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291.
Antonio Pedrera Jesús Galindo-Zaldívar Alejandro Tello Carlos Marín-Lechado 《Journal of Geodynamics》2010,49(5):271-286
Among the classical minor structural associations on the termination of transcurrent faults are horsetail splays formed by reverse, normal or strike-slip faults developing duplexes. However, temporal and spatial coexistence of contractional and extensional structures is very rarely documented. We discuss the relationships of contractional and extensional structures and associated sedimentary depocenters at the termination of a major strike-slip fault in the Eastern Betic Cordillera. Field mapping, kinematic fault analysis, paleostress determination and gravity prospecting in the Huércal-Overa Basin, at the southern termination of the NE–SW Alhama de Murcia transcurrent fault (AMF), are used to establish the relationships of tectonic structures and associated sedimentary depocenters. Here, ENE–WSW and WNW–ESE folds interact with two sets of normal faults having the same orientation as well as ENE–WSW reverse faults. Progressive unconformities associated with folds reveal that the beginning of the AMF activity occurred in the Tortonian. The folds progressively grew and rotated from ENE–WSW up to WNW–ESE close to the transcurrent fault. We propose that the development of the normal faults developed during short-term episodes characterized by vertical major stress axis and are, in turn, related to gravitational instability linked to the thickening of a crust relatively hot at depth. This setting may have become predominant in between the main activity, compressive pulses along transcurrent faults. 相似文献
292.
Jos Luis Cervantes-Rodríguez Alejandro Vazdekis Jordi Cepa 《New Astronomy Reviews》2006,49(10-12):670
We present the modelling of new indicators for old and intermediate age stellar populations based on the absorption features of Mg λ 5175 Å, Fe λ 4383 Å, and Hβ λ 5270, 4860 Å. Spectral models of stellar populations are convolved with the responses of the tunable filters of OSIRIS-GTC to provide photometric indexes with great abilities to separate age and metallicity effects. The new indexes allow us to obtain 2D maps of these features on the basis of a photometric approach and are built up to unreveal most relevant stellar population parameters. 相似文献
293.
Kinematics of the Iberia–Maghreb plate contact from seismic moment tensors and GPS observations 总被引:2,自引:0,他引:2
Daniel Stich Enrico Serpelloni Flor de Lis Mancilla Jose Morales 《Tectonophysics》2006,426(3-4):295-317
The Iberian Peninsula and the Maghreb experience moderate earthquake activity and oblique, NW–SE convergence between Africa and Eurasia at a rate of 5 mm/yr. Coeval extension in the Alboran Basin and a N35°E trending band of active, left-lateral shear deformation in the Alboran–Betic region are not straightforward to understand in the context of regional shortening, and evidence complexity of deformation at the plate contact. We estimate 86 seismic moment tensors (MW 3.3 to 6.9) from time domain inversion of near-regional waveforms in an intermediate period band. Those and previous moment tensors are used to describe regional faulting style and calculate average stress tensors. The solutions associated to the Trans-Alboran shear zone show predominantly strike-slip faulting, and indicate a clockwise rotation of the largest principal stress orientation compared to the regional convergence direction (σ1 at N350°E). At the N-Algerian and SW-Iberian margins, reverse faulting solutions dominate, corresponding to N350°E and N310°E compression, respectively. Over most of the Betic range and intraplate Iberia, we observe predominately normal faulting, and WSW–ENE extension (σ3 at N240°E). From GPS observations we estimate that more than 3 mm/yr of African (Nubian)–Eurasian plate convergence are currently accommodated at the N-Algerian margin, 2 mm/yr in the Moroccan Atlas, and 2 mm/yr at the SW-Iberian margin. 2 mm/yr is a reasonable estimate for convergence within the Alboran region, while Alboran extension can be quantified as 2.5 mm/yr along the stretching direction (N240°E). Superposition of both motions explains the observed left-lateral transtensional regime in the Trans-Alboran shear zone. Two potential driving mechanisms of differential motion of the Alboran–Betic–Gibraltar domain may coexist in the region: a secondary stress source other than plate convergence, related to regional-scale dynamic processes in the upper mantle of the Alboran region, as well as drag from the continental-scale motion of the Nubian plate along the southern limit of the region. In the Atlantic Ocean, the 3.5 mm/yr, westward motion of the Gibraltar Arc relative to intraplate Iberia can be accommodated at the transpressive SW-Iberian margin, while available GPS observations do not support an active subduction process in this area. 相似文献
294.
