Argiles et zéolites dans l'altération d'un volcan bouclier en milieu tropical (Le Piton des Neiges,La Réunion)     

Laurent Bret  Jean-Lambert Join  Xavier Legal  Jean Coudray  Bertrand Fritz 《Comptes Rendus Geoscience》2003,335(14):1031-1038

The drilling of a gallery through the Roche-Écrite massif (Reunion Island) allowed to sample the old formations of the ‘Piton des Neiges’ volcano. The mineralogical study of the alteration products of the formations showed significant variations of the zeolites/clay minerals ratio depending on the location of the rocks in the volcano. The abundance of zeolites in the formation near the surface hydrographic network or the underground water drainage system seems to be due to the physicochemical processes favouring zeolites in more open systems in their competition with secondary clays. To cite this article: L. Bret et al., C. R. Geoscience 335 (2003).  相似文献   

The Influence of the El Niño Southern Oscillation on Suspended Sediment Load Variability in a Seasonally Humid Tropical Setting: Panuco Basin, Mexico     

Paul F. Hudson 《Geografiska Annaler: Series A, Physical Geography》2003,85(3-4):263-275

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The landslide hazard and human vulnerability in La Paz City, Bolivia   总被引：4，自引：0，他引：4  

GREG O'HARE  SARA RIVAS† 《The Geographical journal》2005,171(3):239-258

Landslides in the city of La Paz, Bolivia are complex in space and time. Their distribution within the city is differentiated by geographical variations in slope gradient, the nature of overlying surface deposits, and drainage density patterns. When mapped, the distribution of the most landslide-prone locations in the city coincides with the most mobile surface deposits on the higher and steeper slopes of the city. The timing of landslides is triggered when slope materials become saturated with moisture by rainfall, stream water, water seepage from high surrounding water tables, and from domestic sources. Landslide frequencies over the last 40 years show the role of inter-annual variations in summer rainfalls, especially the late summer period (Jan–Mar), and rising water tables connected to Lake Titicaca. Associations with ENSO events, both warm (El Nino) and cold (La Nina), prove negative, pointing to the importance of moisture sources from the north, south and east (Amazon) but not from the west (Pacific). The most vulnerable group exposed to the landslide hazard comprise the inhabitants of the self-built informal housing areas who occupy the more elevated steeper slopes of the northern part of the city. But societal vulnerability to earth movement in the city is widespread and interconnected. Higher income groups in the southern part of the city are affected by slower, if less dramatic, forms of land failure, and rich housing in downstream areas of the city are impacted by flash flooding encouraged by deforestation on the northern hill slopes where the poor live. Two case studies highlight the vulnerability and plight of the inhabitants of the self-built settlements in the aftermath of a major landslide, and a brief discussion of hazard mitigation and the importance of building hazard resilient communities concludes the paper.  相似文献   

Remote and in situ plume measurements of acid gas release from La Soufrière volcano, Guadeloupe     

Marie-Lise Bernard  Jack Molini  Rose-Helen Petit  Franois Beauducel  Gilbert Hammouya  Guy Marion 《Journal of Volcanology and Geothermal Research》2006,150(4):395-409

This paper presents the first remote measurements of La Soufrière gas emissions since the fumarolic and seismic reactivation in 1992. The chemical composition of the plumes has been measured from May 2003 to September 2004 using an Open Path Fourier Transform InfraRed (OP-FTIR) spectrometer, up to 15 m downwind the South Crater. HCl is clearly detected (concentration between 2.4 and 12 ppmv) whereas SO₂ and H₂S generally remain below the detection limit of the OP-FTIR. Direct measurements of SO₂ and H₂S near the South Crater with a Lancom III analyzer show a fast decrease of their concentrations with the distance. Calculated Cl / S mass ratios are high: from 9.4 ± 1.7 at 15 m from the vent to 2.8 ± 0.6 at 140 m. The enrichment in HCl of the gas emitted at La Soufrière, observed since 1998, corresponds to the degassing of a magma enriched in Cl and depleted in S. This result agrees with isotopic measurements which suggest a magmatic origin of the gases. Readjustments inside the volcanic system may have taken place during the seismic activity beginning in 1992 and enhance the transfer of magmatic gases to the summit.  相似文献   

Sources of very high heavy metal content in soils of volcanic island (La Réunion)     

Emmanuel D&#x;lsch  Herv Saint Macary  Virginie Van de Kerchove 《Journal of Geochemical Exploration》2006,88(1-3):194

The objective of this study was to conduct an inventory of heavy metal concentrations (Cd, Cr, Cu, Hg, Ni, Pb and Zn) in the soils of La Réunion. 39 sampling sites were selected to cover the distribution of soils of the island. The results show that soils of La Réunion are rich in heavy metals: most of them exceed the French standard values beyond which sewage sludge spreading is not authorized. To identify the sources of heavy metals, we used: (i) the relationship between the heavy metal content in soils and the origin of the volcanic parent material; (ii) the comparison of heavy metal content between cultivated and uncultivated soils; and (iii) the heavy metal distribution in soil profiles. Cd and Pb evolution in soil profiles indicate an impact of human activities. High Hg concentrations in soils can be explained by the volcanic activity of the island. For Cr, Cu, Ni and Zn, we demonstrate that high concentrations in soils are mainly determined by the natural pedo-geochemical background.  相似文献   

