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61.
Katy Mee Jennie S. Gilbert David W. McGarvie José A. Naranjo Malcolm S. Pringle 《Bulletin of Volcanology》2009,71(8):933-952
Nevados de Chillán Volcanic Complex, central Chile, has been active for at least 640 ka—a period spanning a number of glacial
and interglacial periods. Geologic mapping, radiometric dating and geochemical analysis have identified six new volcanic units
and produced four new 40Ar/39Ar ages for Cerro Blanco, the northern subcomplex of Nevados de Chillán volcano. Compositions range from dacite to basaltic-andesite
and a new geologic map is presented. Examination of lava fracture structures on both newly mapped lavas and those mapped during
previous studies has enabled interpretations of former eruptive environments. Palaeoenvironment reconstructions, combined
with 40Ar/39Ar ages and comparison with the marine oxygen isotope record, show that at least three phases of volcanic activity have occurred
during the evolution of Cerro Blanco: (1) a constructive, pre-caldera collapse period; (2) a period of caldera formation and
collapse; and (3) a constructive period of dome growth forming the modern day volcanic centre. This style of volcanic evolution,
whereby large-scale caldera collapse is followed by growth of a new stratocone is common at Andean volcanoes. 相似文献
62.
63.
John E. Hathaway Richard O. Gilbert John E. Wilson Brent A. Pulsipher 《Stochastic Environmental Research and Risk Assessment (SERRA)》2009,23(2):253-261
After site clean-up teams have removed all of what they believe to be UXO within a specific impact area, statistical compliance
sampling is a possible method for verifying with a specified probability that this area has been cleaned to specifications.
Schilling [J Qual Technol 10(2):47–51, 1978, Acceptance sampling in quality control. Marcel Dekker, Inc., New York, 1982] developed a compliance sampling methodology based on the hypergeometric distribution. Bowen and Bennett (1987) also use compliance sampling where they provide an approximation for estimating the number of samples (n) required to state with desired probability that the entire population of sample units (N, where n < N) are in compliance with cleanup goals. This article describes two methods (anomaly and transect) for applying the Schilling
[J Qual Technol 10(2):47–51, 1978, Acceptance sampling in quality control. Marcel Dekker, Inc., New York, 1982] compliance sampling method to military training sites. After describing these methods, a simulation study is presented which
demonstrates the performance of transect compliance sampling calculations based on varied degrees of clustered UXO within
a specific impact area and different types of sampling routines. 相似文献
64.
65.
66.
Amir?NafiEmail author Eric?Crastes Rehan?Sadiq Denis?Gilbert Olivier?Piller 《Stochastic Environmental Research and Risk Assessment (SERRA)》2018,32(2):527-544
Performing a comprehensive risk analysis is primordial to ensure a reliable and sustainable water supply. Though the general framework of risk analysis is well established, specific adaptation seems needed for systems such as water distribution networks (WDN). Understanding of vulnerabilities of WDN against deliberate contamination and consumers’ sensitivity against contaminated water use is very vital to inform decision-maker. This paper presents an innovative step-by-step methodology for developing comprehensive indicators to perform sensitivity, vulnerability and criticality analyses in case of absence of early warning system (EWS). The assessment and the aggregation of these indicators with specific fuzzy operators allow identifying the most critical points in a WDN. Intentional intrusion of contaminants at these points can potentially harm both the consumers as well as water infrastructure. The implementation of the developed methodology has been demonstrated through a case study of a French WDN unequipped with sensors. 相似文献
67.
Ship noise received on a horizontal array towed behind the ship is shown to be useful as a potentially diagnostic tool for estimating local acoustic bottom properties. In numerical simulations, tow-ship noise which bounces off the bottom is processed on a beamformer that shows the arrival angles; the beamformer output is readily interpreted by relating it to the Green's function of the acoustic wave equation. Simple signal processing is shown to be sufficient to extract the propagation angles of the "trapped" (i.e., propagating) modes of the acoustic waveguide. By relating the trapped modes to a basic geophysical model of the bottom, one can predict acoustic-propagation conditions for a particular bottom-interacting ocean acoustic environment. 相似文献
68.
