Fractionation vs. magma mixing in the Wangrah Suite A-type granites, Lachlan Fold Belt, Australia: Experimental constraints   总被引：1，自引：0，他引：1  

Kevin Klimm  Francois Holtz  Penelope L. King 《Lithos》2008,102(3-4):415-434

The Wangrah Suite granites (Lachlan Fold Belt, Australia) reflect different stages of differentiation in the magmatic history of an A-type plutonic suite. In this study we use experimentally determined phase equilibria of four natural A-type granitic compositions of the Wangrah Suite to constrain phases and phase compositions involved in fractionation processes. Each composition represents a distinct granite intrusion in the Wangrah Suite. The intrusions are the Danswell Creek (DCG), Wangrah (WG), Eastwood (EG) and Dunskeig Granite (DG), ordered from “most mafic” to “most felsic” by increasing SiO₂ and decreasing FeO_total.

Experimental investigation show that the initial water content in melts from DCG is between 2–3 wt. % H₂O. If the DCG is viewed as the parental magma for the Wangrah Suite, then (1) fractionation of magnetite, orthopyroxene and plagioclase ( 20 wt. %) of the DCG composition, leads to compositions similar to that of the EG; (2) further fractionation of plagioclase, quartz, K-feldspar and biotite ( 40 wt. %) from the EG composition, leads to the DG composition. These fractionation steps can occur nearly isobarically and are confirmed by bulk rock Ba, Sr, Rb and Zr concentrations.

In contrast, the generation of the most abundant WG composition cannot be explained by fractional crystallisation from the DCG at isobaric conditions because of the high K₂O content of this granite. Magma Mixing could be the process to explain the chemical distinctiveness of the Wangrah Granite from all the other granites of the Wangrah Suite.  相似文献   

Assessment of Planetary-Boundary-Layer Schemes in the Weather Research and Forecasting Model Within and Above an Urban Canopy Layer     

Enrico Ferrero  Stefano Alessandrini  Francois Vandenberghe 《Boundary-Layer Meteorology》2018,168(2):289-319

We tested several planetary-boundary-layer (PBL) schemes available in the Weather Research and Forecasting (WRF) model against measured wind speed and direction, temperature and turbulent kinetic energy (TKE) at three levels (5, 9, 25 m). The Urban Turbulence Project dataset, gathered from the outskirts of Turin, Italy and used for the comparison, provides measurements made by sonic anemometers for more than 1 year. In contrast to other similar studies, which have mainly focused on short-time periods, we considered 2 months of measurements (January and July) representing both the seasonal and the daily variabilities. To understand how the WRF-model PBL schemes perform in an urban environment, often characterized by low wind-speed conditions, we first compared six PBL schemes against observations taken by the highest anemometer located in the inertial sub-layer. The availability of the TKE measurements allows us to directly evaluate the performances of the model; results of the model evaluation are presented in terms of quantile versus quantile plots and statistical indices. Secondly, we considered WRF-model PBL schemes that can be coupled to the urban-surface exchange parametrizations and compared the simulation results with measurements from the two lower anemometers located inside the canopy layer. We find that the PBL schemes accounting for TKE are more accurate and the model representation of the roughness sub-layer improves when the urban model is coupled to each PBL scheme.  相似文献   

