H,not O or pressure,causes eutectic T depression in the Fe‐FeS System to 8 GPa          下载免费PDF全文

Antonio S. Buono  David Walker 《Meteoritics & planetary science》2015,50(4):547-554

The Fe‐FeS system maintains a eutectic temperature of 990 ± 10 °C to at least 8 GPa if starting materials and pressure media are rigorously dehydrated. Literature reports of pressure‐induced freezing point depression of the eutectic for the Fe‐FeS system are not confirmed. Modest addition of oxygen alone is confirmed to cause negligible freezing point depression at 6 GPa. Addition of H alone causes a progressive decrease in the eutectic temperature with P in the Fe‐FeS‐H system to below 965 °C at 6 GPa to below 950 °C at 8 GPa. It is our hypothesis that moisture contamination in unrigorously dried experiments may be an H source for freezing point depression. O released from H₂O disproportionation reacts with Fe and is sequestered as ferropericlase along the sample capsules walls, leaving the H to escape the system and/or enter the Fe‐FeS mixture. The observed occurrence of ferropericlase on undried MgO capsule margins is otherwise difficult to explain, because an alternate source for the oxygen in the ferropericlase layer is difficult to identify. This study questions the use of pressure‐depressed Fe‐S eutectic temperatures and suggests that the lower eutectic temperatures sometimes reported are achieved by moving into the ternary Fe‐S‐H system. These results adjust slightly the constraints on eutectic temperatures allowed for partly solidified cores on small planets. H substantially diminishes the temperature extent of the melting interval in Fe‐S by reducing the melting points of the crystalline phases more than it depresses the eutectic.  相似文献   

A Galileo IOV assessment: measurement and position domain     

Ciro Gioia  Daniele Borio  Antonio Angrisano  Salvatore Gaglione  Joaquim Fortuny-Guasch 《GPS Solutions》2015,19(2):187-199

  相似文献   

Geochronological study of zircons from continental crust rocks in the Frido Unit (southern Apennines)     

Salvatore Laurita  Giacomo Prosser  Giovanna Rizzo  Antonio Langone  Massimo Tiepolo  Alessandro Laurita 《International Journal of Earth Sciences》2015,104(1):179-203

  相似文献   

Karst massif susceptibility from rock matrix,fracture and conduit porosities: a case study of the Sierra de las Nieves (Málaga,Spain)     

Eulogio Pardo-Igúzquiza  Juan José Durán  Juan A. Luque-Espinar  Pedro A. Robledo-Ardila  Sergio Martos-Rosillo  Carolina Guardiola-Albert  Antonio Pedrera 《Environmental Earth Sciences》2015,74(12):7583-7592

  相似文献   

The Fe-rich liquidus in the Fe-FeS system from 1 bar to 10 GPa     

Antonio S. Buono  David Walker 《Geochimica et cosmochimica acta》2011,75(8):2072-2087

The composition and evolution of a metallic planetary core is determined by the behavior with pressure of the eutectic and the liquidus on the Fe-rich side of the Fe-FeS eutectic. New experiments at 6 GPa presented here, along with existing experimental data, inform a thermodynamic model for this liquidus from 1 bar to at least 10 GPa. Fe-FeS has a eutectic that becomes more Fe-rich but remains constant in T up to 6 GPa. The 1 bar, 3 GPa, and 6 GPa liquidi all cross at a pivot point at 1640 ± 5 K and FeS_37 ± 0.5. This liquid/crystalline metal equilibrium is T-x-fixed and pressure independent through 6 GPa. Models of the 1 bar through 10 GPa experimental liquidi show that with increasing P there is an increase in the T separation between the liquidus and the crest of the metastable two-liquid solvus. The solvus crest decreases in T with increasing P. The model accurately reproduces all the experimental liquidi from 1 bar to 10 GPa, as well as reproducing the 0-6 GPa pivot point. The 14 GPa experimental liquidus ( [Chen et al., 2008a] and Chen et al., 2008b) deviates sharply from the lower pressure trends indicating that the 0-10 GPa model no longer applies to this 14 GPa data.  相似文献   

