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101.
The Xinjie layered intrusion in the Panxi region,SW China,hosts both Fe-Ti oxide and platinum-group element(PGE) sulfide mineralization.The intrusion can be divided,from the base upward,into UnitsⅠ,ⅡandⅢ,in terms of mineral assemblages.UnitsⅠandⅡare mainly composed of wehrlite and clino-pyroxenite, whereas UnitⅢis mainly composed of gabbro.PGE sulfide-rich layers mainly occur in Unit I, whereas thick Fe-Ti oxide-rich layers mainly occur in UnitⅢ.An ilmenite-rich layer occurs at the top of UnitⅠ.Fe-Ti oxides include magnetite and ilmenite.Small amounts of cumulus and intercumulus magnetite occur in UnitsⅠandⅡ.Cumulus magnetite grains are commonly euhedral and enclosed within olivine and clinopyroxene.They have high Cr2O3 contents ranging from 6.02 to 22.5 wt.%,indicating that they are likely an early crystallized phase from magmas.Intercumulus magnetite that usually displays ilmenite exsolution occupies the interstices between cumulus olivine crystals and coexists with interstitial clinopyroxene and plagioclase.Intercumulus magnetite has Cr2O3 ranging from 1.65 to 6.18 wt.%, lower than cumulus magnetite.The intercumulus magnetite may have crystallized from the trapped liquid.Large amounts of magnetite in UnitⅢcontains Cr2O3(<0.28 wt.%) much lower than magnetite in UnitsⅠandⅡ.The magnetite in UnitⅢis proposed to be accumulated from a Fe-Ti-rich melt.The Fe-Ti-rich melt is estimated to contain 35.9 wt.%of SiO2,26.9 wt.%of FeOt,8.2 wt.%of TiO2,13.2 wt.%of CaO, 8.3 wt.%of MgO,5.5 wt.%of Al2O3 and 1.0 wt.%of P2O5.The composition is comparable with the Fe-rich melts in the Skaergaard and Sept Iles intrusions.Paired non-reactive microstructures,granophyre pockets and ilmenite-rich intergrowths,are representative of Si-rich melt and Fe-Ti-rich melt,and are the direct evidence for the existence of an immiscible Fe-Ti-rich melt that formed from an evolved ferro-basaltic magma. 相似文献
102.
David J. Lawrence John K. Harmon William C. Feldman John O. Goldsten David A. Paige Patrick N. Peplowski Edgar A. Rhodes Christina M. Selby Sean C. Solomon 《Planetary and Space Science》2011,59(13):1665-1669
From radar images of Mercury's poles and MESSENGER Neutron Spectrometer (NS) measurements obtained during the spacecraft's flybys of Mercury, predictions of neutron count rates and their uncertainties are calculated for Mercury's north polar region as of the end of the MESSENGER primary orbital mission. If Mercury's poles contain large amounts of water ice, as has been suggested on the basis of the radar data, then during the one-year-long orbital mission the NS should detect signals indicative of excess polar hydrogen with a significance of at least 4σ, where σ is the standard deviation derived from Poisson counting statistics. If the polar deposits are not enriched with hydrogen, but are dominated by other elements, such as sulfur, then the MESSENGER neutron measurements should be able to confirm the absence of deposits having surface concentrations in excess of 50 wt% H2O on permanently shadowed floors of craters near Mercury's north pole. Because of the large spatial footprint of the NS data, individual polar deposits will not be spatially resolved, but longitudinal asymmetries may be detected if residual systematic uncertainties are sufficiently low. 相似文献
103.
