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531.
Variable microstructure of peridotite samples from the southern Mariana Trench: Evidence of a complex tectonic evolution 总被引:2,自引:0,他引:2
Katsuyoshi Michibayashi Miki Tasaka Yasuhiko Ohara Teruaki Ishii Atsushi Okamoto Patricia Fryer 《Tectonophysics》2007,444(1-4):111-118
We retrieved samples of peridotite from a dredge haul (KH92-1-D2) collected during Cruise KH92-1 undertaken by the research vessel (R/V) Hakuho in 1992 at the landward trench slope of the southern Mariana Trench (11°41.16′N, 143°29.62′E; depth 6594–7431 m), which is the deepest ocean in the world. Ten of 30 retrieved samples possessed both a foliation and lineation, as assessed from 46 thin sections of various orientations and observations of hand samples. The samples showed marked variation in microstructure, ranging from coarse (> 5 mm) equigranular and intensely elongated textures to finer (< 1 mm) porphyroclastic and fine-grained equigranular textures. Olivine fabrics also varied among the different samples, with (010)[100] and (010)[001] patterns (termed A- and B-type, respectively) observed in samples with coarse textures and no clear patterns observed in samples with fine textures. Even though the peridotite samples were retrieved from a single dredge site, some contain primary tectonic microstructures and some contain secondary microstructures. Recent bathymetric and topographic analyses indicate that the lithosphere in this region is as thin as 20 km. Such a thin lithosphere may have been intensely deformed, even perhaps in the ductile regime, during fore-arc extension; consequently, the observed variations in microstructure within the peridotite samples probably reflect the complex tectonic evolution of the southern Mariana region. 相似文献
532.
The effect of calcium on aqueous uranium(VI) speciation and adsorption to ferrihydrite and quartz 总被引:2,自引:0,他引:2
Recent studies of uranium(VI) geochemistry have focused on the potentially important role of the aqueous species, CaUO2(CO3)32− and Ca2UO2(CO3)30(aq), on inhibition of microbial reduction and uranium(VI) aqueous speciation in contaminated groundwater. However, to our knowledge, there have been no direct studies of the effects of these species on U(VI) adsorption by mineral phases. The sorption of U(VI) on quartz and ferrihydrite was investigated in NaNO3 solutions equilibrated with either ambient air (430 ppm CO2) or 2% CO2 in the presence of 0, 1.8, or 8.9 mM Ca2+. Under conditions where the Ca2UO2(CO3)30(aq) species predominates U(VI) aqueous speciation, the presence of Ca in solution lowered U(VI) adsorption on quartz from 77% in the absence of Ca to 42% and 10% at Ca concentrations of 1.8 and 8.9 mM, respectively. U(VI) adsorption to ferrihydrite decreased from 83% in the absence of Ca to 57% in the presence of 1.8 mM Ca. Surface complexation model predictions that included the formation constant for aqueous Ca2UO2(CO3)30(aq) accurately simulated the effect of Ca2+ on U(VI) sorption onto quartz and ferrihydrite within the thermodynamic uncertainty of the stability constant value. This study confirms that Ca2+ can have a significant impact on the aqueous speciation of U(VI), and consequently, on the sorption and mobility of U(VI) in aquifers. 相似文献
533.
