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41.
Carla?TiraboschiEmail authorView authors OrcID profile Simone?Tumiati Dimitri?Sverjensky Thomas?Pettke Peter?Ulmer Stefano?Poli 《Contributions to Mineralogy and Petrology》2018,173(1):2
We experimentally investigated the dissolution of forsterite, enstatite and magnesite in graphite-saturated COH fluids, synthesized using a rocking piston cylinder apparatus at pressures from 1.0 to 2.1 GPa and temperatures from 700 to 1200 °C. Synthetic forsterite, enstatite, and nearly pure natural magnesite were used as starting materials. Redox conditions were buffered by Ni–NiO–H2O (ΔFMQ = ??0.21 to ??1.01), employing a double-capsule setting. Fluids, binary H2O–CO2 mixtures at the P, T, and fO2 conditions investigated, were generated from graphite, oxalic acid anhydrous (H2C2O4) and water. Their dissolved solute loads were analyzed through an improved version of the cryogenic technique, which takes into account the complexities associated with the presence of CO2-bearing fluids. The experimental data show that forsterite?+?enstatite solubility in H2O–CO2 fluids is higher compared to pure water, both in terms of dissolved silica (mSiO2?=?1.24 mol/kgH2O versus mSiO2?=?0.22 mol/kgH2O at P?=?1 GPa, T?=?800 °C) and magnesia (mMgO?=?1.08 mol/kgH2O versus mMgO?=?0.28 mol/kgH2O) probably due to the formation of organic C–Mg–Si complexes. Our experimental results show that at low temperature conditions, a graphite-saturated H2O–CO2 fluid interacting with a simplified model mantle composition, characterized by low MgO/SiO2 ratios, would lead to the formation of significant amounts of enstatite if solute concentrations are equal, while at higher temperatures these fluid, characterized by MgO/SiO2 ratios comparable with that of olivine, would be less effective in metasomatizing the surrounding rocks. However, the molality of COH fluids increases with pressure and temperature, and quintuplicates with respect to the carbon-free aqueous fluids. Therefore, the amount of fluid required to metasomatize the mantle decreases in the presence of carbon at high P–T conditions. COH fluids are thus effective carriers of C, Mg and Si in the mantle wedge up to the shallowest level of the upper mantle. 相似文献
42.
M. A. R. VASCONCELOS K. WÜNNEMANN A. P. CRÓSTA E. C. MOLINA W. U. REIMOLD E. YOKOYAMA 《Meteoritics & planetary science》2012,47(10):1659-1670
Forward modeling is commonly applied to gravity field data of impact structures to determine the main gravity anomaly sources. In this context, we have developed 2.5‐D gravity models of the Serra da Cangalha impact structure for the purpose of investigating geological bodies/structures underneath the crater. Interpretation of the models was supported by ground magnetic data acquired along profiles, as well as by high resolution aeromagnetic data. Ground magnetic data reveal the presence of short‐wavelength anomalies probably related to shallow magnetic sources that could have been emplaced during the cratering process. Aeromagnetic data show that the basement underneath the crater occurs at an average depth of about 1.9 km, whereas in the region beneath the central uplift it is raised to 0.5–1 km below the current surface. These depths are also supported by 2.5‐D gravity models showing a gentle relief for the basement beneath the central uplift area. Geophysical data were used to provide further constraints for numeral modeling of crater formation that provided important information on the structural modification that affected the rocks underneath the crater, as well as on shock‐induced modifications of target rocks. The results showed that the morphology is consistent with the current observations of the crater and that Serra da Cangalha was formed by a meteorite of approximately 1.4 km diameter striking at 12 km s?1. 相似文献
43.
