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Marlon M. Jean John W. Shervais Sung-Hi Choi Samuel B. Mukasa 《Contributions to Mineralogy and Petrology》2010,159(1):113-136
The middle Jurassic Coast Range Ophiolite (CRO) is one of the most important tectonic elements in western California, cropping
out as tectonically dismembered elements that extend 700 km from south to north. The volcanic and plutonic sections are commonly
interpreted to represent a supra-subduction zone (SSZ) ophiolite, but models specifying a mid-ocean ridge origin have also
been proposed. These contrasting interpretations have distinctly different implications for the tectonic evolution of the
western Cordillera in the Jurassic. If an SSZ origin is confirmed, we can use the underlying mantle peridotites to elucidate
melt processes in the mantle wedge above the subduction zone. This study uses laser ablation–inductively coupled plasma–mass
spectrometry (LA–ICP–MS) to study pyroxenes in peridotites from four mantle sections in the CRO. Trace element signatures
of these pyroxenes record magmatic processes characteristic of both mid-ocean ridge and supra-subduction zone settings. Group
A clinopyroxene display enriched REE concentrations [e.g., Gd (0.938–1.663 ppm), Dy (1.79–3.24 ppm), Yb (1.216–2.047 ppm),
and Lu (0.168–0.290 ppm)], compared to Group B and C clinopyroxenes [e.g., Gd (0.048–0.055 ppm), Dy (0.114–0.225 ppm), Yb
(0.128–0.340 ppm), and Lu (0.022–0.05 ppm)]. These patterns are also evident in orthopyroxene. The differences between these
geochemical signatures could be a result of a heterogeneous upper mantle or different degrees of partial melting of the upper
mantle. It will be shown that CRO peridotites were generated through fractional melting. The shapes of REE patterns are consistent
with variable degrees of melting initiated within the garnet stability field. Models call for 3% dry partial melting of MORB-source
asthenosphere in the garnet lherzolite field for abyssal peridotites and 15–20% further partial melting in the spinel lherzolite
field, possibly by hydrous melting for SSZ peridotites. These geochemical variations and occurrence of both styles of melting
regimes within close spatial and temporal association suggest that certain segments of the CRO may represent oceanic lithosphere,
attached to a large-offset transform fault and that east-dipping, proto-Franciscan subduction may have been initiated along
this transform. 相似文献
75.
Aerobic oxidation of mackinawite (FeS) and its environmental implication for arsenic mobilization 总被引:1,自引:0,他引:1
Oxidation of mackinawite (FeS) and concurrent mobilization of arsenic were investigated as a function of pH under oxidizing conditions. At acidic pH, FeS oxidation is mainly initiated by the proton-promoted dissolution, which results in the release of Fe(II) and sulfide in the solution. While most of dissolved sulfide is volatilized before being oxidized, dissolved Fe(II) is oxidized into green rust-like precipitates and goethite (α-FeOOH). At basic pH, the development of Fe(III) (oxyhydr)oxide coating on the FeS surface inhibits the solution-phase oxidation following FeS dissolution. Instead, FeS is mostly oxidized into lepidocrocite (γ-FeOOH) via the surface-mediated oxidation without dissolution. At neutral pH, FeS is oxidized via both the solution-phase oxidation following FeS dissolution and the surface-mediated oxidation mechanisms. The mobilization of arsenic during FeS oxidation is strongly affected by FeS oxidation mechanisms. At acidic pH (and to some extent at neutral pH), the rapid FeS dissolution and the slow precipitation of Fe (oxyhydr)oxides results in arsenic accumulation in water. In contrast, the surface-mediated oxidation of FeS at basic pH leads to the direct formation of Fe (oxyhydr)oxides, which provides effective adsorbents for As under oxic conditions. At acidic and neutral pH, the solution-phase oxidation of dissolved Fe(II) accelerates the oxidation of the less adsorbing As(III) to the more adsorbing As(V). This study reveals that the oxidative mobilization of As may be a significant pathway for arsenic enrichment of porewaters in sulfidic sediments. 相似文献
76.
Y. Thomas He Arthur G. Fitzmaurice Azra Bilgin Sunkyung Choi Peggy O’Day John Horst James Harrington H. James Reisinger David R. Burris Janet G. Hering 《Applied Geochemistry》2010
The behavior of As in the subsurface environment was examined along a transect of groundwater monitoring wells at a Superfund site, where enhanced reductive dechlorination (ERD) is being used for the remediation of groundwater contaminated with chlorinated solvents. The transect was installed parallel to the groundwater flow direction through the treatment area. The ERD technology involves the injection of organic C (OC) to stimulate in situ microbial dechlorination processes. A secondary effect of the ERD treatment at this site, however, is the mobilization of As, as well as Fe and Mn. The concentrations of these elements are low in groundwater collected upgradient of the ERD treatment area, indicating that, in the absence of the injected OC, the As that occurs naturally in the sediment is relatively immobile. Batch experiments conducted using sediments from the site inoculated with an Fe(III)- and As(V)-reducing bacterium and amended with lactate resulted in mobilization of As, Fe and Mn, suggesting that As mobilization in the field is due to microbial processes. 相似文献
77.
