Constitutive equations for drained cohesionless soils under triaxial stress states, based on a microslip model with internal friction, are proposed and applied to the analysis of the seismic response of soil deposits. The microslips, assumed localized in the discontinuity surfaces passing through the particle-to-particle contacts, describe the effects of the sliding and rolling between grains of sand. Once the response of the model under cyclic shearing stresses and strains superimposed on the geostatic stress state has been analysed, the constitutive equations are applied to a one-dimensional shear model for the dynamic analysis of the layered deposits. An application to an instrumented soil deposit is then developed, the experimental results of which refer to both strong and weak motion earthquakes; the comparisons between the experimental and theoretical results point out the peculiarities and validity limits of the model. The model here developed may be applied also to the analysis of two- and three-dimensional sites. 相似文献
Fifty-seven Antarctic marine bacteria were examined for their ability to degrade commercial diesel oil as the sole organic substrate at both 4 °C and 20 °C. Based on the preliminary screening, two isolates (B11 and B15) with high capacity to degrade diesel oil were selected and their biodegradation efficiency was quantified by gas chromatographic analysis. As expected for psychrotrophs, diesel oil biodegradation was slower at 4 °C than at 20 °C. The two strains also mineralized the C28 n-paraffin octacosane at 20 °C and polychlorinated biphenyls (PCBs) at 4 °C and 20 °C. 相似文献
DaG 896 is an olivine-rich microporphyritic rock of komatiitic composition. Both the olivine composition (Fa17.5±2.1, [Mn/Mg] = 0.0061) and the bulk oxygen isotopic composition (δ17O = +2.55, δ18O = +3.50) indicate that DaG 896 is a sample of the H-chondrite parent body. The bulk chemistry shows an H-chondritic distribution of lithophile elements, whereas chalcophile and siderophile elements are strongly depleted, indicating formation through whole-rock melting (or nearly so) of H-chondrite material, nearly complete loss of the metal plus sulfide component, and crystallization without significant igneous fractionation. Superheated, severely shocked chondritic relics (∼10 vol%), typically in the form of corroded lithic fragments <100 μm in size intimately distributed within the igneous lithology, indicate that melting was triggered by a highly energetic impact, which possibly induced shock pressures of ∼80-100 GPa. The relatively young 3.704 ± 0.035 Ga 40Ar-39Ar crystallization age is consistent with the impact melting origin, as magmatism in the asteroid belt was active only in the first hundred million years of solar system history.Based on textural data and thermodynamic crystallization modelling, we infer that DaG 896 crystallized from a liquidus temperature of ∼1630°C under relatively slow cooling rates (∼10°C h−1) to ∼1300°C, before quenching. The two-stage cooling history indicates that a reasonable formation environment might be a dike intruding cooler basement below a crater floor. Metal-silicate fractionation may have been accomplished, at least at the centimeter-scale of the studied meteorite sample, through differential acceleration of immiscible liquids of different density during the intense flow regimes associated with the excavation and modification stages of the cratering mechanism. Alternatively, DaG 896 may represent a surface sample of a differentiated melt body at the floor of an impact crater, as gravitational settling appears to be an effective process at the surface of a chondritic parent asteroid: for metal particles 1 to 10 mm in size, typically observed in partially differentiated impact melt rocks, Stokes’ Law indicates a settling velocity >1 m h −1 during the first few hours of crystallization on asteroidal bodies of >25 km radius.The ∼3.7 Ga age of DaG 896 nearly overlaps with the slightly older resetting ages of H-chondrites (all impact melts) available from the literature, indicating that the H-chondrite parent asteroid underwent extensive impact melting at the enduring of the cataclysmic bombardment of the early solar system. Such an age overlap may also indicate early disruption of the initial H-chondrite parent asteroid.The close similarity between the bulk composition and degassing age of DaG 896 and silicate inclusions in IIE iron meteorites is further evidence in support of a common origin by impact melting and metal-silicate segregation on the H-chondrite parent asteroid. Our new high-precision oxygen isotopic measurements of H-chondrites (Δ17O = 0.77 ± 0.04) should be extended to IIEs to verify this possible petrogenetic link. 相似文献