华北地台西缘晚石炭世-早二叠世早期海水进退及其与聚煤作用的关系   总被引：11，自引：2，他引：9       下载免费PDF全文

彭格林  钟蓉  唐伟忠 《古地理学报》1999,1(2):18-27

从古元古代至晚古生代,华北地台西缘经历了坳拉槽、槽后坳和坳陷发育阶段。笔者在大区域地层对比及详细的沉积环境分析基础上,对晚古生代海水进退与聚煤作用关系作了较深入研究。结果表明：晚石炭世晚期至早二叠世早期华北地台西缘主要为潮坪和三角洲沉积发育区,在空间上沉积环境具有东西有别南北分带的特点;西部由泻湖潮坪沉积环境逐渐过渡为河控泻湖三角洲和受潮汐影响的河控滨海三角洲沉积环境;东部为潮坪沉积环境,东侧边缘还出现近山滨海平原沉积环境。研究区在晚石炭世早期-早二叠世早期发生过4次2级海水进退,其中第三、第四次海侵全区发育。早二叠世早期初的第三次2级海侵是最大的一次。最大海侵前夕晚石炭世晚期末是大区域发育厚-巨厚煤层的最好时期。泻湖三角洲平原和陆源碎屑潮上泥炭坪及泥炭沼泽是最佳的聚煤场所。  相似文献   

Eight new δ Scuti stars     

Chris Koen  Ruby Van Rooyen  Francois Van Wyk  Freddy Marang 《Monthly notices of the Royal Astronomical Society》1999,309(4):1051-1062

HD 23194, a member of the Pleiades, was found to pulsate with a period of about 30 min. The literature on the star is reviewed, and it is concluded that it may be a marginal Am star in a binary system. HD 95321 is an evolved Am ( ρ Puppis) star with a 5.1-h periodicity. Mode identification of its pulsation, based on multicolour photometry, suggests that the oscillation is probably non-radial with ℓ=2. We also report on the discovery of six other new δ Scuti stars, some of which may be pulsating in gravity modes.  相似文献   

物化探方法对古墓完整性的研究   总被引：3，自引：1，他引：2  

彭格林  杨宗仁  佘仁富  程真 《物探与化探》2000,24(3):233-240

根据湖南春秋战国—秦汉古墓葬地质条件、埋葬特征与周边环境,遵循准确、简便、快捷和经济的原则,选择并运用放射性氡测量、汞测量和探地雷达等方法,对湘西北某县AB战国楚墓群4个大中型古墓和长沙杨家山古墓开展物化探综合勘查试验,取得了古墓完整性勘查研究的初步成功。  相似文献   

Mercury exosphere I. Global circulation model of its sodium component     

Francois Leblanc  R.E. Johnson 《Icarus》2010,209(2):280-300

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Sublimation of the Martian CO₂ Seasonal South Polar Cap     

Frédéric Schmidt  Bernard Schmitt  Francois Forget  Patrick Martin  Jean-Pierre Bibring  the OMEGA Team 《Planetary and Space Science》2010,58(10):1129-1138

The polar condensation/sublimation of CO₂, that involve about one fourth of the atmosphere mass, is the major Martian climatic cycle. Early observations in visible and thermal infrared have shown that the sublimation of the Seasonal South Polar Cap (SSPC) is not symmetric around the geographic South Pole.Here we use observations by OMEGA/Mars Express in the near-infrared to detect unambiguously the presence of CO₂ at the surface, and to estimate albedo. Second, we estimate the sublimation of CO₂ released in the atmosphere and show that there is a two-step process. From Ls=180° to 220°, the sublimation is nearly symmetric with a slight advantage for the cryptic region. After Ls=220° the anti-cryptic region sublimation is stronger. Those two phases are not balanced such that there is 22% ± 9 more mass the anti-cryptic region, arguing for more snow precipitation. We compare those results with the MOLA height measurements. Finally we discuss implications for the Martian atmosphere about general circulation and gas tracers, e.g. Ar.  相似文献   

Accumulation and transport behaviour of 241americium, 60cobalt and 134cesium by eggs of the spotted dogfish Scyliorhinus canicula     

Jeffree RA  Oberhansli F  Teyssie JL 《Marine pollution bulletin》2007,54(7):912-920

