Ground water potential in fractured aquifers of Ophiolite formations,Port Blair,South Andaman Islands using Electrical Resistivity Tomography (ERT) and Vertical Electrical Sounding (VES)     

Balakrishna  S. Balaji Shrikant Maury  G. Narshimulu 《Journal of the Geological Society of India》2014,83(4):393-402

Ground water occurs in weathered formations of unsaturated zone and fractured rocks of saturated zone. The ground water occurring in the unsaturated zone is not sustainable while the ground water occurring in the fractured rocks are sustainable if properly exploited. But, targeting the productive fractured rocks needs careful evaluation and systematic approach of geophysical survey owing to the heterogeneity, magmatic and metamorphic activities of multiple episodes of rocks. Hence, judicious planning in ground water exploration is warranted because of the huge money involved in drilling, manpower and time factor. In this context, an attempt has been made to locate the fractured rocks of ground water potential in the Ophiolite formations of Port Blair, South Andaman Islands using Electrical Resistivity Tomography (ERT) and Vertical Electrical Soundings (VES) since the ground water database of Andaman and Nicobar islands is poor as not much work has been carried out so far and the ground water is not properly utilised. The ERT have been carried out along different azimuth of fractures to ascertain the resistivities in vertical and horizontal direction and the conductivity and/or the resistivity of the varied fractures was also evaluated by spot VES. The 2-D Electrical Resistivity Images in conjunction with the geoelectrical parameters brought out by VES revealed that E-W fractures are expected to be productive fractures showing more conductivity as it is compared with the NE-SW and NW-SE fractures. The potentiality of the E-W fractures was also validated with the borehole data.  相似文献   

Assessing physical vulnerability in large cities exposed to flash floods and debris flows: the case of Arequipa (Peru)     

Jean-Claude Thouret  Susanne Ettinger  Mathieu Guitton  Olivier Santoni  Christina Magill  Kim Martelli  Giulio Zuccaro  Victor Revilla  Juan Antonio Charca  Anita Arguedas 《Natural Hazards》2014,73(3):1771-1815

Understanding the physical vulnerability of buildings and infrastructure to natural hazards is an essential step in risk assessment for large cities. We have interpreted high spatial resolution images, conducted field surveys, and utilized numerical simulations, in order to assess vulnerability across Arequipa, south Peru, close to the active El Misti volcano. The emphasis of this study was on flash floods and volcanic or non-volcanic hyperconcentrated flows, which recur on average every 3.5 years across the city. We utilized a geographic information system to embed vulnerability and hazard maps as a step to calculate risk for buildings and bridges along the Río Chili valley and two tributaries. A survey of ~1,000 buildings from 46 city blocks, different in age, construction materials, and land usage, provided architectural and structural characteristics. A similar survey of twenty bridges across the three valleys was based on structural, hydraulic, and strategic parameters. Interpretation of high spatial resolution (HSR) satellite images, which allows for quick identification of approximately 69 % of the structural building types, effectively supplemented field data collection. Mapping vulnerability has led us to pinpoint strategic areas in case of future destructive floods or flows. Calculated vulnerability is high if we examine structural criteria alone. We further consider physical setting with the most vulnerable city blocks located on the lowermost terraces, perpendicular or oblique to the flow path. Statistical analysis conducted on 3,015 city blocks, considering nine criteria identified from HSR images, indicated that building-type heterogeneity and the shape of the city blocks, along with building and street network density, are the most discriminant parameters for assessing vulnerability.  相似文献   

Origin of the giant Allard Lake ilmenite ore deposit (Canada) by fractional crystallization,multiple magma pulses and mixing     

Bernard Charlier  Olivier Namur  Simon Malpas  Cédric de Marneffe  Jean-Clair Duchesne  Jacqueline Vander Auwera  Olivier Bolle 《Lithos》2010,117(1-4):119-134

