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1.
Mauro Lo Cascio Yan Liang Nobumichi Shimizu Paul C. Hess 《Contributions to Mineralogy and Petrology》2008,156(1):87-102
The grain-scale processes of peridotite melting were examined at 1,340°C and 1.5 GPa using reaction couples formed by juxtaposing
pre-synthesized clinopyroxenite against pre-synthesized orthopyroxenite or harzburgite in graphite and platinum-lined molybdenum
capsules. Reaction between the clinopyroxene and orthopyroxene-rich aggregates produces a melt-enriched, orthopyroxene-free,
olivine + clinopyroxene reactive boundary layer. Major and trace element abundance in clinopyroxene vary systematically across
the reactive boundary layer with compositional trends similar to the published clinopyroxene core-to-rim compositional variations
in the bulk lherzolite partial melting studies conducted at similar P–T conditions. The growth of the reactive boundary layer takes place at the expense of the orthopyroxenite or harzburgite and
is consistent with grain-scale processes that involve dissolution, precipitation, reprecipitation, and diffusive exchange
between the interstitial melt and surrounding crystals. An important consequence of dissolution–reprecipitation during crystal-melt
interaction is the dramatic decrease in diffusive reequilibration time between coexisting minerals and melt. This effect is
especially important for high charged, slow diffusing cations during peridotite melting and melt-rock reaction. Apparent clinopyroxene-melt
partition coefficients for REE, Sr, Y, Ti, and Zr, measured from reprecipitated clinopyroxene and coexisting melt in the reactive
boundary layer, approach their equilibrium values reported in the literature. Disequilibrium melting models based on volume
diffusion in solid limited mechanism are likely to significantly underestimate the rates at which major and trace elements
in residual minerals reequilibrate with their surrounding melt.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
2.
Roberto Danovaro Mauro Fabiano Giancarlo Albertelli Norberto Della Croce 《Marine Ecology》1995,16(2):103-116
Abstract. Quantitative information on the vertical distribution of meiofaunal abundances and biomass were obtained from samples collected at 3 bathyal stations in the Eastern Mediterranean Sea located at the same depth but characterized by different food supply. Vertical distribution patterns of nieiofauna were investigated in relation to the biochemical composition of the sediment organic matter (proteins, carbohydrates, and lipids) and compared to benthic bacterial standing stocks. No significant relationship between bacteria and meiofauna was found, whereas a significant relationship between protein and lipid concentrations and total meiofauna density was observed. These data suggest that labile organic matter. considered as material readily aVdihbk to benthic consumers, may be an important factor regulating meiofaunal abundance and vertical distribution in deep-sea sediments. 相似文献
3.
Sixteen mucilages sampled in the Adriatic and Tyrrhenian seas during 1999–2001 were characterised using spectroscopic [Fourier transform infrared spectroscopy (FTIR); colorimetric], chromatographic [thin-layer chromatography (TLC)], and elemental analysis techniques. Most samples contained comparable fractions of organic and inorganic compounds, with the exception of a few samples where the inorganic fraction was greater than the organic fraction. Carbohydrates were important in the samples rich in organic matter, while carbonate and silica (quartz and biogenic silica) were the most important constituents of the inorganic fraction. Carbonate and silica were the only important constituents of the samples with a very low organic content.According to chemical analyses, mucilage aggregates show the typical structure of humin—the insoluble fraction of the humic substance. Classification of mucilage samples as humin-like compounds, together with a reexamination of the factors involved in the formation of organic aggregates in marine environment, has led to the formulation of a reasonable hypothesis for mucilage formation. 相似文献
4.
Mauro Cacace Ulf Bayer Anna Maria Marotta 《International Journal of Earth Sciences》2008,97(5):899-913
The large-scale crustal deformations observed in the Central European Basin System (CEBS) are the result of the interplay
between several controlling factors, among which lateral rheological heterogeneities play a key role. We present a finite-element
integral thin sheet model of stress and strain distribution within the CEBS. Unlike many previous models, this study is based
on thermo-mechanical data to quantify the impact of lateral contrasts on the tectonic deformation. Elasto-plastic material
behaviour is used for both the mantle and the crust, and the effects of the sedimentary fill are also investigated. The consistency
of model results is ensured through comparisons with observed data. The results resemble the present-day dynamics and kinematics
when: (1) a weak granite-like lower crust below the Elbe Fault System is modelled in contrast to a stronger lower crust in
the area extending north of the Elbe Line throughout the Baltic region; and (2) a transition domain in the upper mantle is
considered between the shallow mantle of the Variscan domain and the deep mantle beneath the East European Craton (EEC), extending
from the Elbe Line in the south till the Tornquist Zone. The strain localizations observed along these structural contrasts
strongly enhance the dominant role played by large structural domains in stiffening the propagation of tectonic deformation
and in controlling the basin formation and the evolution in the CEBS. 相似文献
5.