Because of the increasing public awareness of the greenhouse effect, geological emissions of methane (GEM) have gained more
attention. The Intergovernmental Panel on Climate Change included GEM in the natural sources of methane category in the Fourth
Assessment Report in 2007. The methane flux from mud volcanoes (MVs) is the second leading source within GEM. However, given
that gas flux from MVs has been measured directly only in Sicily and Azerbaijan, the global methane estimation is still a
conservative assumption based on limited data. The behavior of MV activities is seldom reported. This study attempts to estimate
annual methane emissions through MVs by using a video recorder to record MV activities along the Chishan Fault and determining
the bubble size and flux rate of each MV. Observation results, after a 1 year observation period, indicate that the annual
emissions of the 19 MVs along the Chishan Fault are 0.1–0.2% of the global methane flux from MVs, highlighting that the methane
emission from these MVs should not be neglected. In addition, the continuous monitoring of a particular MV disclosed periodic
characteristics of MV activities. These results manifest the spatial and temporal variations of MV activities along the Chishan
Fault. The spatial variations are related to the extensional kinematics of the Chishan fault, while the temporal variation
relates to the earth-tide-related MV activities. The estimated annual methane emissions from the study are far more than those
of previous studies and are still considered conservative. Results of this study may provide valuable information for researchers
attempting to estimate the quantity of GEM. 相似文献
78.
Geological and geotechnical aspects of underground coal mining methods within Australia 总被引:1,自引:1,他引:0
B. Scott P. G. Ranjtih S. K. Choi Manoj Khandelwal 《Environmental Earth Sciences》2010,60(5):1007-1019
About one quarter of the coal produced in Australia is by underground mining methods. The most commonly used underground coal
mining methods in Australia are longwall, and room and pillar. This paper provides a detailed review of the two methods, including
their advantages and disadvantages, the major geotechnical and operational issues, and the factors that need to be considered
regarding their choice, including the varying geological and geotechnical conditions suited to a particular method. Factors
and issues such as capital cost, productivity, recovery, versatility and mine safety associated with the two methods are discussed
and compared. The major advantages of the longwall mining method include its suitability for mining at greater depth, higher
recovery, and higher production rate compared to room and pillar. The main disadvantages of the room and pillar method are
the higher risks of roof and pillar collapse, higher capital costs incurred as well as lower recovery rate. 相似文献
79.
Annual variation in the amount and composition of waste deposited in the Gimpo #2 landfill, the largest landfill around Seoul, Korea, is reviewed, and the stability of the same landfill is analyzed during waste disposal. For the stability analysis, three empirical stability prediction methods, i.e., linear stability, displacement velocity, and curve stability methods, are used to analyze field-measured settlement and horizontal displacement data. The analysis indicated that national waste management policy has greatly influenced the annual variation in the amount and composition of waste deposited in the landfill. Continuous measurement of geotechnical data and the use of stability analysis based on these data are necessary for landfills on seashore clay foundation. Stability of the landfill must be examined with various methods to ensure accurate determination of its stability. 相似文献
80.
Byung Sun Lee Sung-Ho Song Jin Sung Kim Jae Yeon Um Kyoungphile Nam 《Environmental Earth Sciences》2014,71(4):1521-1532
This study was conducted to identify the availability of coastal groundwater discharge (CGD), subsurface fluids flowing from inland through the coastal area to sea, as an alternative water resource for a large-scale reclaimed land. The behaviors of stable isotopes indicated that groundwater originated from inland precipitation and traveled as CGD along the coast line. Most of the groundwater samples collected from domestic wells installed along the old coast line were considered to be relatively fresh from the correlation analysis among chemical constituents. The average electrical conductivity (EC) values of the samples were identified as averaging 1,125–1,297 μS cm?1, corresponding to appropriate crop growth. A weathered-rock layer in a small catchment within the reclaimed land was proved to be a main CGD pathway, with electrical resistivity anomalies ranging from 7 to 14 Ω m. Five monitoring wells were placed in this catchment to delineate the occurrence of CGD. Long-term vertical EC profiling results for the monitoring wells indicated that CGD occurs within a depth of 30 m below the ground surface. Annual monitoring data for groundwater level and EC demonstrated that the water quality of CGD was improved by introducing fresh terrestrial groundwater. A remarkable improvement in water quality (EC decrease of 900–1,600 μS cm?1) of CGD was observed during the saline water pumping test that explains how CGD could be an alternative water resource for the reclaimed land. 相似文献