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51.
Perrine Paquereau-Lebti Michel Fornari Pierrick Roperch Jean-Claude Thouret Orlando Macedo 《Bulletin of Volcanology》2008,70(8):977-997
40Ar/39Ar ages and paleomagnetic correlations using characteristic remanent magnetizations (ChRM) show that two main ignimbrite sheets
were deposited at 4.86 ± 0.07 Ma (La Joya Ignimbrite: LJI) and at 1.63 ± 0.07 Ma (Arequipa Airport Ignimbrite: AAI) in the
Arequipa area, southern Peru. The AAI is a 20–100 m-thick ignimbrite that fills in the Arequipa depression to the west of
the city of Arequipa. The AAI is made up of two cooling units: an underlying white unit and an overlying weakly consolidated
pink unit. Radiometric data provide the same age for the two units. As both units record exactly the same well-defined paleomagnetic
direction (16 sites in the white unit of AAI: Dec = 173.7; Inc = 31.2; α95 = 0.7; k = 2749; and 10 sites in the pink unit of AAI; Dec = 173.6; Inc = 30.3; α95 = 1.2; k = 1634), showing no evidence of secular variation, the time gap between emplacement of the two units is unlikely to exceed
a few years. The >50 m thick well-consolidated white underlying unit of the Arequipa airport ignimbrite provides a very specific
magnetic zonation with low magnetic susceptibilities, high coercivities and unblocking temperatures of NRM above 580°C indicating
a Ti-poor titanohematite signature. The Anisotropy of Magnetic Susceptibility (AMS) is strongly enhanced in this layer with
anisotropy values up to 1.25. The fabric delineated by AMS was not recognized neither in the field nor in thin sections, because
most of the AAI consists in a massive and isotrope deposit with no visible textural fabric. Pumices deformation due to welding
is only observed at the base of the thickest sections. AMS within the AAI ignimbrite show a very well defined pattern of apparent
imbrications correlated to the paleotopography, with planes of foliation and lineation dipping often at more than 20° toward
the expected vent, buried beneath the Nevado Chachani volcanic complex. In contrast with the relatively small extent of the
thick AAI, the La Joya ignimbrite covers large areas from the Altipano down the Piedmont. Ti-poor titanomagnetites are the
dominant magnetic carriers and AMS values are generally lower than 1.05. Magnetic foliations are sub horizontal and lineations
directions are scattered in the LJI. The AMS fabrics are probably controlled by post-depositional compaction and welding of
the deposit rather than transport dynamics.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
52.
O. Petruk G. Dubner G. Castelletti F. Bocchino D. Iakubovskyi M. G. F. Kirsch M. Miceli S. Orlando I. Telezhinsky 《Monthly notices of the Royal Astronomical Society》2009,393(3):1034-1040
A number of important processes taking place around strong shocks in supernova remnants (SNRs) depend on the shock obliquity. The measured synchrotron flux is a function of the aspect angle between interstellar magnetic field (ISMF) and the line of sight. Thus, a model of non-thermal emission from SNRs should account for the orientation of the ambient magnetic field. We develop a new method for the estimation of the aspect angle, based on the comparison between observed and synthesized radio maps of SNRs, making different assumptions about the dependence of electron injection efficiency on the shock obliquity. The method uses the azimuthal profile of radio surface brightness as a probe for orientation of ambient magnetic field because it is almost insensitive to the downstream distribution of magnetic field and emitting electrons. We apply our method to a new radio image of SN 1006 produced on the basis of archival Very Large Array and Parkes data. The image recovers emission from all spatial structures with angular scales from a few arcsec to 15 arcmin. We explore different models of injection efficiency and find the following best-fitting values for the aspect angle of SN 1006: φo = 70o ± 4.2o if the injection is isotropic, φo = 64o ± 2.8o for quasi-perpendicular injection (SNR has an equatorial belt in both cases) and φo = 11o ± 0.8o for quasi-parallel injection (polar-cap model of SNR). In the last case, SN 1006 is expected to have a centrally peaked morphology contrary to what is observed. Therefore, our analysis provides some indication against the quasi-parallel injection model. 相似文献
53.