Anna Milillo Valeria Mangano Alessandro Mura Stefano Orsini Elisabetta De Angelis Andrea M. Di Lellis Stefano Massetti Christina Plainaki Rosanna Rispoli Stefano Selci Nello Vertolli 《Experimental Astronomy》2011,32(1):37-49
Observation of the lunar exosphere is a tool for remote sensing of the surface properties. The sources of this exosphere are related to the interactions of the lunar surface with the solar radiation, with the solar wind or Earth??s magnetospheric plasma, and with the interplanetary dust and meteorites. In fact, the exospheric particles are continuously created and subsequently lost in the interplanetary space, photo-ionized or re-adsorbed by the surface. Eventually, the estimation of the surface composition is not possible without the knowledge of the active release mechanisms. The relative weight of the different release processes of the various atoms, ions and molecules from the surface is still an open debate. Investigation of the Moon??s release processes and interaction with the near-Earth environment is of crucial importance for both determining the relative process release contribution and understanding the surface evolution of other airless bodies, like Mercury and the giant planets?? moons. In this work, an attempt to analyze the processes that take place on the surface of these small airless bodies, as a result of their exposure to the space environment, has been realized by means of the MonteCarlo Environment Simulation Tool (EST), applied to the Moon. The model results show that the different release processes can be identified by analysing the exospheric energy distribution. Finally, the instrument concept of the ??Analizzatore Lunare di ENA?? (ALENA), part of the MAGIA payload and specifically designed for detecting the high-energy particles released from the lunar surface is presented. 相似文献
104.
105.
Christina Simkanin Ian C. Davidson John F. Dower Glen Jamieson Thomas W. Therriault 《Marine Ecology》2012,33(4):499-511
Anthropogenic habitats such as marinas and docks are focal points for marine invasions, but relatively little is known about the infiltration of nearby natural habitats by these invaders. To address infiltration by four geographically widespread ascidian invaders, we used a two‐step approach: (i) a field survey with equitable sampling in adjacent artificial and natural habitats in British Columbia, Canada, and (ii) a literature review, to infer larger scale patterns across species’ introduced global ranges. Our field survey revealed differential distribution patterns among the four ascidians recorded, with infiltration of natural rocky habitats by two species, Botrylloides violaceus and Botryllus schlosseri. We did not record Didemnum vexillum or Styela clava in natural habitats, though they were both recorded on adjacent artificial structures. Globally, these ascidian species are predominantly found associated with anthropogenic habitats including floating docks, pilings and aquaculture installations, but they have infiltrated natural habitats in some areas of their introduced range. The factors contributing to infiltration of nearby natural benthic habitats remains unclear, but determining which mechanisms are important for encouraging or hindering the establishment and spread of nonindigenous species beyond artificial structures requires survey and experimental work beyond anthropogenic habitats. Such work will aid our understanding of marine introduction dynamics, invasiveness, and associated management implications. 相似文献
106.
Christina Anagnostopoulou Konstantia Tolika 《Theoretical and Applied Climatology》2012,107(3-4):479-489
In the present study, both parametric (peak over threshold: mean residual life, dispersion index, threshold choice) and non-parametric (percentiles indices 95% and 99%) statistical techniques are employed, aiming at the identification of rainfall thresholds above which a precipitation event can be characterized as extreme. The analysis is based on 45?years (1960–2004) rain gauge daily records from 65 meteorological stations over the European region. According to two climatologically based criteria that were introduced in the study, it was found that a combined peak over threshold methodology has been shown to yield higher threshold values above which extreme precipitation events occur, in comparison to the 95th percentile indices. Overall, concerning northern Europe, it was found that in the majority of the stations, the threshold values vary from 20 to 30?mm, while the results concerning the Mediterranean region are less coherent and the selection of extreme precipitation thresholds differs from region to region. Stations over eastern Mediterranean appear to have thresholds higher than 30?mm, while stations located over the main cyclone trajectories and the cyclogenesis zone of Mediterranean are those with the higher extreme precipitation thresholds (higher than 45?mm). 相似文献
107.