Martin Reich Carlos Palacios Gabriel Vargas Shangde Luo Eion M. Cameron Matthew I. Leybourne Miguel A. Parada Alejandro Zúñiga Cheng-Feng You 《Mineralium Deposita》2009,44(5):497-504
Supergene enrichment of Cu deposits in the Atacama Desert has played a critical role in making this the prime Cu-producing
province of the world. Previously, this has been believed to have occurred exclusively over a long period from the middle
Eocene to the late Miocene, which ended when climatic conditions changed from arid to hyperarid. Here, we report U-series
disequilibrium ages in atacamite-bearing supergene assemblages that provide a new conceptualization on both the supergene
enrichment process and the onset of extreme hyperaridity in the Atacama Desert. 230Th–234U ages of gypsum intergrown with atacamite in supergene veins from Cu deposits cluster at ~240 ka (Chuquicamata), 130 ka (Mantos
Blancos, Spence), and 80 ka (Mantos de la Luna, Michilla). When coupled with previous data, these results indicate that supergene
enrichment of Cu deposits did not cease after the onset of hyperaridity. We propose that supergene enrichment in the Atacama
region developed in two main stages. The main phase, caused by downward circulation of meteoric waters in a semi-arid setting,
was active from 45 until ~9 Ma, with a last pulse ca. 5 Ma in the southern Atacama Desert. During this phase, atacamite-bearing
supergene assemblages were not preserved because atacamite requires saline water for its formation and rapidly dissolves when
contacted by meteoric water. This was followed by a second stage starting at ~2–1.5 Ma and continuing until at least the late
Pleistocene, when deep formation waters derived from the basement passed up through and modified the pre-existing supergene
Cu oxide minerals. Atacamite has then been preserved in the prevailing hyperarid climate. 相似文献
295.
In the area surrounding the El Teniente giant porphyry copper deposit, eight soil sites were sampled at three depth levels
in the summer 2004. The sites were selected for their theoretical potential of being influenced by past SO2 emissions from the smelter and/or seepage from a now idle tailings impoundment. The soil mineralogy, grain size distribution,
total organic matter contents, major element composition, cation exchange capacity, and Cu, Mo, Pb, Zn, As and SO4
2− concentrations were determined for all samples after nitric acid extraction and separate leaches by ammonium acetate (pH
7) and sodium acetate (pH 5). For water rinses, only Cu could be determined with the analytical set-up used. Cu and SO4
2− enrichment in topsoils was found at six sites either downwind from the smelter or within the combined influence of the smelter
and the tailings impoundment. Both elements were released partially by ammonium and sodium acetate extractions. Due to the
scarce background trace element concentrations of soil and rock outside the immediate mine area, assessment of trace element
mobility for Mo, Zn, Pb and As was difficult. Arsenic was found to be concentrated in soil horizons with high smectite and/or
organic matter contents. Mo appears to be linked to the presence of windblown tailings sediment in the soils. Mobilization
of Mo, Zn, and As for the acetate extractions was minimal or below the detection limits for the AAS technique used. The presence
of windblown tailings is considered to be an additional impact on the soils in the foothills of the El Teniente compound,
together with the potential of acidity surges and Cu mobilization in topsoils after rainfalls. Two sites located at the western
limit of the former SO2 saturated zone with strongly zeolitized soils and underlying rock did not show any Cu or SO4
2− enrichment in the topsoils, and remaining total trace element concentrations were below the known regional background levels. 相似文献
296.
Lucien von Gunten Martin Grosjean Urs Eggenberger Philipp Grob Roberto Urrutia Arturo Morales 《Global and Planetary Change》2009,68(3):198-208
One of the fundamental problems to quantifying past impact of anthropogenic activities is that long series of observational data for pollutant deposition and changes in the nutrient cycling of ecosystems (eutrophication) are often not available. Lake sediments may provide suitable archives to decipher the history of local and regional pollution and eutrophication.Here we provide quantitative high-resolution data for the history of airborne pollutants and eutrophication from sediments of five lakes in Central Chile between ca. AD 1800–2005. We use spheroidal carbonaceous particles (SCPs) from fossil fuel combustion and excess atmospheric Cu deposition from mining activities as a proxy for atmospheric deposition. Organic carbon and nitrogen flux rates to the sediments and C/N ratios are used as a proxy for aquatic primary production and eutrophication.We show that the lake sediment SCP and Cu records are highly consistent and depict in great detail the local and regional history of urban, industrial and transportation history as reported in independent documentary sources and statistics. The pre-industrial and pre-1950 background concentrations (and flux rates) of the substances can be quantified. We can also show that technical measures taken in the early 1980s to trim down Cu emissions from the copper mines reduced the excess atmospheric Cu fallout to the lakes by about 50%.Eutrophication of the lakes did not start before ca. 1980. Prior to that time, warm season temperatures explain most of the variance in TOC and N flux to the sediments. The three dimictic lakes show only moderate eutrophication responses to enhanced N supply (as atmospheric fallout; enrichment factors for TOC and N 1.1–2.6), suggesting that mainly phosphorus controls aquatic primary production. The meromictic lake, where phosphorus recycling is likely, shows the largest response (enrichment factors for TOC and N between 9–20).While all five lakes show overall consistent and similar trends for the pollution history during the 19th and 20th century, there are significant differences in the details of the individual profiles. This suggests that local sources are highly important and the common regional (background) signal is relatively marginal. This is very different from Europe. 相似文献
297.