Verónica Oliveros Dania Tristá-Aguilera Gilbert Féraud Diego Morata Luis Aguirre Shoji Kojima Fernando Ferraris 《Mineralium Deposita》2008,43(1):61-78
The Michilla mining district comprises one of the most important stratabound and breccia-style copper deposits of the Coastal
Cordillera of northern Chile, hosted by the Middle Jurassic volcanic rocks of the La Negra Formation. 40Ar/39Ar analyses carried out on igneous and alteration minerals from volcanic and plutonic rocks in the district allow a chronological
sequence of several magmatic and alteration events of the district to be established. The first event was the extrusion of
a thick lava series of the La Negra Formation, dated at 159.9 ± 1.0 Ma (2σ) from the upper part of the series. A contemporaneous intrusion is dated at 159.6 ± 1.1 Ma, and later intrusive events are
dated at 145.5 ± 2.8 and 137.4 ± 1.1 Ma, respectively. Analyzed alteration minerals such as adularia, sericite, and actinolite
apparently give valid 40Ar/39Ar plateau and miniplateau ages. They indicate the occurrence of several alteration events at ca. 160–163, 154–157, 143–148,
and 135–137 Ma. The first alteration event, being partly contemporaneous with volcanic and plutonic rocks, was probably produced
in a high thermal gradient environment. The later events may be related either to a regional low-grade hydrothermal alteration/metamorphism
process or to plutonic intrusions. The Cu mineralization of the Michilla district is robustly bracketed between 163.6 ± 1.9
and 137.4 ± 1.1 Ma, corresponding to dating of actinolite coexisting with early-stage chalcocite and a postmineralization
barren dyke, respectively. More precisely, the association of small intrusives (a dated stock from the Michilla district)
with Cu mineralization in the region strongly suggests that the main Michilla ore deposit is related to a magmatic/hydrothermal
event that occurred between 157.4 ± 3.6 and 163.5 ± 1.9 Ma, contemporaneous or shortly after the extrusion of the volcanic
sequence. This age is in agreement with the Re–Os age of 159 ± 16 Ma obtained from the mineralization itself (Tristá-Aguilera
et al., Miner Depos, 41:99–105,2006). 相似文献
69.
70.
Pb isotope data, major and trace element compositions, fission track and synchrotron X-ray fluorescence analyses are presented
for staurolites from nine pelitic schists in the continental United States to evaluate their potential use in U-Pb geochronology.
Seven U-Pb analyses from Lanzirotti and Hanson (1995) are reexamined with respect to this additional data which was not available
at the time. These data are then compared to 21 new U-Pb analyses of staurolite of varying composition from a variety of localities.
The primary goals of this study are to: (1) evaluate the variability in U and Pb abundance and U/Pb ratio in staurolites of
varying composition; (2) constrain how much of the measured U and Pb is derived from radiogenic solid inclusions such as monazite
and zircon; (3) constrain how much of the measured U and Pb is derived from staurolite itself and evaluate any possible correlation
of U and Pb abundance and U/Pb ratio to major element composition; (4) place preliminary constraints on closure temperature
to Pb diffusion in staurolite; (5) evaluate how meaningful U-Pb ages can better be calculated for the low U/Pb ratio minerals.
In the staurolite fractions analyzed U abundances range from 0.2 to 24.9 ppm, Pb from 0.13 to 2.41 ppm, the 238U/204Pb ratios vary from 135 to 9447, and the 206Pb/204Pb ratios from 23 to 623. For many of the fractions analyzed precise U-Pb ages can be calculated (±10 Ma or better) that appear
to be consistent with available age constraints on the time of peak metamorphism. Mass balance calculations, fission track
analysis, and synchrotron X-ray fluorescence trace element mapping show that although radiogenic inclusions are almost always
present in large staurolite porphyroblasts, it is difficult for inclusions to account for the measured Pb isotopic compositions.
It is also demonstrated that the U-Pb ages calculated for staurolites from Connecticut are at least 20 Ma older than nearby
Rb-Sr muscovite and 40Ar-39Ar hornblende ages. This is consistent with staurolite having a closure temperature to U and Pb diffusion significantly higher
than 500 °C.
Received: 14 July 1995 / Accepted: 16 May 1997 相似文献