The Hasan Dagi stratovolcano (Central Anatolia, Turkey): evolution from calc-alkaline to alkaline magmatism in a collision zone   总被引：1，自引：0，他引：1  

Catherine Deniel  Erkan Aydar  Alain Gourgaud 《Journal of Volcanology and Geothermal Research》1998,87(1-4)

The Hasan Dagi volcano is one of the two large Plio-Quaternary volcanoes in Cappadocia (Central Anatolia, Turkey). Three stages of edifice construction have been identified for this volcano: Paleovolcano, Mesovolcano and Neovolcano. Most samples from Hasan Dagi volcano are calc-alkaline and define an almost complete trend from basaltic andesite to rhyolite. However, the more recent (Neovolcano) mafic samples are alkaline basalts. The mineralogical and geochemical characteristics of the oldest lavas (Keçikalesi (13 Ma) and Paleo-Hasan Dagi (7 Ma)) are significantly different from those of the younger lavas (Meso- and Neo-Hasan Dagi (<1 Ma)). Calcic plagioclase and pigeonite are typically observed in these older lavas. The Paleovolcano basalts are depleted in alkalis and display a tholeiitic tendency whereas the differentiated lavas are depleted in Na₂O but enriched in K₂O compared to younger lavas. There is an evolution through time towards higher TiO₂, Fe₂O₃^*, MgO, Na₂O and K₂O and lower Al₂O₃ and SiO₂ which is reflected in the basalt compositions. All the basalts display multi-element patterns typical of continental margin magmas with a significant enrichment in LILE (K, Rb, Ba and Th) and LREE and strong (Paleovolcano) to moderate (Meso- and Neovolcano) negative Nb, Zr and Ti anomalies. However, the younger basalts are the most enriched in incompatible elements, in agreement with their alkaline affinities and do not systematically display negative HFSE anomalies. REE data suggest an hydrous amphibole-bearing crystallization history for both Meso- and Neovolcano lavas. The distinction between the older and younger lavas is also apparent in trace element ratios such as Nb/Y, Ti/Y and Th/Y. These ratios indicate the role of a subducted component±crustal contamination in the genesis of the Hasan Dagi lavas, particularly for the oldest lavas (Keçikalesi and Paleo-Hasan Dagi). The decreasing influence of this component through time, over the last 6–7 m.y., has been accompanied by an increasing contribution of melt-enriched lithosphere. Although the range of variation of Sr, Nd and Pb isotopic ratios is small (0.70457–0.70515; 0.51262–0.51273; 18.80–18.94; 15.64–15.69; 38.87–39.10), it also reflects the evolution of the magma sources through time. Indeed, the youngest (Neovolcano) and most primitive basalts display significantly lower ⁸⁷Sr/⁸⁶Sr than the Paleo- and Mesovolcano basalts, whereas the Mesovolcano basalts display more radiogenic Pb than Paleovolcano samples. Magma mixing processes between initially heterogeneous and/or variably contaminated magmas may account for the genesis of the less differentiated and intermediate lavas (48–57% SiO₂). Meso- and Neovolcano differentiated lavas (60–68% SiO₂) are either derived from the analyzed basalts or from more primitive and more depleted magmas by fractional crystallization±some crustal contamination (AFC). Furthermore, the highly differentiated samples (72–75% SiO₂) are not strongly contaminated. The strong calc-alkaline character of Hasan Dagi lavas, in the absence of contemporaneous subduction, must reflect the heritage of the early subduction of the Afro–Arabian plate under the Eurasian plate. The evolution towards alkaline compositions through time is clearly related to the development of extensional tectonics in Central Anatolia in the Late Miocene.  相似文献   

Effect of Complexing Agents (EDTA and ATMP) on the Remobilization of Heavy Metals from a Polluted River Sediment     

François Bordas  Alain C. M. Bourg 《Aquatic Geochemistry》1998,4(2):201-214

EDTA and ATMP are synthetic chelatingagents used in many industrial applications. Becauseof their low biodegradability, they are present inmany aquatic systems where their strong complexingcapacities can modify the transfer of toxic heavymetals between solid and liquid phases.The remobilization of Cu, Pb and Cd from pollutedsuperficial river sediments in the presence of twosynthetic organic ligands (a polycarboxylate, EDTA,and a phosphonate, ATMP) is investigated as a functionof reaction time to determine the time necessary toreach dissolutive equilibrium, and as a fonction ofthe complexing agent concentration.The dissolutive equilibrium times are similar (10 to20 hours) and the solubilizing power of ATMP isslightly lower than that of EDTA. The curves ofsolubilization of metals in the presence of thecomplexing agents present a shape of a chelateconcentration desorption edge, for a chelate rangebetween 10^-5 to 10^-3 mol L^-1, thesolubilised metals increasing dramatically. Thisremobilization is the result of a competition betweenassociation with the solid phase and dissolvedcomplexation. With EDTA, the desorption order ofmetals seems to be imposed by association with thesolid. For ATMP is it the chelate complexing strengthwhich determines this order.  相似文献   