Alejandro M. Leiva Carlos Bruno Briozzo 《Celestial Mechanics and Dynamical Astronomy》2008,101(3):225-245
Starting from 80 families of low-energy fast periodic transfer orbits in the Earth–Moon planar circular Restricted Three Body
Problem (RTBP), we obtain by analytical continuation 11 periodic orbits and 25 periodic arcs with similar properties in the
Sun–Earth–Moon Quasi-Bicircular Problem (QBCP). A novel and very simple procedure is introduced giving the solar phases at
which to attempt continuation. Detailed numerical results for each periodic orbit and arc found are given, including their
stability parameters and minimal distances to the Earth and Moon. The periods of these orbits are between 2.5 and 5 synodic
months, their energies are among the lowest possible to achieve an Earth–Moon transfer, and they show a diversity of circumlunar
trajectories, making them good candidates for missions requiring repeated passages around the Earth and the Moon with close
approaches to the last. 相似文献
298.
Jaume Bech Magali Suarez Ferran Reverter Pedro Tume Pedro Sánchez Joan Bech Alejandro Lansac 《Journal of Geochemical Exploration》2010
Selenium is an essential trace element in regard to human and other animals' health, but it presents a narrow range of dietary deficiency and toxic excess. Some phosphate rocks are rich in selenium. Furthermore it is necessary to control selenium's and other trace elements’ compositions in the phosphate rocks, because phosphorite ores of different geographical sites are varied, and even ores from the same outcrop can vary substantially in trace element levels. 相似文献
299.
J. L. Justo E. Justo J. M. Azañón P. Durand A. Morales 《Rock Mechanics and Rock Engineering》2010,43(3):287-304
Three-dimensional, elastic and elasto-plastic finite element (FE) programs have permitted calculation of the displacements and the factor of safety (FOS) for the excavation for a tower, 132.70 m high (above foundation) on the island of Tenerife. The tower is supported by a 2 m thick reinforced concrete slab on jointed, vesicular and weathered basalt and scoria. The installation of rod extensometers at different depths below the slab has permitted comparison between measured and calculated displacements and the estimation of in situ deformation modulus. The moduli deduced from the simple empirical equations proposed by Hoek et al. (In: NARMS-TAC, 2002) and Gokceoglu et al. (Int J Rock Mech Min Sci 40:701–710, 2003) as a function of GSI, and Nicholson and Bieniawski (Int J Min Geol Eng 8:181–202, 1990) as a function of RMR, provide an acceptable fit with the measured settlements in this type of rock. Good correlation is also obtained with the empirical equation presented by Verman et al. (Rock Mech Rock Eng 30(3):121–127, 1997) that incorporates the influence of confining stress in the deformation modulus. The FOS obtained from different correlations with geomechanical classifications is within a relatively narrow range. These results increase our confidence in the use of classification schemes to estimate the deformation and stability in jointed rock. 相似文献
300.
Andrea Seelenfreund Mario Pino Michael D. Glascock Carole Sinclaire Pedro Miranda Denisse Pasten Simn Cancino María Ins Dinator Jos Roberto Morales 《Geoarchaeology》2010,25(2):245-263
This paper describes a large obsidian deposit located along the southern banks of Laguna Blanca, on the eastern slope of the Jarellón volcanic caldera near the Chilean–Bolivian border. The obsidian at this site occurs in flows or sheets of deflated black or reddish to brown pebbles, redeposited on the shores of a lake. Blocks of obsidian are only found around the caldera rim. Here we analyze the shape of the obsidian pebbles and their geochemistry, comparing them with previously published data. The results indicate that the geochemical composition of the samples strongly matches previous analyses of obsidian from cultural contexts. This obsidian source was one of the most important sites of obsidian procurement since at least the Formative Period in the Atacama Puna region. © 2010 Wiley Periodicals, Inc. 相似文献