Water security: Debating an emerging paradigm 总被引:2,自引:0,他引:2
This paper presents a comprehensive review of the concept of water security, including both academic and policy literatures. The analysis indicates that the use of the term water security has increased significantly in the past decade, across multiple disciplines. The paper presents a comparison of definitions of, and analytical approaches to, water security across the natural and social sciences, which indicates that distinct, and at times incommensurable, methods and scales of analysis are being used. We consider the advantages and disadvantages of narrow versus broad and integrative framings of water security, and explore their utility with reference to integrated water resources management. In conclusion, we argue that an integrative approach to water security brings issues of good governance to the fore, and thus holds promise as a new approach to water management. 相似文献
108.
Christina Schornberg Christian Schmidt Edda Kalbus Jan H. Fleckenstein 《Advances in water resources》2010
Analytical solutions to the one-dimensional heat transport equation for steady-state conditions can provide simple means to quantify groundwater surface water exchange. The errors in exchange flux calculations that are introduced when the underlying assumptions of homogeneous sediments and constant temperature boundary conditions are violated were systematically evaluated in a simulation study. Temperatures in heterogeneous sediments were simulated using a numerical model. Heterogeneity in the sediments was represented by discrete, binary geologic units. High contrasts between the hydraulic conductivities (K) of the geologic units were found to lead to large errors, while the influence of the structural arrangement of the units was smaller. The effects of transient temperature boundary conditions were investigated using an analytical equation. Errors introduced by transient boundary conditions were small for Darcy-velocities > 0.1 m d− 1 in the period near maximum and minimum annual surface water temperatures. For smaller fluxes, however, errors can be large. Assuming steady-state conditions and vertical flow in homogeneous sediments is acceptable at certain times of the year and for medium to high exchange fluxes, but pronounced geologic heterogeneity can lead to large errors. 相似文献
109.
Arsenic concentrations can be managed with a relatively simple strategy of grouting instead of completely destroying a selected interval of well. The strategy of selective grouting was investigated in Antelope Valley, California, where groundwater supplies most of the water demand. Naturally occurring arsenic typically exceeds concentrations of 10 µg/L in the water produced from these long-screened wells. The vertical distributions of arsenic concentrations in intervals of the aquifer contributing water to selected supply wells were characterized with depth-dependent water-quality sampling and flow logs. Arsenic primarily entered the lower half of the wells where lacustrine clay deposits and a deeper aquifer occurred. Five wells were modified by grouting from below the top of the lacustrine clay deposits to the bottom of the well, which reduced produced arsenic concentrations to less than 2 µg/L in four of the five wells. Long-term viability of well modification and reduction of specific capacity was assessed for well 4-54 with AnalyzeHOLE, which creates and uses axisymmetric, radial MODFLOW models. Two radial models were calibrated to observed borehole flows, drawdowns, and transmissivity by estimating hydraulic-conductivity values in the aquifer system and gravel packs of the original and modified wells. Lithology also constrained hydraulic-conductivity estimates as regularization observations. Well encrustations caused as much as 2 µg/L increase in simulated arsenic concentration by reducing the contribution of flow from the aquifer system above the lacustrine clay deposits. Simulated arsenic concentrations in the modified well remained less than 3 µg/L over a 20-year period. 相似文献
110.
Ute Christina Herzfeld 《Mathematical Geology》1993,25(7):901-924
Seafloor classification is aimed at quantitatively characterizing seafloor properties such as roughness and anisotropy, and at using such spatial characteristics to distinguish geological provinces automatically. From geostatistical principals, a variogram method is developed for seafloor classification and it is demonstrated for data from the western flank of the Mid-Atlantic Ridge at 25°45N to 26°40N. This study uses HYDROSWEEP bathymetric data which have been ping-edited to flag erroneous data records, and navigation corrected. The classification method can handle the resultant data gaps inside the survey swaths as well as interpret data from several swaths. For a suite of test areas representative of different geological provinces, directional variograms are calculated, and characteristic parameters are extracted for the classification. Examples include a sediment pond, abyssal hill terrain in several segments and of variable spacing, inside and outside corners of ridge discontinuities, and mixed morphological forms. The dependency of the results on random or regular subsampling and on the size of the test area is investigated. 相似文献