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961.
Martin Reich Carlos Palacios Miguel A. Parada Udo Fehn Eion M. Cameron Matthew I. Leybourne Alejandro Zúñiga 《Mineralium Deposita》2008,43(6):663-675
The presence of large amounts of atacamite in oxide zones from ore deposits in the Atacama Desert of northern Chile requires
saline solutions for its formation and hyperarid climate conditions for its preservation. We investigated the nature and origin
of atacamite-forming solutions by means of coupling groundwater geochemical analyses with fluid inclusion data, high-resolution
mineralogical observations, and chlorine-36 (36Cl) data in atacamite from the Mantos Blancos and Spence Cu deposits. In both deposits, the salinities of fluid inclusions
in atacamite are comparable to those measured in saline groundwaters sampled from drill holes. The average salinity of fluid
inclusions in atacamite for the Mantos Blancos and Spence deposits (~7–9 and 2–3 wt.% NaCleq, respectively) are strongly correlated to the salinities at which gypsum supersaturates from groundwaters in both deposits
(total dissolved solids ~5–9 and 1–3 wt.% NaCleq, respectively). This correlation is confirmed by transmission electron microscopy observations of atacamite-bearing samples,
revealing an intimate association between atacamite and gypsum that can be traced down to the nanometer scale. 36Cl data in atacamite provide new lines of evidence concerning the origin and age of the saline waters that formed atacamite
in various stratabound and porphyry Cu deposits from the Atacama Desert. All atacamite samples show very low 36Cl-to-Cl ratios (11 × 10−15 to 28 × 10−15 at at−1), comparable to previously reported 36Cl-to-Cl ratios of deep formation waters and old groundwaters. In addition, 36Cl-to-Cl ratios in atacamite correlate with U and Th concentration in the host rocks but are independent from distance to
the ocean. This trend supports an interpretation of the low 36Cl-to-Cl ratios in atacamite as representing subsurface production of fissiogenic 36Cl in secular equilibrium with the solutions involved in atacamite formation. Therefore, 36Cl in atacamite strongly suggest that the chlorine in saline waters related to atacamite formation is old (>1.5 Ma) but that
atacamite formation occurred more recently (<1.5 Ma) than suggested in previous interpretations. Our data provide new constraints
on the origin of atacamite in Cu deposits from the Atacama Desert and support the recent notion that the formation of atacamite
in hyperarid climates such as the Atacama Desert is an ongoing process that has occurred intermittently since the onset of
hyperaridity. 相似文献
962.
André Medeiros de Andrade Jorge Arigony-Neto Ulisses Franz Bremer Roberto Ferreira Machado Michel Alice César Fassoni-Andrade Carlos Ernesto Goncalves Reynaud Schaefer 《国际地球制图》2016,31(7):803-812
The climate change phenomena have been influencing terrestrial and glacial ecosystems around the planet. Maritime Antarctica is especially sensitive to these climate variations and over the last 50 years increasing global air temperatures have caused extensive glacial retreat. The objective of this study is to evaluate the potential use of the SAR technology in monitoring the surface dynamics of the Potter Peninsula, King George Island, maritime Antarctica. An image generated by the SAR satellite COSMO-SkyMed, obtained on 2 February 2011, was used to extract the backscattering values of targets on the surface for further processing and classification, using a supervised statistic classifier of maximum likelihood for the determination of the surface classes. The average backscattering of water bodies presented high similarity, which made its separation unattainable. On the other hand, the surface classes’ bare ice and wet snow over the glacier presented distinct average backscattering values, which allowed an efficient and precise classification using only this parameter. The classification process showed satisfactory results for periglacial environments, presenting high fidelity to the field data. 相似文献
963.
Fatal landslides in Europe 总被引:4,自引:3,他引:1
Ubydul Haque Philipp Blum Paula F. da Silva Peter Andersen Jürgen Pilz Sergey R. Chalov Jean-Philippe Malet Mateja Jemec Auflič Norina Andres Eleftheria Poyiadji Pedro C. Lamas Wenyi Zhang Igor Peshevski Halldór G. Pétursson Tayfun Kurt Nikolai Dobrev Juan Carlos García-Davalillo Matina Halkia Stefano Ferri George Gaprindashvili Johanna Engström David Keellings 《Landslides》2016,13(6):1545-1554
Landslides are a major hazard causing human and large economic losses worldwide. However, the quantification of fatalities and casualties is highly underestimated and incomplete, thus, the estimation of landslide risk is rather ambitious. Hence, a spatio-temporal distribution of deadly landslides is presented for 27 European countries over the last 20 years (1995–2014). Catastrophic landslides are widely distributed throughout Europe, however, with a great concentration in mountainous areas. In the studied period, a total of 1370 deaths and 784 injuries were reported resulting from 476 landslides. Turkey showed the highest fatalities with 335. An increasing trend of fatal landslides is observed, with a pronounced number of fatalities in the latest period from 2008 to 2014. The latter are mostly triggered by natural extreme events such as storms (i.e., heavy rainfall), earthquakes, and floods and only minor by human activities, such as mining and excavation works. Average economic loss per year in Europe is approximately 4.7 billion Euros. This study serves as baseline information for further risk mapping by integrating deadly landslide locations, local land use data, and will therefore help countries to protect human lives and property. 相似文献
964.