An experimental study examined the 96-h net influx from seawater of the anthropogenic radionuclides (241)Am, (60)Co and (134)Cs through the egg-case of the spotted dogfish Scyliorhinus canicula. Net influx directly through the wall of the egg-case was greatest for (134)Cs, then (241)Am and lastly (60)Co. Within the egg-case wall itself the measured concentration factors (CFs) and their gradients in the external, median and internal layers showed that for both (241)Am and (60)Co they were >10(3) in the external layer and declined by an order of magnitude in the interior layer. In contrast (134)Cs had a CF of only about three in the external layer which declined by a factor of 2 towards the two more internal layers of the egg-case. The egg-case apertures, that open within the prehatching stage of embryological development, significantly (P<0.05) increased the net influx of (241)Am and (60)Co to the interior of the egg-case, although their water concentrations were still lower than those in the labelled seawater bath. In contrast, the aperture did not increase the net influx of (134)Cs whose water concentrations equilibrated with those in seawater. Together these results indicate that the egg-case wall is very permeable to (134)Cs, representing little barrier to its movement, and hence consistent with the lack of importance of the aperture in determining its internal water concentrations in the egg-case. In contrast, (241)Am and (60)Co show much higher rates of accumulation by the egg-case, consistent with the measured reduced permeability of its wall, and therefore giving greater prominence to its aperture in the net transfer of these two radionuclides to the egg case's interior. The presence of the embryo within its egg-case did not significantly (P>0.05) affect the rates of influx of radioisotopes, with the exception of an interactive effect for (60)Co with the egg-case aperture (P<0.05). The CF of only (241)Am in the embryo itself relative to the external seawater concentration was significantly (P<0.05) enhanced by the presence of the aperture.  相似文献   

Detailed seismic stratigraphy of Lago Puyehue: implications for the mode and timing of glacier retreat in the Chilean Lake District     

Katrien Heirman  Marc De Batist  Francois Charlet  Jasper Moernaut  Emmanuel Chapron  Robert Brümmer  Mario Pino  Roberto Urrutia 《第四纪科学杂志》2011,26(7):665-674

Lago Puyehue is a glacigenic lake in the Chilean Lake District (40°S) with a complex deglaciation history. A detailed seismic–stratigraphic study of its sedimentary infill indicates a much earlier retreat of the glacier from the Lago Puyehue basin than the neighbouring glacier from the Lago Rupanco basin. Because of their close proximity, Rupanco meltwater streams played an important part in the depositional processes of Lago Puyehue. A timing discrepancy between the in‐lake ages of a sediment core and the outer‐lake ages of moraine deposits (re)opens the discussion on the timing of deglaciation in the Southern Hemisphere. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Late Holocene high precipitation events recorded in lake sediments and catchment geomorphology,Lake Vuoksjávrátje,NW Sweden          下载免费PDF全文

Annika Berntsson  Krister N. Jansson  Malin E. Kylander  Francois De Vleeschouwer  Sebastien Bertrand 《Boreas: An International Journal of Quaternary Research》2015,44(4):676-692

In this paper, we show the potential of combining multi‐proxy analysis of lake sediments with catchment geomorphology to better understand palaeoenvironmental changes. Previous studies have suggested that alpine lakes in N Sweden may be highly sensitive to variations in catchment erosion and precipitation, and that this sensitivity may influence ecologically based reconstructions of past temperature changes. We analysed lake sediments covering the last 5100 years from the alpine Lake Vuoksjávrátje in NW Sweden in order to identify different erosional regimes in the lake catchment, sediment sources and lake sedimentary processes, which ultimately affect the palaeoecological record. The measured proxies include elemental geochemistry from XRF core scanning, grain size, sediment accumulation rates, fraction of terrestrial organic carbon and geomorphological mapping, supported by previously published chironomid and total organic carbon data. From the integrated results we identified time intervals when increased intensity of precipitation altered sedimentation and lake catchment erosional processes. The most prominent event occurred c. 2900 cal. a BP and is interpreted to be the result of excessive precipitation, possibly related to the climatic shift towards cooler and wetter conditions referred to as the 2.8 ka event.  相似文献