Solute transport scales in an unsaturated stony soil     

Antonio Coppola  Alessandro ComegnaGiovanna Dragonetti  Miles DyckAngelo Basile  Nicola LamaddalenaMohamed Kassab  Vincenzo Comegna 《Advances in water resources》2011,34(6):747-759

Solute transport parameters are known to be scale-dependent due mainly to the increasing scale of heterogeneities with transport distance and with the lateral extent of the transport field examined. Based on a transect solute transport experiment, in this paper we studied this scale dependence by distinguishing three different scales with different homogeneity degrees of the porous medium: the observation scale, transport scale and transect scale. The main objective was to extend the approach proposed by van Wesenbeeck and Kachanoski to evaluating the role of textural heterogeneities on the transition from the observation scale to the transport scale. The approach is based on the scale dependence of transport moments estimated from solute concentrations distributions. In our study, these moments were calculated starting from time normalized resident concentrations measured by time domain reflectometry (TDR) probes at three depths in 37 soil sites 1 m apart along a transect during a steady state transport experiment. The Generalized Transfer Function (GTF) was used to describe the evolution of apparent solute spreading along the soil profile at each observation site by analyzing the propagation of the moments of the concentration distributions. Spectral analysis was used to quantify the relationship between the solid phase heterogeneities (namely, texture and stones) and the scale dependence of the solute transport parameters. Coupling the two approaches allowed us to identify two different transport scales (around 4-5 m and 20 m, respectively) mainly induced by the spatial pattern of soil textural properties. The analysis showed that the larger transport scale is mainly determined by the skeleton pattern of variability. Our analysis showed that the organization in hierarchical levels of soil variability may have major effects on the differences between solute transport behavior at transport scale and transect scale, as the transect scale parameters will include information from different scales of heterogeneities.  相似文献   

Diurnal-inertial motions and diapycnal mixing on the Portuguese shelf     

Borja Aguiar-González  Ángel Rodríguez-Santana Jesús Cisneros-Aguirre  Antonio Martínez-Marrero 《Continental Shelf Research》2011,31(11):1193-1201

  相似文献   

Estimating quality factor from surface seismic data: A comparison of current approaches     

Bonnie Ives de Castro Nunes  Walter Eugênio de Medeiros  Aderson Farias do Nascimento  José Antonio de Morais Moreira 《Journal of Applied Geophysics》2011,75(2):161-170

The performances of the spectral ratio (SR), frequency centroid shift (FCS), and frequency peak shift (FPS) methods to estimate the effective quality factor Q are compared. These methods do not demand true amplitude data and their implementations were done following an “as simple as possible” approach to highlight their intrinsic potentials and limitations. We use synthetic zero-offset seismic data generated with a simple layer-cake isotropic model. The methods can be ranked from simple to complex in terms of automation as: FPS, FCS and SR. This is a consequence of: (i) peak identification consists basically of a sorting procedure, (ii) centroid estimation involves basically the evaluation of two well-behaved integrals, and (iii) implementation of the SR method involves at least choosing a usable frequency bandwidth and fitting a gradient. The methods can be ranked from robust to sensitive in the presence of noise content in the sequence SR, FCS, and FPS. This is consequence of: (i) the gradient estimate associated to the SR method averages out the noise content in the entire usable frequency bandwidth, (ii) in the presence of moderate-to-high noise level, the centroid estimation is biassed towards overestimating Q due to noise contribution in the tail of the amplitude spectrum, and (iii) peak identification is unstable due to local noise fluctuation in the amplitude spectrum around the peak frequency. Regarding the stability of the estimates relative to the attenuation amount, SR and FCS methods show similar behaviours, whereas FPS method presents an inferior performance. This fact is an indirect consequence of the sensitivity of FPS method to the noise content because the higher is the attenuation the lower is the signal-to-noise ratio. Finally, regarding the robustness of the methods to the presence of dipping layers, only SR and FCS methods provide good estimates, at least to typical dips in non-faulted sedimentary layers, with the estimates obtained with SR method being more accurate that those obtained with FCS method. Except in relation to the automation complexity, which is less important than the performances of the methods, SR method was superior or showed similar performance to FCS method in all scenarios we tried.  相似文献   