Morphometry of micrite particles in cretaceous microporous limestones of the Middle East: Influence on reservoir properties 总被引:2,自引:0,他引:2
Matthieu Deville de Periere Christophe DurletEmmanuelle Vennin Laurent LambertRaphael Bourillot Bruno CalineEmmanuelle Poli 《Marine and Petroleum Geology》2011,28(9):1727-1750
Microporosity may account for a significant part of the total porosity of Cretaceous limestone reservoirs of the Middle East. In these microporous facies porosity is moderate to excellent (up to 35%) while permeability is poor to moderate (up to 190 mD). Micritic limestones also may form dense layers with very low porosity and permeability values.Micritic samples were collected from three fields of the Habshan and Mishrif Formations, to examine the spatial relationship with their porosity, permeability and pore throat radius distributions. Two key parameters of the micritic particles are studied using scanning electron microscopy: their morphology (shape and inter-crystal contacts), and their crystallometry.Results reveal that micrite matrixes can be subdivided into three petrophysical classes. Class C (strictly microporous limestones with coarse punctic-to-partially coalescent micrites) is made up of coarse (>2 μm) polyhedral to rounded micritic crystals, it has good to excellent porosity (8-28%), poor to moderate permeability (0.2-190 mD) and a mean pore threshold radius of more than 0.5 μm. The class C is usually observed in rudist shoal facies where relatively high hydrodynamic energy disfavoured deposition of the finer micritic crystals. It also developed within meteoric leaching intervals below exposure surfaces. Class F (strictly microporous limestones with fine punctic-to-partially coalescent micrites) is composed of fine (<2 μm) polyhedral to rounded micrites with poor to excellent porosity (3-35%), but permeability values of less than 10 mD and a mean pore threshold radius of less than 0.5 μm. It is mostly observed in sediments deposited in a low energy muddy inner platform setting. Class D (strictly microporous mud-dominated facies with compact anhedral to fused dense micrites) comprises subhedral to anhedral crystals with sutured contacts forming a dense matrix. It has very low porosity and permeability. Class D is only found in low energy muddy inner platform facies and forms inter-reservoir or caps rock layers in close association with stylolites and clay contents that usually exceed 10%. 相似文献
44.
L. Tositti M. Mingozzi S. Sandrini L. Forlani M.C. Buoso M. De Poli D. Ceccato D. Zafiropoulos 《Global and Planetary Change》2006,53(4):278
Two peat columns from Tunguska (Siberia) were analysed for pollen, spores, charcoal, trace elements and γ-emitters in order to identify the fingerprints of the impact of a still unidentified cosmic body (TCB), which occurred in the summer of 1908, and the level of environmental pollution in a background area of central Siberia. Peat layers were subject to non-destructive γ-ray spectrometry to derive radiochronology by the excess 210Pb method. The age-to-depth relationship was crosschecked by using both 1963 horizon of 137Cs associated to maximum global fallout deposition and palynological data profiles. Vertical distributions of trace elements in the peat columns were obtained by PIXE multielemental analysis allowing determination of the levels of environmental contamination in a background region of the Siberian taiga.The association of heavy metals such as Ni, Co and Cu in the profiles suggests the connection of the area with mining and metal smelting activity in the north of the region through atmospheric circulation. As concerns global scale contamination, the inventory of the artificial radionuclide 137Cs (4.6 kBq m− 2) shows a value typical of remote slightly contaminated areas resulting from global scale redistribution of radioactive fallout from Cold War nuclear weapon testing. The atmospheric inventory of the natural radionuclide 210Pb, for which a mean annual flux of 200 Bq m− 2 yr− 1 has been calculated, is typical of continental regions.The influence of Tunguska Cosmic Body in the peat is recognizable by a large discontinuity in the palynological profile of the peat monolith at a depth coinciding with the 1908 layer as determined by the 210Pb technique, showing a large peak of total pollen counting attributed to the impact of the shockwave on the area in which huge tree stands were destroyed. Following the event, tree pollen concentration decreases abruptly showing the temporary inception of a mire environment with an increase of Sphagnum spore concentrations. Results of elemental analysis so far available do not show anomalies in the concentration profiles at depths coinciding with the Tunguska event layer indicating the need for pre-concentration technique enabling the detection of element associations typical of extraterrestrial materials. 相似文献
45.