Amy L. Rechenmacher Sara Abedi Olivier Chupin Andr��s D. Orlando 《Acta Geotechnica》2011,6(4):205-217
Within shear bands in sands, deformation is largely non-affine, stemming primarily from buckling of well-known force chains
and also from vortex-like structures. In the spirit of current trends toward multiscale modeling, understanding the links
between these mesoscale deformational entities and corresponding macroscale response will form the basis for the next generation
of sand behavioral models and may also aid in efforts to understand jamming–unjamming transitions in dense granular flows
in general. Experimental methods to quantify and characterize such subscale kinematics, in particular in real sands, will
play critical roles in these efforts. Digital Image Correlation (DIC) is a fast growing experimental technique to nondestructively
measure surface displacements from digital images. Here, DIC has been employed to identify and characterize the development
of vortex structures inside shear bands formed in dense sands during plane strain compression. A rigorous assessment of the
DIC method has been performed, in particular for subscale behavioral characterization in unbonded granular solids, and guidelines
are offered for accurate implementation. While DIC systematically overestimates shear band thickness, a methodology has been
devised to compensate for this overestimation. Shear band thickness for four different uniform sands were found to range between
6 and 9 grain diameters, and for a well-graded sand between 8 and 9.5 grain diameters. These determinations agree with visual
inspections of grain kinematics from the image data, as well as recent theoretical predictions. 相似文献
54.
Environmental fate of fungicides and other current-use pesticides in a central California estuary 总被引:2,自引:0,他引:2
Kelly L. Smalling Kathryn M. Kuivila James L. Orlando Bryn M. Phillips Brian S. Anderson Katie Siegler John W. Hunt Mary Hamilton 《Marine pollution bulletin》2013
The current study documents the fate of current-use pesticides in an agriculturally-dominated central California coastal estuary by focusing on the occurrence in water, sediment and tissue of resident aquatic organisms. Three fungicides (azoxystrobin, boscalid, and pyraclostrobin), one herbicide (propyzamide) and two organophosphate insecticides (chlorpyrifos and diazinon) were detected frequently. Dissolved pesticide concentrations in the estuary corresponded to the timing of application while bed sediment pesticide concentrations correlated with the distance from potential sources. Fungicides and insecticides were detected frequently in fish and invertebrates collected near the mouth of the estuary and the contaminant profiles differed from the sediment and water collected. This is the first study to document the occurrence of many current-use pesticides, including fungicides, in tissue. Limited information is available on the uptake, accumulation and effects of current-use pesticides on non-target organisms. Additional data are needed to understand the impacts of pesticides, especially in small agriculturally-dominated estuaries. 相似文献
55.
56.
Perrine Paquereau Jean-Claude Thouret Gerhard Wörner Michel Fornari Orlando Macedo Pierrick Roperch 《Comptes Rendus Geoscience》2005,337(5):477-486
Four ignimbritic units have filled the Arequipa Basin and outcrop around the Chachani Volcano. (1) The oldest Río Chili ignimbrite is 13.33 Ma old; (2) the most widespread La Joya ignimbrite is 4.9 Ma old; (3) the Arequipa Airport ignimbrite (1.65 Ma) flowed from an area buried beneath Chachani; (4) the Yura Tuffs, 1.02 Ma old, are restricted to the west of Chachani. All are calc-alkaline rhyolites with plagioclase, biotite, quartz, sanidine, and opaques, but the Río Chili and La Joya ignimbrites also contain amphibole. Trace elements of the older ignimbrites reflect stronger crustal influence. To cite this article: P. Paquereau et al., C. R. Geoscience 337 (2005). 相似文献
57.
