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101.
This formulation of the free energy of mixing in a binary system takes as parameters a Bragg-Williams type cooperative disordering energy and the difference in free energy between different structures for the end-members. Subsolidus phase relations in carbonate systems such as CaCO3—MgCO3 and CdCO3—MgCO3 are calculated. Similar equations also reproduce the topologies of subsolidus phase relations in pyroxenes, including orthopyroxene-clinopyroxene phase boundaries in the enstatitediopside and ferrosilite-hedenbergite systems, the pigeonite-augite solvus, and the stability field of iron-free pigeonite. 相似文献
102.
Marine organic geochemistry of the Eastern Mediterranean: 1. Aliphatic and polyaromatic hydrocarbons in Cretan Sea surficial sediments 总被引:1,自引:0,他引:1
As part of a lipid biogeochemical study, aliphatic and polyaromatic hydrocarbons were determined in surficial sediments from the Cretan Sea (South Aegean Sea) in the Eastern Mediterranean. Total concentrations of both aliphatic (AHC) and polyaromatic (PAH) hydrocarbons were low (562–5697 and 14.6–158.5 ng/g, respectively) with respect to other coastal sediments worldwide and compare with concentrations found in open sea areas. The composition of AHC was dominated by unresolved complex mixture (UCM) indicating the presence of petroleum-related hydrocarbon inputs as confirmed by the detection of specific α,β-hopanes. PAH consisted mainly of pyrolytic four- to five-ring compounds. UCM and PAH amounts revealed that Cretan Sea receives low supply of anthropogenic material compared to NW Mediterranean. The spatial distributions of AHC and PAH indicated that urban run-off and transport from the continental self are the major input pathway of anthropogenic and biogenic hydrocarbons from terrestrial sources in the near shore area, whereas atmospheric transport might be the significant source of hydrocarbons in the deep area. 相似文献
103.
Characterization of mesostasis regions in lunar basalts: Understanding late‐stage melt evolution and its influence on apatite formation 下载免费PDF全文
Nicola J. Potts Romain Tartèse Mahesh Anand Wim van Westrenen Alexandra A. Griffiths Thomas J. Barrett Ian A. Franchi 《Meteoritics & planetary science》2016,51(9):1555-1575
Recent studies geared toward understanding the volatile abundances of the lunar interior have focused on the volatile‐bearing accessory mineral apatite. Translating measurements of volatile abundances in lunar apatite into the volatile inventory of the silicate melts from which they crystallized, and ultimately of the mantle source regions of lunar magmas, however, has proved more difficult than initially thought. In this contribution, we report a detailed characterization of mesostasis regions in four Apollo mare basalts (10044, 12064, 15058, and 70035) in order to ascertain the compositions of the melts from which apatite crystallized. The texture, modal mineralogy, and reconstructed bulk composition of these mesostasis regions vary greatly within and between samples. There is no clear relationship between bulk‐rock basaltic composition and that of bulk‐mesostasis regions, indicating that bulk‐rock composition may have little influence on mesostasis compositions. The development of individual melt pockets, combined with the occurrence of silicate liquid immiscibility, exerts greater control on the composition and texture of mesostasis regions. In general, the reconstructed late‐stage lunar melts have roughly andesitic to dacitic compositions with low alkali contents, displaying much higher SiO2 abundances than the bulk compositions of their host magmatic rocks. Relevant partition coefficients for apatite‐melt volatile partitioning under lunar conditions should, therefore, be derived from experiments conducted using intermediate compositions instead of compositions representing mare basalts. 相似文献
104.