This paper describes numerical models of advection/diffusion between enclaves and host magmas, applied with the aim of estimating
time-scales during which enclaves can be homogenised. In particular, advection was simulated using a numerical system consisting
of regular and chaotic regions. Results indicate that the homogenisation time of enclaves in chaotic regions is several orders
of magnitude faster than in regular regions. For instance, an enclave with a diameter of 100 cm may be homogenised in the
chaotic region in ∼ 380 years, assuming an advection velocity of 10 cm/year, whereas in the regular region it would require
6.5×105 years for complete homogenisation. This implies that, in the same magmatic system, large differences in the degree of homogenisation
may co-exist, generating magmatic masses with large spatial and temporal inhomogeneities.
The results of this study may have significant petrological and volcanological implications. From a petrological point of
view, mafic enclaves dispersed in felsic host rocks are regarded as portions of mafic magma which, trapped inside regular
regions, survived the hybridisation process. Instead, host rocks are regarded as regions where efficient mixing dynamics generated
hybrid magmas. The fact that a single magmatic mass may display large compositional differences at the same time undermines
the assumption of most geochemical models, which assume the temporal and spatial homogeneity of the magma body. From the volcanological
perspective, the presence of magmatic enclaves in volcanic rocks allows us to estimate the mixing times of magmas by analysing
chemical diffusion patterns between host rocks and enclaves.
Editorial responsibility: D. Dingwell 相似文献
46.
47.
Landslide Representation Strategies in Susceptibility Studies using Weights-of-Evidence Modeling Technique 总被引:4,自引:0,他引:4
This paper is focused primarily on how to represent landslide scarp areas, how to analyze results achieved by the application
of specific strategies of representation and how to compare the outcomes derived by different tests, within a general framework
related to landslide susceptibility assessment. These topics are analyzed taking into account the scale of data survey (1:10,000)
and the role of a landslide susceptibility map into projects targeted toward the definition of prediction, prevention, and
mitigation measures, in a wider context of civil protection planning. These aims are achieved by using ArcSDM (Arc Spatial
Data Modeler), a software extension to ArcView GIS useful for developing spatial prediction models using regional datasets.
This extension requires a representation by points of the investigated problems (landslide susceptibility, aquifer vulnerability,
detection of mineral deposits, identification of natural habitats of animals, and plants, etc.). Maps of spatial evidence
from regional geological and geomorphological datasets were used to generate maps showing susceptibility to slope failures
in two different study areas, located in the northern Apennines and in the central Alps (Italy), respectively. The final susceptibility
maps for both study areas were derived by the application of the weights-of-evidence (WofE) modeling technique. By this method
a series of subjective decisions were required, strongly dependent on an understanding of the natural processes under study,
supported by statistical analysis of the spatial associations between known landslides and evidential themes. Except for maps
of attitude, permeability, and structure, that were not available for both study areas, the other data were the same and comprised
geological, land use, slope, and internal relief maps.
The paper illustrates how different representations of scarp areas by points (in terms of different number of points) did
not greatly influence the final response map, considering the scale of this work. On the contrary, some differences were observed
in the capability of the model to describe the relations between predictor variables and landslides. In effect, a representation
of the scarp areas using one point every 50 m led to a more efficient model able to better define relationships of this type.
It avoided both problems of redundancy of information, deriving by the use of too many points, and problems related to a random
positioning of the centroid. Moreover, it permitted to minimize the uncertainty related with identification and mapping of
landslides. 相似文献
48.
