Melting, carbonic fluids and water recycling in the deep crust: an example from the Limpopo Belt, South Africa

The proposed retrograde orthoamphibole isograd in the Southern Marginal Zone of the Limpopo Belt separates hydrated, amphibolite grade metapelites from their granulite grade precursors and provides an intriguing geological dilemma. Widespread rehydration of metapelitic granulites under conditions of 660–600 °C and ≥0.6 GPa, and CO₂-dominated fluid-inclusion populations appear to suggest thorough flushing of the high-grade crust with an externally derived carbonic fluid. However, past studies of the carbon and oxygen isotope geochemistry of the hydrated rocks have not demonstrated the involvement of any voluminous out of equilibrium’ fluid in the evolution of the rocks. This contribution proposes a model wherein the hydrating fluids are derived from crystallizing anatectic leucosomes, generated by in situ fluid-absent biotite melting along the prograde path. Model equilibrium fluid compositions suggest that reaction between this melt-derived H₂O and biogenic graphite produced CO₂-rich fluid compositions and potentially high fluid:rock ratios at the wet granite solidus. Declining temperature resulted in fluid compositions shifting to higher XH₂O, with the precipitation of graphite essentially at the sites of initial fluid generation, thereby preserving original (pre-metamorphic) isotopic heterogeneities. The hydration pattern of the Southern Marginal Zone appears to be a function of melt migration. In the hydrated zone, leucosomes generally approximate minimum melt compositions and in this zone H₂O was effectively recycled between the prograde and retrograde assemblages. In contrast, leucosomes in the granulite grade portion of the terrane have lost a K₂O- and H₂O-rich melt fraction, and although some hydration has occurred in this zone, orthopyroxene is generally preserved in metapelites. In a general context, in situ crystallization of graphitic partially melted source rocks has the potential to produce high fluid-rock ratios at temperatures close to the wet granite solidus. This single process holds the potential for widespread retrogression of formerly high-grade assemblages, at a variety of aH₂O values, without external fluid input.     

水力坡度在层间氧化带砂岩型铀矿区域预测中的意义

本文根据地下水水动力参数之一──水力坡度所反映出的地下水动力特征和地下水径流强度以及对层间氧化带发育的影响，试图找出适合于层间氧化带发育的水力坡度范围，从而达到利用这一地下水水动力参数指导层间氧化带砂岩型铀矿区域预测工作的目的。     

Analysis of deposition and erosion of Dongting Lake by GIS

The sediments of the Dongting Lake come from four channels (one of them was closed in 1959), connected with the Yangtze River, four tributaries (Lishui, Yuanjiang, Zishui and Xiangjiang) and local area, and some of them are transported into the Yangtze River in Chenglingji, which is located at the exit of the Dongting Lake, some of them deposit into drainage system in the lake region and the rest deposit into the lake. The annual mean sediment is 166,555x104 t, of which 80% come from the four channels, 18% from the four tributaries and 2% from local area, whereas 26% of the total sediments are transported into the Yangtze River and 74% deposited into the lake and the lake drainage system. Based on topographic maps of 1974, 1988 and 1998, and the spatial analysis method with geographic information system (GIS), changes in sediment deposition and erosion are studied in this paper. By overlay analysis of 1974 and 1988, 1988 and 1998, erosion and sediments deposition areas are defined. The main conclusions are: (1) sediment rate in the lake is larger than erosion rate from 1974 to 1998. The mean deposition in the lake is 0.43 m; (2) annual sediment deposition is the same between 1974-1988 and 1988-1998, but the annual volume of deposition and erosion of 1988-1998 is bigger than that in 1974-1988; (3) before the completion of the Three Gorges Reservoir, there will be 7.82x108 m3 of sediments deposited in the lake, which would make the lake silted up by 0.33 m; (4) in the lake, the deposition area is found in the north of the east Dongting Lake, the south-west of the south Dongting Lake, and the east of the west Dongting Lake; while the eroded area is in the south of the east Dongting Lake, the middle of the south Dongting Lake, the west of the west Dongting Lake, as well as Xiangjiang and Lishui river flood channels.     

潮滩盐沼物理过程的研究进展综述

综述了本世纪国外潮滩盐沼堆积、侵蚀机制的研究进展，主要包括潮滩盐沼的粘性泥沙沉积动力机制的分析、对潮滩盐沼的物理过程的详细观测研究、沉积模式研究，以及潮滩盐沼物理过程的知识在海岸防护和其它方面的应用。     

Chemical sensor resolution required for measuring surface fluxes by three common micrometeorological techniques

We define the chemical or compositional resolution required to measure the surface emission/deposition flux of trace constituents under different meteorological conditions by means of the eddy correlation, gradient, and conditional sampling techniques. These chemical resolutions are defined for the full range of different atmospheric conditions and are reported in terms of commonly measured micrometeorological parameters.The National Center for Atmospheric Research is sponsored by the National Science Foundation     