Data supporting relevant Late Cretaceous–Early Eocene sinistral displacement along the Giudicarie fault zone and a minor Neogene dextral displacement along the Periadriatic lineament are discussed. The pre-Adamello structural belt is present only in the internal Lombardy zone, located W of the Adamello massif. This belt is unknown in the Dolomites and surrounding areas located to the E of the Giudicarie lineament. Upper Cretaceous–Early Eocene thick syntectonic Flysch deposits of Lombardy and Giudicarie are well preserved along the southern and eastern border of the pre-Adamello belt (S-vergent Alpine orogen). Towards the E, in the Dolomites and in the Carnic Alps and external Dinarides, only incomplete remnants of Flysch deposits, Aptian–Albian and Turonian–Maastrichtian in age, are present. They can be considered as equivalent to those of Lombardy and Giudicarie formerly in connection to each other along the N-Giudicarie corridor. To the S, the syntectonic Flysch deposits are laterally replaced by the calcareous red pelagites of the Scaglia Rossa and by the carbonate shelf deposits of the Friuli (to the E) and Bagnolo (to the S) carbonate platforms. The different location in the southern structural accretion of the eastern and western opposite blocks (the Dolomites versus the pre-Adamello belt) can be related to the Cretaceous–Eocene convergence. In this frame, the N-Giudicarie fault has been considered as part of a former transfer zone, which produced the sinistral lateral displacement of the Southern Alps front for an amount of some 50 km. During the Late Eocene to Early Oligocene the transfer zone was mostly sealed by the Paleogene Adamello batholith. Oligocene to Neogene compressional evolution inverted the N-Giudicarie fault into a backthrust of the Austroalpine units over the South-Alpine chain. 相似文献
We exploit observations at 1.25 mm with the ESO–SEST telescope of a southern galaxy sample, selected from the IRAS PSC and complete to S 60=2 Jy, to derive the FIR and mm luminosity functions and the conditional probability distributions of FIR and mm luminosity of galaxies. The reliability of these estimates is ensured by the good observed correlation of the far-infrared and mm emissions. This detailed knowledge of the millimetric properties of galaxies is used to simulate the extragalactic sub-mm sky (background intensity, small-scale anisotropy signals and discrete source statistics), which is the target of a variety of ground-based and space observatories. We find, in particular, that a recent tentative detection of a sub-mm background would require, if confirmed, strong evolution with cosmic time of the galaxy long-wavelength emissivity. We finally discuss ways to test such evolution with present and forthcoming facilities: while emphasizing the difficulty of achieving this with large mm telescopes on the ground (because of the poor atmospheric conditions of current sub-mm sites), we mention an interesting opportunity with the long-wavelength camera on ISO . Preliminary results of deep surveys, both from space and from the ground, seem indeed to require excess emission in the past by dusty galaxies with respect to no-evolution predictions. 相似文献
In situ Sr-isotope and microchemical studies were used to determine the provenance of K-feldspar megacrysts hosted in mafic alkaline potassic, ultrapotassic rocks and in differentiated rocks from two nearby volcanic apparatus in central Italy.
At Monte Cimino volcanic complex, mafic leucite-free ultrapotassic megacryst-bearing rocks of olivine latitic composition are associated with evolved latite and trachyte. Here, latites and trachytes straddle the sub-alkaline field. Age-corrected 87Sr/86Sr values (Sri) of the analysed Cimino olivine latites vary from 0.71330 and 0.71578 and strongly increase at constant Mg value. Latite and trachyte have lower Sri than olivine latites ranging between 0.71331 and 0.71361. Sri of K-feldspar megacrysts from olivine latites are between 0.71352 and 0.71397, but core and rim 87Sr/86Sr ratios within individual megacryst are indistinguishable. In all the mafic rocks, the megacrysts are not in isotopic equilibrium with the hosts. K-feldspar megacrysts from both the latite and trachyte have similar Sr-isotope compositions (Sri=0.71357–0.71401) to those in the olivine latites. However, Sri of megacryst in the trachyte vary significantly from core to rim (Sri from 0.71401 to 0.71383). As with the olivine latites, the K-feldspar megacrysts are not in isotopic equilibrium with bulk rock compositions of the latite or trachyte.