Geochemical and isotopic evidence for seawater contamination of the hydrothermal system of Taal Volcano, Luzon, the Philippines     

Pierre Delmelle  Minoru Kusakabe  Alain Bernard  Tobias Fischer  Simon de Brouwer  Esfeca del Mundo 《Bulletin of Volcanology》1998,59(8):562-576

 The hydrologic structure of Taal Volcano has favored development of an extensive hydrothermal system whose prominent feature is the acidic Main Crater Lake (pH<3) lying in the center of an active vent complex, which is surrounded by a slightly alkaline caldera lake (Lake Taal). This peculiar situation makes Taal prone to frequent, and sometimes catastrophic, hydrovolcanic eruptions. Fumaroles, hot springs, and lake waters were sampled in 1991, 1992, and 1995 in order to develop a geochemical model for the hydrothermal system. The low-temperature fumarole compositions indicate strong interaction of magmatic vapors with the hydrothermal system under relatively oxidizing conditions. The thermal waters consist of highly, moderately, and weakly mineralized solutions, but none of them corresponds to either water–rock equilibrium or rock dissolution. The concentrated discharges have high Na contents (>3500 mg/kg) and low SO₄/Cl ratios (<0.3). The Br/Cl ratio of most samples suggests incorporation of seawater into the hydrothermal system. Water and dissolved sulfate isotopic compositions reveal that the Main Crater Lake and spring discharges are derived from a deep parent fluid (T≈300  °C), which is a mixture of seawater, volcanic water, and Lake Taal water. The volcanic end member is probably produced in the magmatic-hydrothermal environment during absorption of high-temperature gases into groundwater. Boiling and mixing of the parent water give rise to the range of chemical and isotopic characteristics observed in the thermal discharges. Incursion of seawater from the coastal region to the central part of the volcano is supported by the low water levels of the lakes and by the fact that Lake Taal was directly connected to the China sea until the sixteenth century. The depth to the seawater-meteoric water interface is calculated to be 80 and 160 m for the Main Crater Lake and Lake Taal, respectively. Additional data are required to infer the hydrologic structure of Taal. Geochemical surveillance of the Main Crater Lake using the SO₄/Cl, Na/K, or Mg/Cl ratio cannot be applied straightforwardly due to the presence of seawater in the hydrothermal system. Received: 12 February 1997 / Accepted: 26 January 1998  相似文献   

Detrital transport of metals by glaciers, an example from the Pinchi Mine, central British Columbia     

Alain Plouffe 《Environmental Geology》1998,33(2-3):183-196

 Abundant cinnabar (HgS) mineralization is associated with the Pinchi Fault in central British Columbia. Two formerly producing mercury mines have been developed on this fault: Pinchi and Bralorne Takla. The mercury content of till (a sediment type directly deposited by glaciers) in the area of this fault is primarily controlled by the occurrence of cinnabar mineralization in bedrock and the direction of ice flow. Cinnabar-bearing bedrock was eroded by glaciers, transported in the direction of ice flow, and deposited "down-ice" from its source. An example of such a dispersal train is documented for the Pinchi Mine area where mercury ore was transported over a distance of 12 km, as measured in the clay-sized fraction (< 0.002 mm) of till, and could have been transported over 24 km according to heavy mineral concentrates (specific gravity >3.3) of this same sediment. Antimony, chromium, and nickel dispersal trains were also detected in the region. These data indicate that natural glacial processes can result in the "mobilization" of metals in the surficial environment, a factor which has to be considered at mine sites in glaciated terrain, where mine reclamation and remediation measures are now required. Received: 31 October 1996 · Accepted: 27 May 1997  相似文献   

Premiers résultats d'une étude géophysique sur le flanc nord des glissements de Storegga (Norvège)     

Hervé Nouzé  Isabelle Contrucci  Jean-Paul Foucher  Bruno Marsset  Yannick Thomas  Estelle Thereau  Alain Normand  Éliane Le Drezen  Stéphane Didailler  Jean-Pierre Regnault  Sandie Le Conte  Stéphanie Guidart  Wim Lekens  Simon Dean  Alexandre Throo 《Comptes Rendus Geoscience》2004,336(13):1181-1189