Measurements of NOx,y were made at Alert, Nunavut, Canada (82.5° N, 62.3° W) during surface layer ozone depletion events. In spring 1998, depletion events were rare and occurred under variable actinic flux, ice fog, and snowfall conditions. NOy changed by less than 10% between normal, partially depleted, and nearly completely depleted ozone air masses. The observation of a diurnal variation in NOx under continuous sunlight supports a source from the snowpack but with rapid conversion to nitrogen reservoirs that are primarily deposited to the surface or airborne ice crystals. It was unclear whether NOx was reduced or enhanced in different stages of the ozone depletion chemistry because of variations in solar and ambient conditions. Because ozone was depleted from 15–20 ppbv to less than 1 ppbv in just over a day in one event it is apparent that the surface source of NOx did not grossly inhibit the removal of ozone. In another case ozone was shown to be destroyed to less than the 0.5 ppbv detection limit of the instrument. However, simple model calculations show that the rate of depletion of ozone and its final steady-state abundance depend sensitively on the strength of the surface source of NOx due to competition from ozone production involving NOx and peroxy radicals. The behavior of the NO/NO2 ratio was qualitatively consistent with enhanced BrO during the period of active ozone destruction. The model is also used to emphasize that the diurnal partitioning of BrOx during ozone depletion events is sensitive to even sub ppbv variations in O3. 相似文献
58.
The origin of thermal waters from the eastern flank of the Dead Sea Rift Valley (western Jordan) 总被引:1,自引:0,他引:1
Bruno Capaccioni Orlando Vaselli Elvio Moretti Franco Tassi Roberto Franchi 《地学学报》2003,15(3):145-154
Thermal waters emerging along the eastern flank of the northernmost part of the Dead Sea Rift Valley close to the Yarmuk river are dilute, Ca–SO4–(HCO3) and Na–Cl water types with measured temperatures of 35–60 °C and estimated teperatures, according to silica solubility, of 60–110 °C. They are fed only by present‐day recharged meteoric waters (Wadi Hasa, Al Himma and North Shuna thermal baths) and by meteoric waters contaminated with saline waters (El Ma'in thermal Bath). Although they have been known for a long time, there is still dispute about their origins and the source of heat. On the basis of new chemical and isotopic analyses, the saline waters could represent residual pockets of groundwater in equilibrium with those filling the Dead Sea depression before the last retreat of Lake Lisan at 17–15 kyr bp or with the ancient seawaters of the Sedom Lagoon in the early Pleistocene, in both cases unaffected by significant evaporation processes but chemically and isotopically modified by water/rock interaction. 相似文献
59.
Alexandre Raphael Cabral Orlando Garcia Rocha Filho Richard David Jones 《Journal of Geochemical Exploration》2008,96(1):69-76
Mercury contents in Precambrian banded iron formation-hosted hematite ores are virtually unknown. In an attempt to provide information on the abundance and distribution of Hg in Fe ore, we present analyses for Hg in samples of high-grade soft hematite ore from Gongo Soco, Minas Gerais, Brazil. Bulk samples contain from < 5 to 25 ppb Hg without obvious correlation with major elements. Granulometric fractions of follow-up samples have amounts of Hg from 6 to 48 ppb and display positive linear correlations with total Mn as MnO (r = 0.87), LOI (r = 0.87) and SiO2 (r = 0.76), as well as a negative linear correlation with total Fe as Fe2O3 (r = − 0.87). The correlations suggest that Hg is associated with a hydrated ferruginous groundmass bearing residual Mn, Al and Si, which replaced gangue minerals in itabirite in the process of formation of the Gongo Soco soft hematite ore. 相似文献
60.
Factors affecting habitat occupancy of fish assemblage in the Gulf of Trieste (Northern Adriatic Sea) 总被引:3,自引:0,他引:3
Species composition, richness and abundance of the fish assemblage were studied over six different inshore macrohabitats in the southern part of the Gulf of Trieste (Northern Adriatic Sea) using the visual counts technique. Fifteen environmental variables were taken into consideration in order to determine microhabitat preferences of fish species, using canonical correspondence analysis and electivity indices. The results suggest that the structure of the fish assemblage in shallow habitats is affected by a large number of interplaying factors. Depth, type of bottom and vegetation cover – incorporating both abiotic and biotic variables – are some of the factors responsible for coastal fish distribution. Microhabitat preferences for 29 fish species are presented in the depth range from 0.5 to 3 m. 相似文献