Remediation of piled foundations against lateral spreading by passive site stabilization technique 总被引:2,自引:0,他引:2
Ahmet Pamuk Patricia M. Gallagher Thomas F. Zimmie 《Soil Dynamics and Earthquake Engineering》2007,27(9):864-874
Physical modeling tests were conducted on pile foundations to measure the seismic performance of a new ground improvement technology, called passive site stabilization, for use on sites susceptible to liquefaction and liquefaction-induced lateral spreading. The method involves the slow injection of a low-viscosity stabilizer in conjunction with the natural groundwater flow. The effectiveness of the treatment using dilute colloidal silica as the stabilizer was tested by two centrifuge models that simulated soil–pile interaction of a 2×2 end-bearing pile group embedded in a multilayer soil deposit of 10-m thickness. The models utilized a laminar box and involved gently inclined soil profiles with and without the applied soil improvement. Response of the pile groups and the lateral spreading behaviors of the treated and untreated soil under a simulated base shaking were investigated and compared. The results showed that treatment with dilute colloidal silica stabilizer minimized permanent lateral deformations and reduced the liquefaction potential of the soil. Significant reductions occurred in the measured pile bending moments and axial forces because the layer treated with dilute colloidal silica did not liquefy. Thus, the technique can be an alternative to traditional methods of ground improvement. 相似文献
534.
Meldrum James R. Brenkert-Smith Hannah Champ Patricia A. Gomez Jamie Byerly Hilary Falk Lilia Barth Christopher M. 《Natural Hazards》2021,106(3):2139-2161
Natural Hazards - Private landowners are important actors in landscape-level wildfire risk management. Accordingly, wildfire programs and policy encourage wildland–urban interface homeowners... 相似文献
535.
Reyes-Carmona Cristina Galve Jorge Pedro Moreno-Sánchez Marcos Riquelme Adrián Ruano Patricia Millares Agustín Teixidó Teresa Sarro Roberto Pérez-Peña José Vicente Barra Anna Ezquerro Pablo López-Vinielles Juan Béjar-Pizarro Marta Azañón José Miguel Monserrat Oriol Mateos Rosa María 《Landslides》2021,18(12):3781-3798
Landslides - When an active landslide is first identified in an artificial reservoir, a comprehensive study has to be quickly conducted to analyse the possible hazard that it may represent to such... 相似文献
536.
Jennifer?M.?GarrisonEmail authorView authors OrcID profile Kenneth?W.?W.?Sims Gene?M.?Yogodzinski Ricardo?D.?Escobar Sean?Scott Patricia?Mothes Minard?L.?Hall Patricio?Ramon 《Contributions to Mineralogy and Petrology》2018,173(1):6
Sumaco Volcano is located in the rear-arc of Ecuador and produces phonolitic alkaline lavas hosting a unique assemblage of minerals including haüyne and titanaugite. The most mafic lavas are picrobasalts that contain titanaugite as the primary mineral phase; the most evolved tephri-phonolite lavas contain titanaugite?+?anorthoclase?+?haüyne. Titanaugite forms at middle to deep crustal pressures, whereas haüyne is only stable at shallow depths in highly oxidizing conditions. The Sumaco mineral assemblages and geochemistry indicate that fractionation of the titanaugite- and haüyne-bearing assemblage took place over a range of pressures from 5 to 25 kbar (14–75 km), with at least 50% of differentiation taking place at shallow crustal levels. Minerals record multiple cycles of recharge and mixing accompanied by an increase in fO2 and sulfur concentration during differentiation. Mantle-like Sr and Nd isotope values (87Sr/86Sr = 0.70406–0.70423; 143Nd/144Nd = 0.512880–0.512913) indicate minimal crustal assimilation. Sumaco’s unique geochemical composition is not observed in the nearby volcanoes Antisana, Pan de Azucar or El Reventador suggesting that its unique magma source is confined to this volcano. The high temperature and sulfate-saturated conditions at shallow depths suggest that magma ascends rapidly to a shallow reservoir where the majority of crystallization and recharge takes place prior to eruption. An important conclusion of this research is that Sumaco does not represent typical rear-arc subduction processes, and caution should be used when using Sumaco as an end-member to evaluate across-arc processes in the Northern Volcanic Zone. 相似文献
537.