The late-Proterozoic Allard Lake ilmenite deposit is located in the Havre-Saint-Pierre anorthosite complex, part of the allochtonous polycyclic belt of the Grenville Province. Presently the world's largest Fe–Ti oxide deposit, it had a pre-mining amount in excess of 200 Mt at grades over 60 wt.% hemo-ilmenite. The main ore body is a funnel-shaped intrusion, measuring 1.03 × 1.10 km and 100–300 m-thick. Two smaller bodies are separated by faults and anorthosite. The ore is an ilmenite-rich norite (or ilmenitite) made up of hemo-ilmenite (Hem_22.6–29.4, 66.2 wt.% on average), andesine plagioclase (An_45–50), aluminous spinel and locally orthopyroxene. Whole-rock chemical compositions are controlled by the proportions of ilmenite and plagioclase ± orthopyroxene which supports the cumulate origin of the deposit. Ore-forming processes are further constrained by normal and reverse fractionation trends of Cr concentration in cumulus ilmenite that reveal multiple magma emplacements and alternating periods of fractional crystallization and magma mixing. Mixing of magmas produced hybrids located in the stability field of ilmenite resulted in periodic crystallization of ilmenite alone. The unsystematic differentiation trends in the Allard Lake deposit, arising from a succession of magma pulses, hybridisation, and the fractionation of hemo-ilmenite alone or together with plagioclase suggest that the deposit formed within a magma conduit. This dynamic emplacement mechanism associated with continuous gravity driven accumulation of Fe–Ti oxides and possibly plagioclase buoyancy in a fractionating ferrobasalt explains the huge concentration of hemo-ilmenite. The occurrence of sapphirine associated with aluminous spinel and high-alumina orthopyroxene (7.6–9.1 wt.% Al₂O₃) lacking exsolved plagioclase supports the involvement of a metamorphic overprint during the synchronous Ottawan orogeny, which is also responsible for strong textural equilibration and external granule of exsolved aluminous spinel due to slow cooling.  相似文献   

Numerical study of the soil–structure interaction within mining subsidence areas     

Olivier Deck  Harlalka Anirudh 《Computers and Geotechnics》2010

Structures affected by mining subsidence are exposed to heavy damage potential in relation to the induced tensile or compressive horizontal ground strains. This study intends to specify and compare the mining subsidence effect in terms of building transmitted movements or induced stresses, given the soil–structure interaction phenomena produced at the interface between a “stiff” elastic structure and a “flexible” elastoplastic soil.  相似文献   

Dehydration of dioctahedral aluminous phyllosilicates: thermodynamic modelling and implications for thermobarometric estimates   总被引：1，自引：1，他引：0  

Benoît Dubacq  Olivier Vidal  Vincent De Andrade 《Contributions to Mineralogy and Petrology》2010,159(2):159-174

We propose a solid-solution model for dioctahedral aluminous phyllosilicates accounting for the main compositional variations, including hydration, observed in natural smectites, interlayered illite/smectite, illites, and phengites from diagenetic to high-grade metamorphic conditions. The suggested formalism involves dehydrated micas and hydrated pyrophyllite-like thermodynamic end-members. With these end-members, the equilibrium conditions of quartz + water + K-bearing mica-like phyllosilicates of fixed 2:1 composition are represented by a line in P–T space along which the interlayer water content varies. The relevant thermodynamic properties required for the calculation of equilibrium conditions were derived using a set of 250 natural data of known maximal temperature and pressure conditions, which covers a range between 25°C and few MPa to 800°C and 5 GPa. The temperatures calculated at fixed pressure with our model are in fair agreement with those reported in the literature for the 250 natural data. At low temperature and pressure, the amount of interlayer water in K-deficient phengite and illite is predicted to reach 100% of the apparent vacancies, which is consistent with previous values reported in the literature. Although the amount of interlayer water is predicted to decrease with pressure and temperature, it is calculated to be significant in K-deficient phengite from LT–HP pelites metamorphosed at about 350°C, 10 kbar. The presence of molecular water in the interlayer site of such phengites has been confirmed by FTIR mapping. Its implications for P–T estimates are discussed.  相似文献   

Hydraulic conductivity distribution in crystalline rocks, derived from inflows to tunnels and galleries in the Central Alps, Switzerland   总被引：4，自引：3，他引：1  