Moving foreign human and financial capital through landed property is not a new phenomenon in Sydney. It is a recurring geopolitical strategy that is replete with intercultural tension and deep colonial roots. In contemporary Australia, there is an assumption in public policy and media rhetoric that there is a high level of public concern about foreign investment. However, there is little empirical data that examines public perceptions. In this study, we are interested in whether the dominant voices in this debate represent broad public views about this issue. We sought to fill this gap by conducting a survey of almost 900 Sydney residents, looking at their perceptions of foreign and Chinese investment. We find high levels of public concern and discontent about foreign investment amongst Sydneysiders, with Chinese investors being a key target of this discontent. In the context of high housing prices in Sydney, there were widely held concerns about housing affordability. Survey respondents had a sophisticated understanding of what influences house prices, but with an overemphasis on the role of foreign investment. There is a general lack of support for policy that encourages foreign investment, and a lack of confidence in how the government is regulating foreign investment. Half of our participants reported that they would not welcome Chinese foreign investment in their suburb. 相似文献
105.
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107.
Is Ocean Acidification an Open-Ocean Syndrome? Understanding Anthropogenic Impacts on Seawater pH 总被引:2,自引:0,他引:2
Carlos M. Duarte Iris E. Hendriks Tommy S. Moore Ylva S. Olsen Alexandra Steckbauer Laura Ramajo Jacob Carstensen Julie A. Trotter Malcolm McCulloch 《Estuaries and Coasts》2013,36(2):221-236
Ocean acidification due to anthropogenic CO2 emissions is a dominant driver of long-term changes in pH in the open ocean, raising concern for the future of calcifying organisms, many of which are present in coastal habitats. However, changes in pH in coastal ecosystems result from a multitude of drivers, including impacts from watershed processes, nutrient inputs, and changes in ecosystem structure and metabolism. Interaction between ocean acidification due to anthropogenic CO2 emissions and the dynamic regional to local drivers of coastal ecosystems have resulted in complex regulation of pH in coastal waters. Changes in the watershed can, for example, lead to changes in alkalinity and CO2 fluxes that, together with metabolic processes and oceanic dynamics, yield high-magnitude decadal changes of up to 0.5 units in coastal pH. Metabolism results in strong diel to seasonal fluctuations in pH, with characteristic ranges of 0.3 pH units, with metabolically intense habitats exceeding this range on a daily basis. The intense variability and multiple, complex controls on pH implies that the concept of ocean acidification due to anthropogenic CO2 emissions cannot be transposed to coastal ecosystems directly. Furthermore, in coastal ecosystems, the detection of trends towards acidification is not trivial and the attribution of these changes to anthropogenic CO2 emissions is even more problematic. Coastal ecosystems may show acidification or basification, depending on the balance between the invasion of coastal waters by anthropogenic CO2, watershed export of alkalinity, organic matter and CO2, and changes in the balance between primary production, respiration and calcification rates in response to changes in nutrient inputs and losses of ecosystem components. Hence, we contend that ocean acidification from anthropogenic CO2 is largely an open-ocean syndrome and that a concept of anthropogenic impacts on marine pH, which is applicable across the entire ocean, from coastal to open-ocean environments, provides a superior framework to consider the multiple components of the anthropogenic perturbation of marine pH trajectories. The concept of anthropogenic impacts on seawater pH acknowledges that a regional focus is necessary to predict future trajectories in the pH of coastal waters and points at opportunities to manage these trajectories locally to conserve coastal organisms vulnerable to ocean acidification. 相似文献
108.