Role of the shale tectonics on the evolution of the Eastern Venezuelan Cenozoic thrust and fold belt     

Leo Duerto  Ken McClay 《Marine and Petroleum Geology》2011,28(1):81-108

This paper presents a structural and stratigraphic analysis of the foreland-fold-belt of the Eastern Venezuelan Basin and the main conclusions about shale tectonic mechanisms in the area. The deformation of the foreland-fold-belt has been investigated analyzing the growth strata architecture preserved on the structure fold limbs. Three contractional episodes are proposed for the Eastern Venezuelan Basin: 1) Oligocene to middle Miocene, 2) late Miocene to Pliocene and 3) Pleistocene. The first episode produced contractional listric faults inside the shale and long displacement blind thrusts in the underlying Cretaceous units. The second episode produced the deformation of the Cenozoic strata into overlapping east-west-trending, convex northward anticlines that covers more than 200 kilometers in length and 40 kilometers wide, break-through normal faults product of a high sedimentary load that overcomes contraction and the formation of short-displacement blind thrusts in the underlying Cretaceous units. The last episode is related to an oblique compression and the formation of high angle extensional faults with dextral movement and NW-SE strike. The role of the shale tectonics in the evolution implies that shale deforms in two stages: 1) folding and 2) normal faulting of the crest of the anticline (Break through normal faulting). Folding controlled the sediment distribution during most of the Neogene strata, while the normal faulting of the anticlines represent basin potential for hydrocarbon. The best potential hydrocarbon plays in the basin are related to oblique-collision restricted basins and controlled by break-through normal faults and the presence of NW-SE strike faults that connect the HC source with the reservoirs. Results from this research imply that the role of sedimentation is fundamental for the overburden sand distribution and tectonic constrain of the folds.  相似文献   

大气环流模式对ENSO时间尺度风应力距平的模拟     

吴秋霞  倪允琪 《热带气象学报》1997,13(3):227-236

通过与观测作比较。评估低分辨率的大气环流模式模拟的风场，模式风场是使用观测海温场外强迫，从１９７９年到１９８８年共积分十年得到的，模式输出为月平均值。结果表明，模式能够相当真实地模拟出风距平场的演变，用风应力距平强迫简单模式，积分十年（１９７９－１９８８），得到的海温距平场（月平均值）和观测海温距平场作比较，模式结果较真实地模拟了１９８２－１９８３年及１９８６／１９８７年暖事件的赤道地区海温距平场  相似文献   

矾山磷铁矿床稀土元素地球化学特征   总被引：3，自引：0，他引：3  

程春 《化工矿产地质》2001,23(2):104-108

矾山磷铁矿床赋存于矾山杂岩体内 ,呈层状产出 ,是由深源富钾铁镁质岩浆演化而形成的晚期矿床。矾山杂岩体由三期侵入岩和脉岩组成 ,矿床产于第一期侵入岩中。第一期侵入岩较其它期次侵入岩REE含量高 ,按辉石岩—黑云母辉石岩—磷灰石岩的顺序增加。矿床稀土元素地球化学特征及主要元素含量表明 :在岩桨演化晚期 ,在贫硅和缺少足够“Ca2 +”的条件下 ,稀土元素极易代替“Ca2 +”而进入磷灰石晶格形成补尝类质同象。这对于研究矿床形成的物理化学环境和岩桨的演化具有重要意义。  相似文献   

热带太平洋表面水中CO₂对El Niño事件响应的数值模拟   总被引：3，自引：0，他引：3  

邢如楠  王彰贵 《气象学报》2001,59(3):308-317

文中用一个带生物泵的三维全球海洋碳循环模式模拟了热带太平洋表面水中CO2总量(TCO2)在ElNi  相似文献   

近百年ElNino/LaNina事件与北京气候相关性分析   总被引：8，自引：0，他引：8       下载免费PDF全文

刘桂莲  张明庆 《气象》2001,27(2):3-6

通过对近百年El Nino/La Nina事件与北京气候相关性研究发现，El Nino/La Nina事件与北京夏季（6－8月）降水、平均最高气温（7月）和冬季（1月）平均最低气温之间相互关系显著。El Nino事件与夏季降水、冬季平均最低气温呈负相关，与夏季平均最高气温呈正相关，造成降水减少，气温年较差较大，大陆性增强的气候特点。La Nina事件与夏季降水、冬季平均最低气温呈正相关，与夏季平均最高气温呈负关，使降水增加，气温年较差减小，大陆性减弱的气候特点。  相似文献