Olivier Masset  Simon Loew 《Hydrogeology Journal》2010,18(4):863-891

Inflow data from 23 tunnels and galleries, 136 km in length and located in the Aar and Gotthard massifs of the Swiss Alps, have been analyzed with the objective (1) to understand the 3-dimensional spatial distribution of groundwater flow in crystalline basement rocks, (2) to assess the dependency of tunnel inflow rate on depth, tectonic overprint, and lithology, and (3) to derive the distribution of fracture transmissivity and effective hydraulic conductivity at the 100-m scale. Brittle tectonic overprint is shown to be the principal parameter regulating inflow rate and dominates over depth and lithology. The highest early time inflow rate is 1,300 l/s and has been reported from a shallow hydropower gallery intersecting a 200-m wide cataclastic fault zone. The derived lognormal transmissivity distribution is based on 1,361 tunnel intervals with a length of 100 m. Such interval transmissivities range between 10^?9 and 10^?1 m²/s within the first 200–400 m of depth and between 10^?9 and 10^?4 m²/s in the depth interval of 400–1,500 m below ground surface. Outside brittle fault zones, a trend of decreasing transmissivity/hydraulic conductivity with increasing depth is observed for some schistous and gneissic geological units, whereas no trend is identified for the granitic units.  相似文献   

Measuring Hg Isotopes in Bio-Geo-Environmental Reference Materials   总被引：1，自引：0，他引：1  

Nicolas Estrade  Jean Carignan  Jeroen E. Sonke  Olivier F.X. Donard 《Geostandards and Geoanalytical Research》2010,34(1):79-93

With the emergence of new analytical techniques and the expansion of scientific fields explored by using mercury isotopes, the community needs reference materials (RM) to validate and assure the accuracy of the results. The present work investigates (1) the characterisation of secondary RM in order to validate analytical systems, (2) the effects of two complex matrices on isotopic determination using stannous chloride cold vapour generation coupled to MC-ICP-MS (CV-MC-ICP-MS), (3) the effects of multiple digestion techniques for total Hg extraction and (4) the characterisation of nine geo-bio-environmental RM. Two secondary mono-elemental RMs analysed using two different analytical setups yielded isotopic compositions on δ²⁰²Hg of −3.54 ± 0.27‰ (CRPG-F65A, 2SD, n = 38) and +2.59 ± 0.19‰ (CRPG-RL24H, 2SD, n = 30) relative to the CRM NIST SRM 3133. These two RMs cover the whole range of Hg isotopic fractionation in natural samples and are made available to the scientific community. Complex fly ash and hydroxysulfate green rust matrices were synthesised, spiked with NIST SRM 3133, then digested and finally analysed versus the mono-elemental NIST SRM 3133 to show potential effect of these complex matrices during CV-MC-ICP-MS. Three digestions techniques, including traditional acid digestion, microwave digestion and high pressure-high temperature digestion, were applied to the lichen RM BCR-482 in order to compare advantages and drawbacks of these methods. Finally, the isotopic compositions of nine RMs including soils (NIST SRM 2711; GXR-2; GSS-4), sediment (GSD-10), jasperoid (GXR-1), ore deposit (GXR-3), fly ashes (BCR-176; BCR-176R) and lichen (BCR-482) are reported. These selected materials have δ²⁰²Hg values ranging from −1.75‰ to +0.11‰. Some RMs also presented mass-independent fractionation with Δ¹⁹⁹Hg and Δ²⁰¹Hg of up to −0.6‰.  相似文献   

Iron Isotope Variations in Coastal Seawater Determined by Multicollector ICP-MS     

Olivier J. Rouxel  Maureen Auro 《Geostandards and Geoanalytical Research》2010,34(2):135-144

In this paper, we applied a reliable technique for measuring Fe isotope variations in coastal seawater at nanomolar levels. Iron was directly pre-concentrated from acidified seawater samples onto a nitrilotriacetic acid chelating resin and further purified using anion-exchange resin. Sample recovery, determined using a standard addition method, was essentially quantitative. Iron was then determined using a high-resolution multicollector ICP-MS (Neptune) coupled to an ApexQ desolvation introduction system. The external precision for δ⁵⁶Fe values was 0.11‰ (2s) when using total a Fe quantity between 25 and 100 ng. We initially applied this technique to measure the Fe isotope composition of dissolved Fe from several coastal environments in the north-eastern United States and we observed a range of δ⁵⁶Fe values between -0.9‰ and 0.1‰ relative to the IRMM-14 reference material. Iron isotope compositions of several reference water materials for inter-laboratory comparisons were also reported. Our results suggest that iron in coastal seawater, derived from benthic diagenesis and/or groundwater has negative Fe isotopic signatures that are distinct from other iron sources such as atmospheric deposition and rivers.  相似文献   

Zinc in Fish, Crabs, Oysters, and Mangrove Flora and Fauna from Cleveland Bay   总被引：1，自引：0，他引：1  

