A petrologic, geochemical and Sr–Nd isotopic study on contact metamorphism and degassing of Devonian evaporites in the Norilsk aureoles, Siberia     

Kwan-Nang Pang  Nicholas Arndt  Henrik Svensen  Sverre Planke  Alexander Polozov  Stephane Polteau  Yoshiyuki Iizuka  Sun-Lin Chung 《Contributions to Mineralogy and Petrology》2013,165(4):683-704

Devonian evaporites and associated sedimentary rocks in the Norilsk region were contact metamorphosed during emplacement of mafic sills that form part of the end-Permian (~252 Ma) Siberian Traps. We present mineralogical, geochemical and Sr–Nd isotopic data on sedimentary rocks unaffected by metamorphism, and meta-sedimentary rocks from selected contact aureoles at Norilsk, to examine the mechanisms responsible for magma-evaporite interaction and its relation to the end-Permian environmental crisis. The sedimentary rocks include massive anhydrite, rock salt, dolostone, calcareous siltstones and shale, and the meta-sedimentary rocks comprise calcareous hornfels, siliceous hornfels and minor meta-anhydrite and meta-sandstone. Contact metamorphism took place at low pressure and at maximum temperatures corresponding to the phlogopite-diopside stability field. Calcareous hornfels have high CaO, MgO, CΟ₂, SΟ₃, low SiO₂ and initial Sr isotopic ratios of 0.7079–0.7092, features indicative of calcareous siltstone protoliths. Siliceous hornfels, in contrast, have high SiO₂, Al₂O₃, Na₂O, low in other major element oxides and initial Sr isotopic ratios of 0.7083–0.7152, consistent with pelitic or shaley protoliths. Loss of CO₂ in a subset of calcareous hornfels can be explained by decarbonation reactions during metamorphism, but release of SO₂ from evaporites cannot be accounted for by a similar mechanism. Occurrences of wollastonite and a variety of hydrous minerals in the calcareous hornfels are consistent with equilibration with hydrous fluid, which was capable of leaching large quantities of anhydrite in the presence of dissolved NaCl. In this way, substantial sediment-derived sulfur could have been mobilized, incorporated into the magmatic system and released to the atmosphere. The release of CO₂ and SO₂ from Siberian evaporites added to the variety of toxic gases generated during metamorphism of organic matter, coal and rock salt, contributing to the end-Permian environmental crisis.  相似文献   

极端干旱条件下策勒绿洲引种植物水分生理特征研究          下载免费PDF全文

彭守兰  曾凡江  刘波  张利刚  罗维成  宋聪  Stefan K.Arndt  彭慧清 《干旱区地理》2013,36(3):457-466

在塔克拉玛干沙漠南缘的中国科学院策勒沙漠研究站植物引种筛选实验区内,以3 a生文冠果、花棒和紫叶小檗为实验材料,研究三种植物经历持续干旱到短期复水过程中的生理生态响应。结果表明：（1）干旱复水后花棒和紫叶小檗的chla、chlb、叶绿素总量以及chla/b值均随土壤含水量的增加而显著增加,文冠果的叶绿素及其组分含量减少。水分变化对chla含量影响较大。（2）三种植物的MDA含量、SS含量在复水后并没有减少,而是显著的增加,文冠果的增加量最大;各物种的脯氨酸的含量降低,紫叶小糪减少的最多。（3）三种植物的清晨水势和正午水势随土壤水分含量的增加而降低,花棒和紫叶小檗的水势变化较小,水分亏缺迹象不显著。文冠果和花棒的抗逆性较强,而紫叶小檗对水分变化比较敏感。本研究结果可为研究区引种植物的适应性及防护林建设中的植物种选择提供理论参考。  相似文献   

Changes in optical properties, chemistry, and micropore and mesopore characteristics of bituminous coal at the contact with dikes in the Illinois Basin   总被引：2，自引：0，他引：2  

M. Mastalerz  A. Drobniak  A. Schimmelmann 《International Journal of Coal Geology》2009,77(3-4):310-319

Changes in high-volatile bituminous coal (Pennsylvanian) near contacts with two volcanic intrusions in Illinois were investigated with respect to optical properties, coal chemistry, and coal pore structure. Vitrinite reflectance (R_o) increases from 0.62% to 5.03% within a distance of 5.5 m from the larger dike, and from 0.63% to 3.71% within 3.3 m from the small dike. Elemental chemistry of the coal shows distinct reductions in hydrogen and nitrogen content close to the intrusions. No trend was observed for total sulfur content, but decreases in sulfate content towards the dikes indicate thermochemical sulfate reduction (TSR). Contact-metamorphism has a dramatic effect on coal porosity, and microporosity in particular. Around the large dike, the micropore volume, after a slight initial increase, progressively decreases from 0.0417 cm³/g in coal situated 4.7 m from the intrusive contact to 0.0126 cm³/g at the contact. Strongly decreasing mesopore and micropore volumes in the altered zone, together with frequent cleat and fracture filling by calcite, indicate deteriorating conditions for both coalbed gas sorption and gas transmissibility.  相似文献   