William F. Kenney Thomas J. Whitmore David G. Buck Mark Brenner Jason H. Curtis Jian J. Di Patricia L. Kenney Claire L. Schelske 《Journal of Paleolimnology》2014,51(4):515-528
Lake Lochloosa, Florida (USA) recently underwent a shift from macrophyte to phytoplankton dominance, offering us the opportunity to use a whole-basin, mass-balance approach to investigate the influence of phosphorus loading on ecosystem change in a shallow, sub-tropical lake. We analyzed total phosphorus (TP) sedimentation in the basin to improve our understanding of the forcing factor responsible for the recent shift to phytoplankton dominance. We measured 210Pb activity, organic matter (OM), organic carbon (OC) and TP in short sediment cores from 20 locations to develop a comprehensive, whole-basin estimate of recent mass sedimentation rates (MSR) for bulk sediment, OM, OC and TP. The whole-basin sedimentation models provided insights into historic lake processes that were not evident from the limited, historic water quality data. We used Akaike’s Information Criteria to differentiate statistically between constant MSR and exponentially increasing MSR. An eightfold, exponential increase in TP accumulation over the past century provided evidence for the critical role of increased P loading as a forcing factor in the recent shift to phytoplankton dominance. Model results show increased TP retention and decreased TP residence time were in-lake responses to increased TP loading and the shift from macrophyte to phytoplankton dominance in Lake Lochloosa. Comparison of TP loading with TP retention and historic, diatom-inferred limnetic TP concentrations identified the TP loading threshold that was exceeded to trigger the shift to phytoplankton dominance. 相似文献
538.
Gustavo González Bonorino Víctor Rinaldi Liliana del Valle Abascal Patricia Alvarado Gustavo G. Bujalesky Arturo Güell 《Natural Hazards》2012,61(2):337-349
Patagonia, including the island of Tierra del Fuego, lies in southernmost South America at the junction of the South American,
Antarctic, and Scotia tectonic plates. Historical and instrumental records have documented several local earthquakes of damaging
magnitude, posing a threat to the rapidly growing population of 300,000 and the expanding industrial and service infrastructure.
Short and inaccurate instrumental records of local seismic events and a diffuse epicenter distribution not clearly related
to the recognized seismogenic structures have hindered an adequate evaluation of the seismic hazard for this region. To improve
this situation, a paleoseismological study was carried out on two gravelly strandplains on the Atlantic coast of Patagonia.
Surveying combined ground-probing radar, vertical electric sounding, and seismic refraction. Coseismic normal faults buried
beneath the strandplain bodies were revealed and related to the morphology of the strandplains. The faults have probable ages
between 0.9 and 6.4 kyr BP and a recurrence rate of about 1 kyr. The more likely source for these structures is the Magallanes-Fagnano
fault, a continental transform fault that crosses Tierra del Fuego. The distance of more than 300 km from the buried coseismic
structures to the trace of the Magallanes-Fagnano fault argues for high-magnitude earthquake activity on this fault throughout
the Holocene. Urban development on soft glacial and alluvial substrates increases the hazard. 相似文献
539.
Eleonora S. Carol Eduardo E. Kruse Patricia C. Laurencena Adolfo Rojo Marta H. Deluchi 《Environmental Earth Sciences》2012,65(2):421-428
The phreatic aquifer beneath the Pampean plain, in eastern central Argentina, constitutes a relevant source of water supply
in the area. The objective of this work was to assess the significance of the cation exchange processes in the hydrochemical
evolution of this aquifer, based on a study case located in the middle and upper basin of the El Pescado creek. Results indicate
that Ca2+/Na+ exchange is the main process determining the evolution of groundwater from the recharge areas (Ca–HCO3) towards the local discharge areas (Na–HCO3), as well as representing a source of Na+ contribution to the water in the aquifer. This hydrochemical characteristic is central to the identification of local discharge
areas within a plain environment which extends regionally. The ion exchange capacity of these discharge areas has environmental
importance, due to its influence on groundwater quality and potential groundwater uses. These results may be applied to any
aquifer sharing similar hydrogeological characteristics. 相似文献
540.