Alexandra?L.?MitchellEmail author Timothy?L.?Grove 《Contributions to Mineralogy and Petrology》2016,171(12):107
This experimental study simulates the interaction of hotter, deeper hydrous mantle melts with shallower, cooler depleted mantle, a process that is expected to occur in the upper part of the mantle wedge. Hydrous reaction experiments (~6 wt% H2O in the melt) were conducted on three different ratios of a 1.6 GPa mantle melt and an overlying 1.2 GPa harzburgite from 1060 to 1260 °C. Reaction coefficients were calculated for each experiment to determine the effect of temperature and starting bulk composition on final melt compositions and crystallizing assemblages. The experiments used to construct the melt–wall rock model closely approached equilibrium and experienced <5% Fe loss or gain. Experiments that experienced higher extents of Fe loss were used to critically evaluate the practice of “correcting” for Fe loss by adding iron. At low ratios of melt/mantle (20:80 and 5:95), the crystallizing assemblages are dunites, harzburgites, and lherzolites (as a function of temperature). When the ratio of deeper melt to overlying mantle is 70:30, the crystallizing assemblage is a wehrlite. This shows that wehrlites, which are observed in ophiolites and mantle xenoliths, can be formed by large amounts of deeper melt fluxing though the mantle wedge during ascent. In all cases, orthopyroxene dissolves in the melt, and olivine crystallizes along with pyroxenes and spinel. The amount of reaction between deeper melts and overlying mantle, simulated here by the three starting compositions, imposes a strong influence on final melt compositions, particularly in terms of depletion. At the lowest melt/mantle ratios, the resulting melt is an extremely depleted Al-poor, high-Si andesite. As the fraction of melt to mantle increases, final melts resemble primitive basaltic andesites found in arcs globally. An important element ratio in mantle lherzolite composition, the Ca/Al ratio, can be significantly elevated through shallow mantle melt–wall rock reaction. Wall rock temperature is a key variable; over a span of <80 °C, reaction with deeper melt creates the entire range of mantle lithologies from a depleted dunite to a harzburgite to a refertilized lherzolite. Together, the experimental phase equilibria, melt compositions, and reaction coefficients provide a framework for understanding how melt–wall rock reaction occurs in the natural system during melt ascent in the mantle wedge. 相似文献
109.
An Upper Maastrichtian horizon rich in Loftusia is for the first time described in situ in Greece in the province of Boeotia. It is found in a continuous undisturbed carbonate sequence of the eastern Greece platform (Subpelagonian zone) of Maastrichtian–Paleocene age followed by flysch sedimentation. Loftusia is found in a facies reflecting an outer shelf environment, associated with debris of rudists, Orbitoides spp., Siderolites calcitrapoides, Omphalocyclus macroporus, Hellenocyclina beotica, Sulcoperculina sp., and echinoderms. Similar fauna, but without Loftusia, is found in the surrounding levels of Late Maastrichtian age as well. This recovery of the genus in the western part of its distribution area, where it is not as abundant as in the eastern part, is considered significant for the palaeobiogeography of the genus in Tethys Ocean during Late Cretaceous. To cite this article: A. Zambetakis-Lekkas, A. Kemeridou, C. R. Geoscience 338 (2006). 相似文献
110.
Brian L. Phillips Pamela C. Burnley Karen Worminghaus Alexandra Navrotsky 《Physics and Chemistry of Minerals》1997,24(3):179-190
We present NMR spectroscopic data, obtained by 1H MAS, 1H static spin-echo, and 29Si{1H} CP-MAS techniques, for a series of hydrous magnesium silicate samples synthesized at high pressure. This series includes chondrodite, β-Mg2SiO4, and phases A, B, superhydrous B, and E. Phases B and superhydrous B give very narrow 29Si NMR peaks and display the most de-shielded SiVI chemical shifts yet reported: ?170.4?ppm for B and ?166.6 for superhydrous B. The 1H NMR spectra of B and superhydrous B confirm the presence of paired hydroxyls, as determined from refinement of the H positions from X-ray diffraction data. The 1H MAS NMR spectra of phase B contain peaks for the two distinct hydrogen positions, with chemical shifts of +4.7 and +3.3?ppm. The static 1H spectrum contains a powder pattern characteristic of a strongly coupled hydrogen pair, from which a dipolar coupling constant of 18.6(4)?kHz and inter-hydrogen distance of d(H–H)=1.86(2)?Å were obtained. Superhydrous B appears to give two poorly resolved 1H MAS peaks, consistent with the presence of two distinct hydrogen pairs in the P21 mn crystal structure. Analysis of its spin-echo spectrum gives d(H–H)=1.83(3)?Å, slightly shorter than for phase B. β-Mg2SiO4, coexisting with phases B and superhydrous B, appears to give 29Si{1H} CP-MAS signal, indicating that it contains significant H concentration. The 29Si chemical shifts for phases B, superhydrous B, and chondrodite, together with those reported previously for other Mg-silicates, show a good correlation with structural parameters. 相似文献