The discrete and localized nature of the variable emission from active regions     

Martina Belz Arndt  Shadia Rifai Habbal  Margarita Karovska 《Solar physics》1994,150(1-2):165-178

Using data from the Extreme Ultraviolet (EUV) Spectroheliometer onSkylab, we study the empirical characteristics of the variable emission in active regions. These simultaneous multi-wavelength observations clearly confirm that active regions consist of a complex of loops at different temperatures. The variable emission from this complex has very well-defined properties that can be quantitatively summarized as follows: (1) It is localized predominantly around the footpoints where it occurs at discrete locations. (2) The strongest variability does not necessarily coincide with the most intense emission. (3) The fraction of the area of the footpoints,δn/N, that exhibits variable emission, varies by ±15% as a function of time, at any of the wavelengths measured. It also varies very little from footpoint to footpoint. (4) This fractional variation is temperature dependent with a maximum around 10⁵ K. (5) The ratio of the intensity of the variable to the average background emission, δI/Ī, also changes with temperature. In addition, we find that these distinctive characteristics persist even when flares occur within the active region.  相似文献   

Suevite breccia from the Ries crater,Germany: Origin,cooling history and devitrification of impact glasses     

W. V. Engelhardt  J. Arndt  B. Fecker  H. G. Pankau 《Meteoritics & planetary science》1995,30(3):279-293

Abstract— The distribution and petrography of surficial suevite breccias of the Ries impact crater in Southern Germany are reviewed, and the morphology, petrography and chemical composition of impact glasses in suevite breccias and their postdepositional devitrification is synthesized. Origin and thermal history of suevite breccia and suevite glasses are inferred from these data and from recent results of cooling and crystallization experiments with suevite glass melts under controlled conditions. In a montmorillonitic groundmass, the suevite breccia contains pieces of glass, up to some decimeters in size, and crystalline rock clasts of all stages of shock metamorphism. The glass particles originated in impact melt of basement gneisses and cooled by adiabatic pressure release from ～80 GPa to atmospheric pressure during ejection from the crater. They were deposited on the ground together with the other suevite components at a temperature of ～750 °C. Fractured glass pieces in the breccia show that during deposition of the suevite the temperature was below the temperature at which undercooled melt transforms to rigid glass. The suevite cooled after deposition mainly by convection of heat by emanating gases and vapors. In chilled layers at the base and at the top of suevite deposits, the glasses are preserved in vitreous state. Between these zones, the glasses were devitrified, yet crystallization of pyroxene, plagioclase and magnetite took place below the glass-transformation temperature. Annealing experiments show that this unusual devitrification below the transformation temperature can be explained by the impact origin of suevite glasses. Due to rapid adiabatic cooling on decompression, the glasses were oversaturated with water and internally strained. Under these conditions, devitrification, especially the formation of plagioclase, was possible at temperatures below the transformation range. The origin from adiabatically cooled impact melt of deep-seated rocks distinguishes water-bearing suevite glasses from the Ries-derived, water-free moldavite tektites, which are interpreted as condensates of vaporized, surficial sediments (Engelhardt et al., 1987).  相似文献   

Rivers of North-Rhine Westphalia revisited: Tracing changes in river chemistry   总被引：1，自引：0，他引：1  

Andrea Stgbauer  Harald Strauss  Julia Arndt  Victoria Marek  Florian Einsiedl  Robert van Geldern 《Applied Geochemistry》2008,23(12):3290-3304

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Geochronology and geochemistry of the Late Triassic Longtan pluton in South China: termination of the crustal melting and Indosinian orogenesis   总被引：5，自引：0，他引：5  

Liang Qiu  Dan-Ping Yan  Mei-Fu Zhou  Nicholas T. Arndt  Shuang-Li Tang  Liang Qi 《International Journal of Earth Sciences》2014,103(3):649-666