G. Ross Heath David K. Rea Gordon Ness R. Dale Pillsbury Thomas M. Beasley Carlos Lopez Daniel M. Talbert 《Environmental Geology》1984,6(4):189-199
Based on criteria developed by the international Atomic Energy Agency (IAEA), potential disposal sites for defueled, decommissioned
nuclear submarines appear to exist in deep water south of the Mendocino Fracture Zone within 200 nautical miles of the United
States Oceanographic measurements in the water column and at the sea floor in a study area (W-N) at 39 5°N, 127 5°W will allow
the operational and radiological consequences of deep-sea disposal to be compared with land burial of old submarines. The
W-N studies also are yielding new data that will provide insights to the deposition and early diagenesis of distal hemipelagic
sediments
Royalty-free reproduction of this article by the U S Government or by the authors for U S. Government purposes is permitted. 相似文献
965.
Mesozoic and Cenozoic volcanism in the Central Andes occurs near the boundary of convergent oceanic and continental lithospheric plates. The rocks show a chemical and temporal zonation with respect to the present Chile-Peru trench. It is inferred that the geometry of the subduction zone has not changed in the last 190 m.y.; the continental crust during Jurassic time in northern Chile may have been between 15 and 27 km thick. 相似文献
966.
A critical, textbook-like review of the generalized modal superposition method of evaluating the dynamic response of nonclassically damped linear systems is presented, which it is hoped will increase the attractiveness of the method to structural engineers and its application in structural engineering practice and research. Special attention is given to identifying the physical significance of the various elements of the solution and to simplifying its implementation. It is shown that the displacements of a non-classically damped n-degree-of-freedom system may be expressed as a linear combination of the displacements and velocities of n similarly excited single-degree-of-freedom systems, and that once the natural frequencies of vibration of the system have been determined, its response to an arbitrary excitation may be computed with only minimal computational effort beyond that required for the analysis of a classically damped system of the same size. The concepts involved are illustrated by a series of examples, and comprehensive numerical data for a three-degree-of-freedom system are presented which elucidate the effects of several important parameters. The exact solutions for the system are also compared over a wide range of conditions with those computed approximately considering the system to be classically damped, and the interrelationship of two sets of solutions is discussed. 相似文献
967.
Carlos E. Mendoza 《Mathematical Geosciences》1986,18(3):307-322
Data, each consisting of a unit vector and a position, are modeled as a smooth unit vector field plus random directional errors; the smooth unit vector field is estimated by fitting a spline to observations. The estimate is nonlinear; it is obtained with an iterative procedure in which, at each step, a least-squares smoothing spline is fitted to a set of pseudovalues. The resulting estimate is exemplified with a data set extracted from the literature in geology. The proposed estimate is compared, using the same data set with that obtained through suggestions of other authors, and is found to have attractive qualities. The use of plots of the resulting estimate to find the appropriate value of the smoothing parameter is emphasized throughout. 相似文献
968.
969.
970.
A. Carlos P. Borrero Jose Luis H. Naranjo 《Journal of Volcanology and Geothermal Research》1990,41(1-4)
The Upper Pliocene to Pleistocene Casabianca Formation is an assemblage of coarse-grained volcanogenic sediments derived from the Ruiz-Cerro Bravo volcanic axis, which were deposited on the west and east flanks of the middle Colombian Central Cordillera (5°–5°30′ N Lat.; 74°30′–76° W Long.).Facies assemblages, paleocurrent data, and geomorphic expression define four depositional settings: (1) an alluvial fan with debris-flow lobes represented by the Manizales fan in the western sector and the Fresno fan in the eastern sector, characterized by the facies assemblage of Gms, Gp and Gt; (2) valley fill deposits represented by the Arauca section at the west sector, characterized by the facies assemblage of Gms and Gi; (3) deposits produced by the diversion of the debris-flow and hyperconcentrated flood-flow deposits from the main channels into narrow effluent channels; represented by the Delgaditas and Manzanares-Marquetalia sections, in the eastern sector and characterized by the facies assemblage Gms and Gm(a); and (4) lateral accretion in gravelly, medium to high-sinuosity rivers, represented by the Casabianca-Villa Hermosa, Palo Cabildo-Falan, Lagunillas and Guali sections of the eastern sector, characterized by the facies assemblage Gms, Gp and Gt.Casabianca Formation deposition records the response of a semi-arid to tropical fluvial system to large, volcanism-induced sediment loads. 相似文献