The Storegga slides, off Norway, are among the largest submarine slides ever known on a continental slope. The HYDRATECH cruise on N/O Le Suroît aimed at a high-resolution survey of an area at the northern boundary of the slides. This survey images in great detail the bottom simulating reflector (BSR) extent and properties, the various fluid escape structures and the sediment deformations. The combination and the quality of the data help to understand the still poorly constrained relationships between fluid escapes, gas hydrates and slope stability in the survey area. To cite this article: H. Nouzé et al., C. R. Geoscience 336 (2004).  相似文献   

Trace element and isotope (Sr, Nd) geochemistry of porphyry- and skarn-mineralising Late Cretaceous intrusions from Banat, western South Carpathians, Romania   总被引：2，自引：0，他引：2  

Alain Dupont  Jacqueline Vander Auwera  Christian Pin  Ştefan Marincea  Tudor Berza 《Mineralium Deposita》2002,37(6-7):568-586

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The growth of point source plumes at Rayleigh numbers up to 10⁸ and Prandtl numbers up to 1000     

Catherine Hier Majumder  Alain P. Vincent  David A. Yuen 《Visual Geosciences》2002,7(1):1-9

Two-dimensional numerical simulations were conducted of the growth of thermal plumes from a point heat source at Rayleigh numbers up to 108 and Prandtl numbers up to 1000. Scaling the convection equations by the free fall velocity rather than the thermal diffusivity, increased the Prandtl number range available to numerical simulation by one order of magnitude from Prandtl number 100 to 1000. We present animations showing how the plumes grow with time for different Prandtl numbers. Plumes with Prandtl numbers around 7 (water) were found to be unstable to sinuous instabilities; whereas those at Prandtl numbers of 1000 had straight stems and fewer sinuous instabilities. Wavelet analysis was used to analyze the scales at which plumes initiated, and the scales at which sinuous instabilities occurred. The scale of both the plume structures and instabilities was found to decrease with Prandtl number.  相似文献   

Geostatistics of near-surface moisture in bare cultivated organic soils   总被引：4，自引：0，他引：4  

Franois Anctil  Renaud Mathieu  Lon-tienne Parent  Alain A. Viau  Mathali Sbih  Masoud Hessami 《Journal of Hydrology》2002,260(1-4):30-37

The aim of this study was to characterise fine scale patterns of organic soil moisture content in the top 5 cm by means of semi-variogram modelling. Soil moisture content was observed along a transect on 2 occasions, early in the 1999 growing season to avoid any influences originating from vegetation and cultural practices. Soil moisture values were found to be normally distributed and were not significantly correlated with the soil organic matter content. Many similarities were depicted between the exponential semi-variograms characteristics of this study and another one in mineral soils, reported in the literature, except for the much higher sills associated with organic soils. Of particular interest were similar correlation lengths, indicating that a correlation range of the order of 100 m should be expected for mineral soils and for the level of moisture and organic matter contents found in this study.  相似文献   

Reservoir lifetime and heat recovery factor in geothermal aquifers used for urban heating   总被引：1，自引：0，他引：1  

Alain C. Gringarten 《Pure and Applied Geophysics》1978,117(1-2):297-308

Simple models are discussed to evaluate reservoir lifetime and heat recovery factor in geothermal aquifers used for urban heating. By comparing various single well and doublet production schemes, it is shown that reinjection of heat depleted water greatly enhances heat recovery and reservoir lifetime, and can be optimized for maximum heat production. It is concluded that geothermal aquifer production should be unitized, as is already done in oil and gas reservoirs.Nomenclature a distance between doublets in multi-doublet patterns, meters - A area of aquifer at base temperature, m² drainage area of individual doublets in multidoublet patterns, m² - D distance between doublet wells, meters - h aquifer thickness, meters - H water head, meters - Q production rate, m³/sec. - r _e aquifer radius, meters - r _w well radius, meters - R _g heat recovery factor, fraction - S water level drawdown, meters - t producing time, sec. - T aquifer transmissivity, m²/sec. - v stream-channel water velocity, m/sec. - actual temperature change, °C - theoretical temperature change, °C - water temperature, °C - heat conductivity, W/m/°C - _r rock heat conductivity, W/m/°C - _aC_a aquifer heat capacity, J/m³/°C - _aC_r rock heat capacity, J/m³/°C - _WC_W water heat capacity, J/m³/°C - aquifer porosity, fraction  相似文献   

Anabaena bergii var.limnetica,nov. var., Cyanophyceae,Nostocaceae     

Alain Couté  Hans Rudolf Preisig 《Aquatic Sciences - Research Across Boundaries》1978,40(2):374-383

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