The Indosinian orogeny is recorded by Triassic angular unconformities in Vietnam and South China and by widely occurring granitoids in the Yunkai-Nanling and the Xuefengshan belts of South China. The Longtan pluton in the northwestern part of the Xuefengshan belt is a typical high-K, calc-alkaline, I-type granitoid, which can shed light on the relationship between the Indosinian tectonic and magmatic activity in the region. Three precise zircon U–Pb ages yielded a mean of 218 ± 0.8 Ma, which is taken as the age of crystallization. The pluton consists of both granodiorite (64.59–68.01 % SiO₂ and 3.25–4.22 % K₂O) and granite (70.49–71.80 % SiO₂ and 4.07–4.70 % K₂O). The granodiorites are characterized by relatively high Mg# (54–57), low contents of Na₂O (3.2–4.3 wt%), low abundances of incompatible elements (LILE, Nb and P), high initial ⁸⁷Sr/⁸⁶Sr (0.7175–0.7184) and negative ε_Nd(t) (?9.98 to ?9.72). REE patterns show moderate fractionation ((La/Yb)_cn = 8.07–18.80) with negative Eu anomalies (Eu/Eu* = 0.62–0.86). Compared with the granodiorite, the granite has a wider range of Mg# (49–59), lower contents of Na₂O (2.8–4.2 wt%), higher initial ⁸⁷Sr/⁸⁶Sr (0.7232–0.7243) and more negative ε_Nd(t) (?12.07 to ?11.24) values. REE patterns are relatively flat ((La/Yb)_cn = 14.73–29.37) with smaller negative Eu anomalies (Eu/Eu* = 0.48–0.63). The granodiorite has lower K₂O/Na₂O and Al₂O₃/(MgO + FeO_Tot) values than the granite. Based on major and trace element geochemistry and Sr–Nd isotopes, we interpret the Longtan granodioritic magma to have been derived by partial melting of interlayered Proterozoic metabasaltic to metatonalitic source rocks, whereas the granite was probably derived from a mixture of Proterozoic metagraywackes and metaigneous rocks. Field, petrographic and geochemical evidence indicate that partial melting and fractional crystallization were the dominant mechanism in the evolution of the pluton. The Longtan granodiorites and granites are petrologically and geochemically similar to typical Indosinian varieties and are considered to have been produced in a similar manner. The Indosinian granitoids in the region show a magmatic peak age of ~238 Ma from the Yunkai-Nanling belt in the southeast and a magmatic peak age of ~218 Ma of the Xuefengshan belt to the northwest. These early and late magmatic episodes of the Indosinian granitoids also display slight variations of regular compositions, ε_Nd(t) values and T _DM ages. Thus, we propose a syncollisional extension model that Indosinian granitoids were generated by decompressional partial melting of crustal materials triggered by two extensions during collision of the Indochina and South China blocks. The Longtan pluton in the northwesternmost part of the orogenic belt marks the termination of the Indosinian magmatism and orogenesis.  相似文献   

Modelling Estuarine Biogeochemical Dynamics: From the Local to the Global Scale     

Pierre Regnier  Sandra Arndt  Nicolas Goossens  Chiara Volta  Goulven G. Laruelle  Ronny Lauerwald  Jens Hartmann 《Aquatic Geochemistry》2013,19(5-6):591-626

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http://www.sciencedirect.com/science/article/pii/S1674987113000327   总被引：1，自引：0，他引：1  

Arnaud Pecher  Nicholas Arndt  Alexander Jean  Arthur Bauville  Clement Ganino  Charlotte Athurion 《地学前缘(英文版)》2013,4(5):571-581

The Panzhihua intrusion in southwest China is part of the Emeishan large igneous province and host of a large Fe-Ti-V ore deposit.In previous interpretations it was considered to be a layered,differentiated sill with the ore deposits at its base.New structural and petrological data suggest instead that the intrusion has an open S-shape,with two near-concordant segments joined by a discordant dyke-like segment. During emplacement of the main intrusion,multiple generations of mafic dykes invaded carbonate wall rocks,producing a large contact aureole.In the central segment,magmatic layering is oriented oblique to the walls of the intrusion.This layering cannot have formed by crystal settling or in-situ growth on the floor of the intrusion;instead we propose that it resulted from inward solidification of multiple,individually operating,convection cells.Ore formation was triggered by interaction of magma with carbonate wall rocks.  相似文献   

Modeling and Simulation of Supercavity with Inertial Force in the Horizontal Curvilinear Motion     

邹望  于开平  R. E. A. Arndt  张广 《海洋工程》2014,28(1):31-42

To make a curvilinear motion in the horizontal plane is one of the most contents for realizing the maneuverability of the supercavitating vehicle. It is significant to achieve the controllability and maneuverability of the vehicle in three dimensions both theoretically and practically on research. Models of angle of attack, gravity and inertial force effects on the supercavity in the horizontal curvilinear motion are established, respectively. The supercavity is simulated based on these models in combination with Logvinovich model and the unsteady gas-leakage rate model at the given ventilation rate, and the effect of the inertial force on it is analyzed numerically. Results show that the maximum deviation of the center line of the cross section of supercavity towards the outward normal direction of its trajectory increases as the cavitation number or curvature radius decrease and always occur in the tail because of the increase of inertial effects along the axis of supercavity from the cavitator when other models and flow parameters are constant for the given trajectory curvature. For the variable curvature, the supercavity sheds due to its instability caused by the time-varying angle of attack. The deviation increases along the length of supercavity if the curvature remains the same sign.  相似文献