel, true‐colour images (RGB) and a grid of distances to the modelled surface with a horizontal and vertical resolution of ±1 mm. Using recorded distances permits quantification of vertical deformation in terms of maximum and average down‐ and uplift during deflation and inflation phases respectively, which is of crucial importance for defining the kinematics of faults formed during the modelling, determined from interpretation of the RGB images. Although other techniques have demonstrated similar or higher accuracy, our study demonstrates the cost‐effectiveness of the Kinect in analogue modelling of volcanoes. 相似文献
76.
Valerio Bellucci Riccardo Camattari Vincenzo Guidi Ilaria Neri Nicolas Barri��re 《Experimental Astronomy》2011,31(1):45-58
Silicon mono-crystals have been bent thanks to a series of parallel superficial indentations on one of the largest faces of the crystals. This technique relies on irreversible compression of the crystal beneath and beside the indentations. This latter causes deformation with no need for external device, resulting in a uniform self-standing curvature within the crystal. Indented Si crystals have been characterized at European Synchrotron Radiation Facility using a monochromatic beam ranging from 150 to 700 keV. Crystals exhibited very high diffraction efficiency over a broad range of energy, peaking 95% at 150 keV. Measured angular spread of the diffracted beam was always very close to the morphological curvature of the sample under investigation, proving that the energy passband of bent crystals can be controlled by simply imparting a selected curvature to the sample. The method of superficial indentations was found to offer high reproducibility and easy control of diffraction properties of the crystals. Moreover the method is cheap and simple, being based on mass production tools. A Laue lens made of crystals bent by superficial indentations can provide high-efficiency concentration of hard x-ray photons, leading significant improvement in many astrophysical applications. 相似文献
77.
Claudio Di Celma Riccardo Teloni Andrea Rustichelli 《International Journal of Earth Sciences》2014,103(3):843-875
The Monte Ascensione succession (c. 2.65–2.1 Ma) is a well-exposed example of an exhumed submarine canyon fill embedded within slope hemipelagic mudstones. This gorge represented a long-lasting pathway for sediment transport and deposition and during the Gelasian delivered Apennine-derived clastic sediment to the adjacent Peri-Adriatic basin. A total of six principal lithofacies types, representing both canyon-confining hemipelagic deposits and canyon-filling turbidity current and mass-transport deposits, can be delineated in the studied sedimentary succession. The canyon-fill deposits display a marked cyclic character and the component lithofacies succeed one another to form at least fifteen fining-upward stratal units, which are interpreted to represent high-frequency, unconformity-bounded depositional sequences. Variability in the vertical repetition of constituent lithofacies allows the identification of three basic styles of sequence architecture that can be interpreted in terms of differing positions along a conceptual down-canyon depositional profile. An integrated chronology, based on biostratigraphic data and on palaeomagnetic polarity measurements, strongly supports a one-to-one correlation between the sequence-bounding surfaces and oxygen isotope stages G2–78, suggesting that the most feasible sequence-engendering mechanism is that of orbitally dictated glacio-eustatic changes in sea level, which regulated timing of sediment storage on the shelf and its redistribution beyond the shelf edge. One of the most significant aspects of this study is the demonstration that processes occurring within upper slope canyons can be expected to be strongly influenced by variations in sea level; that is, the erosional and depositional features evident in these deposits can be strongly controlled by allocyclic processes rather than autocyclic or random processes. 相似文献
78.
Riccardo Bevilacqua Jason S. Hall Marcello Romano 《Celestial Mechanics and Dynamical Astronomy》2010,106(1):69-88
A novel two-phase hybrid controller is proposed to optimize propellant consumption during multiple spacecraft rendezvous maneuvers
in Low Earth Orbit. This controller exploits generated differentials in aerodynamic drag on each involved chaser spacecraft
to effect a propellant-free trajectory near to the target spacecraft during the first phase of the maneuver, and then uses
a fuel optimal control strategy via continuous low-thrust engines to effect a precision dock during the second phase. In particular,
by varying the imparted aerodynamic drag force on each of the chaser spacecraft, relative differential accelerations are generated
between each chaser and the target spacecraft along two of the three translational degrees of freedom. In order to generate
this required differential, each chaser spacecraft is assumed to include a system of rotating flat panels. Additionally, each
chaser spacecraft is assumed to have continuous low-thrust capability along the three translational degrees of freedom and
full-axis attitude control. Sample simulations are presented to support the validity and robustness of the proposed hybrid
controller to variations in the atmospheric density along with different spacecraft masses and ballistic coefficients. Furthermore,
the proposed hybrid controller is validated against a complete nonlinear orbital model to include relative navigation errors
typical of carrier-phase differential GPS (CDGPS). Limitations of the proposed controller appear relative to the target spacecraft’s
orbit eccentricity and a general characterization of the atmospheric density. Bounds on these variables are included to provide
a framework within which the proposed hybrid controller can effect an extremely low propellant rendezvous of multiple chaser
spacecraft to a desired target spacecraft. 相似文献
79.
The Ligurian Alps segment of the Alpine–Apennine orogen in NW Italy is unconformably covered by Upper Eocene to Holocene sediments in the Tertiary Piedmont Basin (TPB) and Po Plain. These sediments dip towards the north demonstrating the erosional nature of the southern border of the succession and implying that the adjacent orogenic belt formed the substratum rather than the margin of the sedimentary basin. Apatite (U–Th)/He and fission track thermochronology shows that the orogen first subsided and was buried at >4 km from 30 to 26 Ma and began its exhumation thereafter. From 26 Ma to present, this upward movement was contemporaneous with subsidence in the northern TPB. The couple exhumation in the S and subsidence in the N migrated northwards through time. Vertical movements in the area are similar to those reconstructed in Corsica. In both cases, the onset of exhumation becomes younger away from the Ligurian‐Provençal basin and has little correlation with the opening of the surrounding oceanic basins. 相似文献
80.
Riccardo Campana Mauro Orlandini Ettore Del Monte Marco Feroci Filippo Frontera 《Experimental Astronomy》2014,37(3):599-613
Low-inclination, low altitude Earth orbits (LEO) are of increasing importance for astrophysical satellites, due to their low background environment. Here, the South Atlantic Anomaly (SAA) is the region with the highest amount of radiation. We study the radiation environment in a LEO (500–600 km altitude, 4° inclination) through the particle background measured by the Particle Monitor (PM) experiment onboard the BeppoSAX satellite, between 1996 and 2002. Using time series of particle count rates measured by PM we construct intensity maps and derive SAA passage times and fluences. The low-latitude SAA regions are found to have an intensity strongly decreasing with altitude and dependent on the magnetic rigidity. The SAA extent, westward drift and strength vs altitude is shown. 相似文献