At Vico volcano, megacryst-bearing rocks are mafic leucite-free potassic rocks, mafic leucite-bearing ultrapotassic rocks and old trachytic rocks. The mafic leucite-bearing and leucite-free rocks are a tephri-phonolite and an olivine latite, respectively. A megacryst in Vico trachyte is isotopically homogeneous (Sri CORE=0.71129, RIM=0.71128) and in equilibrium with the host rock (Sri bulk ROCK=0.71125). Sri of megacryst from tephri-phonolite is clearly not in isotopic equilibrium with its host (Sri bulk ROCK=0.71158), and it increases from core (Sri=0.71063) to rim (Sri=0.71077). A megacryst in Vico olivine latite is isotopically homogeneous (Sri CORE=0.71066, RIM=0.71065), but not in equilibrium with the host rock (Sri bulk ROCK=0.71013).
The Sr isotope microdrilling technique reveals that Cimino megacrysts were crystallised in a Cimino trachytic magma and were subsequently incorporated by mixing/mingling processes in the latitic and olivine latitic melts. A model invoking the presence of a mafic sub-alkaline magma, which was mixed with the olivine latite, is proposed to justify the lack of simple geochemical mixing relation between Cimino trachytes and olivine latites. This magmatological model is able to explain the geochemical characteristics of Cimino olivine latites, otherwise ascribed to mantle heterogeneity.
The similarity of core Sri of megacrysts hosted in Vico tephri-phonolite and olivine latite suggests that the K-feldspar megacrysts are co-genetic. Isotopic equilibrium between megacryst and Vico host trachyte indicates that the trachyte is the parent of this megacryst. On the contrary, the megacrysts hosted in tephri-phonolite and olivine latite do not derive from the old trachytic magma because no diffusion process may explain the core to rim Sr isotope increase of the xenocryst hosted in the tephri-phonolite. The megacrysts hosted in the Vico mafic rocks might derive from a trachytic melt similar in composition to the old Vico trachytes. 相似文献
Thirty of the 58 groundwaters sampled in September-October 2000 in the study area (La Spezia Province, Italy) have Mg-HCO3 to Ca-HCO3 composition, undetectable Cr(III) contents, and virtually equal concentrations of total dissolved Cr and Cr(VI). Therefore, dissolved Cr is present in toto as Cr(VI), with concentrations of 5-73 ppb. These values are above the maximum permissible level for drinking waters (5 ppb). Local ophiolites, especially serpentinites and ultramafites, are Cr-rich and represent a Cr source for groundwaters. However, since Cr is present as Cr(III) in rock-forming minerals, its release to the aqueous solution requires oxidation of Cr(III) to Cr(VI). This can be performed by different electron acceptors, including Mn oxides, H2O2, gaseous O2, and perhaps Fe(III) oxyhydroxides. Based on this evidence and due to the absence of anthropogenic Cr sources, the comparatively high Cr(VI) concentrations measured in the waters of the study area are attributed to natural pollution. 相似文献
Summary Mineral compositions in leucite-bearing and leucite-free rocks from Vico volcano are reported. FeO/MgO partitioning (Kdol/liq) between olivine and latite (0.14–0.22), and between olivine and trachyte (0.06–0.10) indicates a lack of equilibrium between
mineral and host rock. This suggests that mingling and/or mixing between magmas was a leading process during magmatic differentiation.
In addition, a phono-tephrite olivine population with high (0.84) and equilibrium (0.23–0.29) Kdol/liq values has been produced by the interaction of differently evolved magmas. Zoning in clinopyroxene and plagioclase from these
rocks recorded the same processes. In addition, resorbed quartz xenocrysts with coronas of clinopyroxene microlites indicate
that digestion of crustal rocks occurred during the residence of magma in a shallow level reservoir. Increasing Fe coupled
with decreasing Ca in diopside crystals from some phonolites, together with the petrographic and trace element data, indicate
that polybaric fractional crystallisation also may be involved in the genesis of magmas of the second period of Vico activity.
Leucite-free trachybasalts erupted in a late stage contain highly forsteritic olivine phenocrysts (forsterite 84–88 mol.%)
in-equilibrium (Kdol/liq = 0.24–0.35) with the host rock, which indicate that they did not suffer chemical modification at low pressure.
Received November 28, 2000; revised version accepted September 27, 2001 相似文献