Pelagic primary production in the Algero-Provençal Basin by means of multisensor satellite data: focus on interannual variability and its drivers     

Antonio Olita  Roberto Sorgente  Alberto Ribotti  Leopoldo Fazioli  Angelo Perilli 《Ocean Dynamics》2011,61(7):1005-1016

In this work, we make use of satellite estimates of chlorophyll a, photosynthetically active radiation and sea surface temperatures, to compute regional estimates of primary production integrated throughout the euphotic layer for the Algero-Provençal Basin, by means of a modified version of the vertically generalized production model. The seasonal and interannual variability of the primary production has been analysed over the decade 1997–2007. Empirical orthogonal functions analysis has been applied to decompose the variability of the primary production dataset in orthogonal modes of variability. The seasonal signal is distributed between the two first modes of variability, temporally shifted each other and respectively related to the northern (early spring) and the southern (winter) part of the basin. We found a minimum of the annual production in 2003, when a summer heatwave strongly enhanced the stratification of surface waters, further limiting the injection of nutrients into the surface layers. Maxima in the annual series are found in 1999 and 2005, due to two particularly intense and extended (in space) spring-blooms in the northern part of the basin. These two maxima, clearly identified in space and time by EOF analysis (EOF1 and EOF3), are related to strong mistral-wind interannual events occurring during winters of 1999 and 2005, preceding the blooms by some few months. We found that these production maxima are due both to a more intense production in the usual blooming area (shown by EOF1–PC1) as well as to an exceptional local production in the eastern side of the basin, off the Corsica western coasts (EOF3–PC3). Previous observations of exceptional deep-water formation events in 1999 and 2005, with easterly spots close to the primary production-observed anomalies, and the meridional character of the mistral 1999 and 2005 peaks both support the idea that such eastern PP interannual maxima would be actually due to exceptional production more than to an easterly advection of biomass from the usual bloom area. Finally, the potential link of the observed features with large-scale atmospheric forcing is discussed, and a potential relation of such interannual events with the East Atlantic pattern is drawn.  相似文献   

Pleistocene–Holocene environmental change in the Canary Archipelago as inferred from the stable isotope composition of land snail shells     

Yurena Yanes  Crayton J. Yapp  Miguel Ibez  María R. Alonso  Julio De-la-Nuez  María L. Quesada  Carolina Castillo  Antonio Delgado 《Quaternary Research》2011,75(3):658-669

The isotopic composition of land snail shells was analyzed to investigate environmental changes in the eastern Canary Islands (28–29°N) over the last ~ 50 ka. Shell δ¹³C values range from −8.9‰ to 3.8‰. At various times during the glacial interval (~ 15 to ~ 50 ka), moving average shell δ¹³C values were 3‰ higher than today, suggesting a larger proportion of C₄ plants at those periods. Shell δ¹⁸O values range from −1.9‰ to 4.5‰, with moving average δ¹⁸O values exhibiting a noisy but long-term increase from 0.1‰ at ~ 50 ka to 1.6–1.8‰ during the LGM (~ 15–22 ka). Subsequently, the moving average δ¹⁸O values range from 0.0‰ at ~ 12 ka to 0.9‰ at present. Calculations using a published snail flux balance model for δ¹⁸O, constrained by regional temperatures and ocean δ¹⁸O values, suggest that relative humidity at the times of snail activity fluctuated but exhibited a long-term decline over the last ~ 50 ka, eventually resulting in the current semiarid conditions of the eastern Canary Islands (consistent with the aridification process in the nearby Sahara). Thus, low-latitude oceanic island land snail shells may be isotopic archives of glacial to interglacial and tropical/subtropical environmental change.  相似文献