Isotope geochemistry of caliche developed on basalt 总被引:1,自引:0,他引:1
Enormous variations in oxygen and carbon isotopes occur in caliche developed on < 3 Ma basalts in 3 volcanic fields in Arizona, significantly extending the range of δ18O and δ13C observed in terrestrial caliche. Within each volcanic field, δ18O is broadly co-variant with δ13C and increases as δ13C increases. The most 18O and 13C enriched samples are for subaerial calcite developed on pinnacles, knobs, and flow lobes that protrude above tephra and soil. The most 18O and 13C depleted samples are for pedogenic carbonate developed in soil atmospheres. The pedogenic caliche has δ18O fixed by normal precipitation in local meteoric waters at ambient temperatures and has low δ13C characteristic of microbial soil CO2. Subaerial caliche has formed from 18O-rich evapoconcentrated meteoric waters that dried out on surfaces after local rains. The associated 13C enrichment is due either to removal of 12C by photosynthesizers in the evaporating drops or to kinetic isotope effects associated with evaporation. Caliche on basalt lava flows thus initially forms with the isotopic signature of evaporation and is subsequently over-layered during burial by calcite carrying the isotopic signature of the soil environment. The large change in carbon isotope composition in subsequent soil calcite defines an isotopic biosignature that should have developed in martian examples if Mars had a “warm, wet” early period and photosynthesizing microbes were present in the early soils. The approach can be similarly applied to terrestrial Precambrian paleocaliche in the search for the earliest record of life on land. Large variations reported for δ18O of carbonate in Martian meteorite ALH84001 do not necessarily require high temperatures, playa lakes, or flood runoff if the carbonate is an example of altered martian caliche. 相似文献
6.
7.
8.
Alessandro Comunian Leonardo De Micheli Claudio Lazzati Fabrizio Felletti Francesca Giacobbo Mauro Giudici Riccardo Bersezio 《Hydrogeology Journal》2016,24(2):319-334
The fine-scale heterogeneity of porous media affects the large-scale transport of solutes and contaminants in groundwater and it can be reproduced by means of several geostatistical simulation tools. However, including the available geological information in these tools is often cumbersome. A hierarchical simulation procedure based on a binary tree is proposed and tested on two real-world blocks of alluvial sediments, of a few cubic meters volume, that represent small-scale aquifer analogs. The procedure is implemented using the sequential indicator simulation, but it is so general that it can be adapted to various geostatistical simulation tools, improving their capability to incorporate geological information, i.e., the sedimentological and architectural characterization of heterogeneity. When compared with a standard sequential indicator approach on bi-dimensional simulations, in terms of proportions and connectivity indicators, the proposed procedure yields reliable results, closer to the reference observations. Different ensembles of three-dimensional simulations based on different hierarchical sequences are used to perform numerical experiments of conservative solute transport and to obtain ensembles of equivalent pore velocity and dispersion coefficient at the scale length of the blocks (meter). Their statistics are used to estimate the impact of the variability of the transport properties of the simulated blocks on contaminant transport modeled on bigger domains (hectometer). This is investigated with a one-dimensional transport modeling based on the Kolmogorov-Dmitriev theory of branching stochastic processes. Applying the proposed approach with diverse binary trees and different simulation settings provides a great flexibility, which is revealed by the differences in the breakthrough curves. 相似文献
9.
10.
Jalal Samia Arnaud Temme Arnold K. Bregt Jakob Wallinga John Stuiver Fausto Guzzetti Francesca Ardizzone Mauro Rossi 《Landslides》2018,15(11):2129-2144
Landslide susceptibility modelling—a crucial step towards the assessment of landslide hazard and risk—has hitherto not included the local, transient effects of previous landslides on susceptibility. In this contribution, we implement such transient effects, which we term “landslide path dependency”, for the first time. Two landslide path dependency variables are used to characterise transient effects: a variable reflecting how likely it is that an earlier landslide will have a follow-up landslide and a variable reflecting the decay of transient effects over time. These two landslide path dependency variables are considered in addition to a large set of conditioning attributes conventionally used in landslide susceptibility. Three logistic regression models were trained and tested fitted to landslide occurrence data from a multi-temporal landslide inventory: (1) a model with only conventional variables, (2) a model with conventional plus landslide path dependency variables, and (3) a model with only landslide path dependency variables. We compare the model performances, differences in the number, coefficient and significance of the selected variables, and the differences in the resulting susceptibility maps. Although the landslide path dependency variables are highly significant and have impacts on the importance of other variables, the performance of the models and the susceptibility maps do not substantially differ between conventional and conventional plus path dependent models. The path dependent landslide susceptibility model, with only two explanatory variables, has lower model performance, and differently patterned susceptibility map than the two other models. A simple landslide susceptibility model using only DEM-derived variables and landslide path dependency variables performs better than the path dependent landslide susceptibility model, and almost as well as the model with conventional plus landslide path dependency variables—while avoiding the need for hard-to-measure variables such as land use or lithology. Although the predictive power of landslide path dependency variables is lower than those of the most important conventional variables, our findings provide a clear incentive to further explore landslide path dependency effects and their potential role in landslide susceptibility modelling. 相似文献