Summary A plethora of evidence indicates that magma mixing processes can take place at any evolutionary stage of magmatic systems
and that they are extremely common in both plutonic and volcanic environments. Furthermore, recent studies have shown that
the magma mixing process is governed by chaotic dynamics whose evolution in space and time generates complex compositional
patterns. The fact that magma mixing processes can produce igneous bodies exhibiting a large compositional complexity brings
up the key question about the potential pitfalls that may be associated with the sampling of these systems for petrological
studies. In particular, since commonly only exiguous portions of the whole magmatic system are available as outcrops for sampling,
it is important to address the point whether the sampling may be considered representative of the complexity of the magmatic
system. Here, we attempt to address this crucial point by performing numerical simulations of magma mixing processes in 3D,
and by evaluating the best conditions for sampling by considering different landscape morphologies and percentages of vegetation
cover. It is shown that the goodness of sampling is strongly dependant on the roughness of the landscape, with highly irregular
morphologies being the best candidates to give the most complete information on the whole magma body. Vegetation cover, on
the contrary, does not appear to significantly influence the representativeness of sampling. 相似文献
49.
Dario Visonà Anna Maria Fioretti Maria Eliana Poli Adriano Zanferrari Mark Fanning 《Swiss Journal of Geoscience》2007,100(2):313-324
The Athesian Volcanic District (AVD), a thick sequence of andesitic to rhyolitic lava and ignimbrite, overlies both the Variscan basement of the Dolomites and, where present, the continental basal conglomerate of Upper Carboniferous(?) to Early Permian age. This volcanic activity is known to mark the margin of the intra-Pangea megashear system between Gondwana and Laurasia, the onset age of which is determined in this study.SHRIMP U-Pb dating on zircon from Ponte Gardena/Waidbruck (Isarco/Eisack valley) basaltic andesite yields an age of 290.7 ± 3 Ma, providing the oldest record of andesite volcanic activity yet documented in the AVD. Two younger dates (279.9 ± 3.3 and 278.6 ± 3.1 Ma) obtained for the andesitic necks of M. dei Ginepri (Eores/Aferer valley) and Col Quaternà (western Comelico), respectively, probably represent a second pulse of andesite magmatic activity.Near Chiusa/Klausen, the volcanoclastic deposits at the bottom of the Funes/Villnöss valley volcano-sedimentary complex only contain detrital zircons, dated at 469 ± 6 Ma; these probably derive from erosion of Paleozoic porphyroids. Other zircons from the same sediments and inherited cores of magmatic andesite crystals give Paleoproterozoic (1953.6 ± 22.1, 1834.6 ± 69.3, 1773.6 ± 25.1 Ma), Early Neoproterozoic (1015 ± 14 Ma) and Late Neoproterozoic (728.4 ± 9.6, 687.6 ± 7.6 Ma) ages. These ancient detrital and inherited zircon ages fit the model that envisages the Dolomite region as being tectonically coherent with Africa, at least until the Lower Permian. 相似文献
50.
Summary A wide range of types of contact morphology among mafic and felsic magmas are observed in outcrops on Vegetation Island (Terra Nova Intrusive Complex, Antarctica). Image analysis and fractal geometry techniques were applied for in-depth study of the mafic/felsic interface, with the aim of studying the origin of the varied morphologies. In particular, the length (IPN) and fractal dimension (Dbox) of interfaces were measured. Results indicate that there is a close exponential dependence of IPN on Dbox.The observed morphologies are identical to those observed during viscous fingering processes induced by the displacement of a more viscous fluid by a less viscous one. To test if viscous fingering was responsible in this case too, IPN and Dbox values were measured on viscous fingering structures obtained experimentally using various viscosity ratios (VR) from the literature. Results indicate that, as in the natural case, there is an exponential dependence of IPN on Dbox, leading to the conclusion that the varied interface morphologies between mafic and felsic magmas are the result of viscous fingering dynamics. In addition, experimental studies clearly show that there is an exponential relationship between the viscosity ratio of fluids and the interface fractal dimension (Dbox), and the ratio between the two types of magma was estimated using this relationship. It is shown that viscosity contrasts between mafic and felsic magmas varied considerably, ratios ranging from ca. 6 to 49. These results, together with outcrop evidence, provide indications regarding the evolution of the magmatic system, which generated the actual mafic/felsic associations on Vegetation Island. 相似文献