The heterogeneous formation of N2O in air containing NO2, O3 and NH3

In a nighttime system and under relatively dry conditions (about 15 ppm H₂O), the reaction mixture of NO₂, O₃, and NH₃ in purified air turns out to result in the formation of nitrous oxide (N₂O). The experiments were performed in a continuous stirred flow reactor, in the concentration region of 0.02–2 ppm.N₂O is thought to arise through the heterogeneous reaction of gaseous N₂O₅ and absorbed NH₃ at the wall of the reaction vessel % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqaqpepeea0xe9qqVa0l% b9peea0lb9sq-JfrVkFHe9peea0dXdarVe0Fb9pgea0xa9pue9Fve9% Ffc8meGabaqaciGacaGaaeqabaWaaeaaeaaakeaatCvAUfKttLeary% qr1ngBPrgaiuaacqWFOaakcqWFobGtcqWFibasdaWgaaWcbaGae83m% amdabeaakiab-LcaPmaaBaaaleaacqWFHbqyaeqaaOGaey4kaSIaai% ikaiab-5eaonaaBaaaleaacqWFYaGmaeqaaOGae83ta80aaSbaaSqa% aiab-vda1aqabaGccaGGPaWaaSbaaSqaaiaadEgaaeqaaOGaeyOKH4% Qae8Nta40aaSbaaSqaaiab-jdaYaqabaGccqWFpbWtcqGHRaWkcqWF% ibascqWFobGtcqWFpbWtdaWgaaWcbaGae83mamdabeaakiabgUcaRi% ab-HeainaaBaaaleaacqWFYaGmaeqaaOGae83ta8eaaa!59AC!\[(NH_3 )_a + (N_2 O_5 )_g \to N_2 O + HNO_3 + H_2 O\]In principle, there is competition between this reaction and that of adsorbed H₂O with N₂O₅, resulting in the formation of HNO₃. At high water concentrations (RH>75%), no formation of N₂O was found. Although the rate constant of adsorbed NH₃ with gaseous N₂O₅ is much larger than that of the reaction of adsorbed H₂O with gaseous N₂O₅, the significance of the observed N₂O formation for the outside atmosphere is thought to be dependent on the adsorption properties of H₂O and NH₃ on a surface. A number of NH₃ and H₂O adsorption measurements on several materials are discussed.     

震旦纪大塘坡期锰矿的内碎屑结构和重力流沉积

大塘坡组锰矿石由菱锰矿内碎屑和碳泥质基质组成。菱锰矿内碎屑是浅水沉积环境中的锰质沉积物破碎而成。它们沿着盆地斜坡流入深水地区与碳、粘土和粉砂沉积在一起形成内碎屑菱锰矿。一部分矿石有递变层理,具有浊流沉积特征。     

THE ROLE PLAYED BY WASH LOAD DEPOSITION IN THE FORMATION OF DIFFERENT RIVER PATTERNS

ＴＨＥＲＯＬＥＰＬＡＹＥＤＢＹＷＡＳＨＬＯＡＤＤＥＰＯＳＩＴＩＯＮＩＮＴＨＥＦＯＲＭＡＴＩＯＮＯＦＤＩＦＦＥＲＥＮＴＲＩＶＥＲＰＡＴＴＥＲＮＳＴｈｅｌｏｗｅｒｌａｙｅｒｏｆｔｈｅｂｅｄｍａｔｅｒｉａｌｃｏｎｓｉｓｔｓｏｆｔｉｎｅｓａｎｄａｎｄｔｈｅｕｐｐｅｒｌａｙｅｒｃｏｎｓｉｓｔｓｏｆａｍｉｘｔｕｒｅｏｆｃｌａｙ（１０％）ａｎｄｔｉｎｅｓａｎｄ（９０％）．ＮＡＴＵＲＡＬＲＩＶＥＲＳｌ．ＣｈａｎｇｅｏｆｃｈａｎｎｅｌｐａｔｔｅｒｎｓａｌｏｎｇａｒｉｖｅｒｃｏｕｒｓｅＩｔｉｓｃｏｍｍｏｎｔｈａｔｉｎｔｈｅｕｐｐｅｒＰａｒｔｏｆａｎａｌｌｕｖｉａｌｒｉｖｅｒｔｈｅｌｏｎｇｉｔｕｄｉｎａｌｓｌｏｐｅｉｓｓｔｅｅｐａｎｄｔｈｅｒｉｖｅｒｃａｒｒｉｅｓｈｅａｖｙｓｅｄｉｍｅｎｔｌｏａｄ．Ｄｕｅｔｏｔｈｅｓｔｅｅｐｓｌｏｐｅａｎｄａｓｓｏｃｉａｔｅｄｈｉｇｈｖｅｌｏｃｉｔｙｃｌａｙｓｅｔｔｌｅｓｌｉｔｔｌｅｅｖｅｎｏｎｔｌｏｏｄｐｌａｉｎ．Ｆｌｏｏｄｐｌａｉｎｏｒｒｉｖｅｒｈａｎｋｃｏｎｓｉｓｔｓｏｆｓｉｌｔａｎｄｔｉｎｅｓａｎｄ．Ｔｈｅｒｉｖｅｒｂｅｈａｖｅｓａｓａｗａｎｄｅｒｉｎｇｏｎｅ．Ｐａｓｓｉｎｇａｃｅｒｔ     

The Machanism of Bacterial Oxidation of Sulphides

The bacteria used in the experiment are Thiobacillus Ferrooxidans separated from acidic mine water in sulphide deposits. The chemoautotrophic bacteria can act directly on sulphides and accelerate the oxidation of sulphides. The experiment shows that the bacteria, as an important microbial factor of gold's supergenous enrichment within the oxidized zones of sulphide deposits, are helpful to dissolve gold and silver in ferric sulphate. In the bacterial oxidation process, the precipitation of goethite is concerned both with the lower activity of ferric ions and with the existence of carbonates in solution. Meanwhile, the acid-resisting and oxidizing ability of the bacteria will certainly lead up to a microbial way of treating the acidic mine water.