G.B Jones  P Mercurio  F Olivier 《Marine pollution bulletin》2000,41(7-12):345-352

Zinc in muscle tissue from 28 species of fish, three species of sharks and rays, two species of squid and cuttlefish, and three species of crustacea collected from Cleveland Bay, together with some measurements made on oysters and mangrove flora and fauna are reported. In the fish species the mean Zn concentration in muscle tissue was 4.83 ± 2.82 μg/g wet weight, slightly lower than zinc measurements (7 μg/g wet weight) made in 14 fish species collected from the bay in 1975. Zinc in sharks and rays ranged from 3.5 to 7.2 μg/g wet wt, in squid and cuttlefish 13–16 μg/g wet wt, and in crustacea levels ranged from 14 to 18 μg/g wet wt. Zinc levels in fish varied between species with concentrations well below the ANZECC Maximum Residue Limit of zinc in seafood (150 μg/g wet wt). Although lower zinc concentrations were found in oysters collected from the Townsville Harbour area (2080 μg/g wet wt), compared with previous measurements made 25 years ago at this site, these levels are still above the Maximum Residue Limit for zinc in oysters (1000 μg/g wet wt). Concentrations of zinc in oysters from Orpheus Island (2547 μg/g wet wt), about 74 km away from industrial and urban activity, are also above the safe guideline values. Horseshoe Bay oysters transplanted to Ross Creek accumulated zinc at a rate of about 100 μg/g of oyster tissue per week, suggesting that dissolved zinc levels at this site are elevated, and that oysters rapidly accumulate zinc. Highest concentrations of zinc in mangrove leaves (30–65 μg/g dry wt) occurred in Osbornia octodonta, Exocaria agalocha, and Aegialitus annulata, compared with Ceriops tagal, and Avicennia marina (5–10 μg/g dry wt). No significant difference in zinc concentration occurred between leaves and litter fall for most of these species, with the sole exception of Exocaria, which showed almost a twofold increase in concentration. In seven species of mangrove fauna levels of zinc were very uniform and close to 50 μg/g (dry wt) Telescopium telescopium from the mouth of the Ross Estuary was the exception with levels at 400 μg/g (dry wt).  相似文献   

Magmatic source enrichment by slab-derived melts in a young post-collision setting, central Mindanao (Philippines)   总被引：28，自引：0，他引：28  

Fernando G. Sajona  Ren  C. Maury  Manuel Pubellier  Jacques Leterrier  Herv  Bellon  Joseph Cotten 《Lithos》2000,54(3-4):173-206

Central Mindanao was the locus of a Pliocene (4–5 Ma old) arc–arc collision event followed by basaltic to dacitic magmatism starting at 2.3 Ma, representing the most voluminous volcanic field in the Philippines. Lava compositions range from calc-alkaline to shoshonitic. Adakites and Nb-enriched basalts are among the magmatic products. All the lavas are Na-rich (up to 4.88%), with Na₂O/K₂O ratios from 2.5 to 6.5. Sr, Nd and Pb isotopic compositions are similar to MORB, except for some shoshonitic lavas that have slightly less radiogenic Nd ratios. K-enrichment in basalts can be related to both fractional crystallization (FC) at moderate pressures and to partial melting of an enriched source. Trace element systematics indicate that the sub-central Mindanao mantle is characterized by the presence of garnet, phlogopite, amphibole, and perhaps some titanate phase. The enrichment of this source is attributed to the interaction of slab-derived melts, i.e., adakites, with the arc mantle. This would explain the presence of Nb-enriched basalts, transitional adakites and high-magnesium andesites, as well as the bulk Na-enrichment and relatively unradiogenic character of the central Mindanao lavas. We envision an ion-exchange type of enrichment, in which the HFSE, LILE and LREE, mobilized during slab melting, are preferentially enriched in the metasomatized mantle, resulting in a diversity of post-collision magma compositions. The MORB-like isotopic signatures of the central Mindanao lavas preclude important contributions of slab-derived hydrous fluids, sediments, continental crust or an OIB-type contaminant. Slab melting after cessation of subduction is deemed possible by thermal rebound of previously depressed geotherms. Initial contributions to mantle enrichment in post-collision sites may thus come from slab melts. In most other cases of post-collision magmatism, however, this signature can be easily masked by enrichments coming from other sources, e.g., the continental lithosphere.  相似文献