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排序方式: 共有6523条查询结果,搜索用时 15 毫秒
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An Example of Island-Arc Petrogenesis: Geochemistry and Petrology of the Southern Luzon Arc, Philippines 总被引:7,自引:1,他引:6
DEFANT MARC J.; MAURY REN? C.; RIPLEY EDWARD M.; FEIGENSON MARK D.; JACQUES DARIO 《Journal of Petrology》1991,32(3):455-500
Volcanism throughout the Luzon arc is associated with eastwardsubduction of the South China Sea floor along the Manila Trench.The southern section of the arc, the focus of this study, extendsfrom the Lingayen-Dingalan fault to the small islands just southof Luzon. Two segments appear to exist along this section ofthe arc the northern Bataan and southern Mindoro segments whichare separated by the Macolod Corridor. The volcanic rocks have typical arc phenocryst mineralogies:olivine, clinopyroxene, plagioclase, and titanomagnetite inthe most mafic rocks and clinopyroxene, plagioclase, orthopyroxene,titanomagnetite, ? amphibole in the more felsic samples. Complexzoning, sieve textures, and decoupling of incompatible traceelements suggest that processes such as assimilation have takenplace. The rocks from the study area range from basalts to rhyolitesand show typical calc-alkaline features. The rocks of the MacolodCorridor and Mindoro segment are particularly enriched in largeion lithophile elements (LILE), light rare earth elements (LREE),and radiogenic Sr compared with the Bataan segment. The datafall within the mantle array on Sr-Nd isotopic diagrams andgrade toward higher Sr and lower Nd isotopic values from northto south. A likely source for the volcanics of this study is either amid-ocean ridge basalt (MORB)-type mantle that undergoes higherdegrees of partial melting than regions involved in MORB generationor a previously depleted source. We suggest that the high fieldstrength element (HFSE) anomalies have been derived throughdifferential element partitioning during fluid transport fromthe subducted lithosphere to the mantle wedge. Continental crustal material seems to play a significant roleparticularly in the Macolod Corridor and the Mindoro segment,based on the high LILE, La/Sm ratios, radiogenic Sr isotopes,and 18O values. The Macolod Corridor and the Mindoro segmenthave undergone source contamination by crustal material fromthe North Palawan-Mindoro crustal block either during the collisionof this block with the Manila Trench or by subduction of sedimentsrich in this crustal material. A similar component has alsobeen detected in the Bataan segment but in minor amounts. Thetrace element and isotopic differences between the northernand southern sections of the arc are interpreted in terms ofvariable composition (i. e., variable amounts of a crustal componentintroduced from the Palawan-Mindoro crustal terrain) of themetasomatic fluids released into the source. 相似文献
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Mirta Garrido Fernando Barra Eduardo Domínguez Joaquin Ruiz Victor A. Valencia 《Mineralium Deposita》2008,43(5):591-597
The La Voluntad porphyry Cu–Mo deposit in Neuquén, Argentina, is one of several poorly known porphyry-type deposits of Paleozoic
to Early Jurassic age in the central and southern Andes. Mineralization at La Voluntad is related to a tonalite porphyry from
the Chachil Plutonic Complex that intruded metasedimentary units of the Piedra Santa Complex. Five new Re–Os molybdenite ages
from four samples representing three different vein types (i.e., quartz–molybdenite, quartz–sericite–molybdenite and quartz–sericite–molybdenite
± chalcopyrite–pyrite) are identical within error and were formed between ~312 to ~316 Ma. Rhenium and Os concentrations range
between 34 to 183 ppm and 112 to 599 ppb, respectively. The new Re–Os ages indicate that the main mineralization event at
La Voluntad, associated to sericitic alteration, was emplaced during a time span of 1.7 ± 3.2 Ma and that the deposit is Carboniferous
in age, not Permian as previously thought. La Voluntad is the oldest porphyry copper deposit so far recognized in the Andes
and indicates the presence of an active magmatic arc, with associated porphyry style mineralization, at the proto-Pacific
margin of Gondwana during the Early Pennsylvanian. 相似文献
7.
Unconsolidated sand, gravel and clay deposits near Beihai and in the Leizhou Peninsula in southern China form an unconfined
aquifer, aquitard and a confined aquifer. Water and soil samples were collected from the two aquifers in the coastal Beihai
area for the determination of chemical compositions, minerals and soluble ions. Hydrogeochemical modeling of three flow paths
through the aquitard are carried out using PHREEQC to determine water–rock interactions along the flow paths. The results
indicate that the dissolution of anorthite, fluorite, halite, rhodochrosite and CO2, and precipitation of potash feldspar and kaolinite may be occurring when groundwater leaks through the aquitard from the
unconfined aquifer to the confined aquifer. Cation exchanges between Na and Ca can also happen along the flow paths. 相似文献
8.
The Samborombon Bay wetland is located on the west margin of the Rio de la Plata estuary, in the Province of Buenos Aires,
Argentina. This paper analyses the geological, geomorphologic, soil and vegetation characteristics of the southernmost sector
of this wetland and their influence on surface water and groundwater. The study area presents three hydrologic units: coastal
dunes, sand sheets and coastal plain. Coastal dunes and sand sheets are recharge zones of high permeability with well-drained,
non-saline soils, and a few surface water flows. Changes in the water table are related to rainfall. Groundwater in coastal
dunes is Ca–Mg–HCO3 to Na–HCO3, and of low salinity (590 mg/l). Groundwater in sand sheets is mainly Na–HCO3 with a salinity of about 1,020 mg/l. The coastal plain exhibits medium to low permeability sediments, with submerged saline
soils poorly drained. Groundwater is Na–Cl with a mean salinity of 16,502 mg/l. A surface hydrological network develops in
the coastal plain. Surface water levels near the shoreline are affected by tidal fluctuations; far from the shoreline water
accumulates because of poor drainage. Both sectors have Na–Cl water, but the former is more saline. Human intervention and
sea level rise may affect the wetland severely. 相似文献
9.
Eduardo E. Alonso Sarah M. Springman Charles W. W. Ng 《Geotechnical and Geological Engineering》2008,26(6):817-826
Two large-scale “in situ” demonstration experiments and their instrumentation are described. The first test (FEBEX Experiment)
involves the hydration of a compacted bentonite barrier under the combined effect of an inner source of heat and an outer
water flow from the confining saturated granite rock. In the second case, the progressive de-saturation of Opalinus clay induced
by maintained ventilation of an unlined tunnel is analyzed. The paper shows the performance of different sensors (capacitive
cells, psychrometers, TDR’s) and a comparison of fill behaviour with modelling results. The long term performance of some
instruments could also be evaluated specially in the case of FEBEX test. Capacitive sensors provide relative humidity data
during long transient periods characterised by very large variations of suction within the bentonite. 相似文献
10.
Diel patterns in the chlorophyll a specific absorption coefficient of surface picoplankton, a*pico (γ) (m2·[mg chlorophyll a]−1), were studied at 7 stations under daily cycle of in situ light condition in the western subarctic Pacific and Japan Sea. All the data were normalized by dividing the anomaly with daily averaged a*pico (γ). Opposite diel patterns were observed for the normalized a*pico (443) and a*pico (675) with maximum toward dawn or dusk and minimum toward midday at 4 stations under low-irradiance (LI) conditions and vice versa at 3 stations under high-irradiance (HI) conditions. The absorption efficiency factors at red absorption peak, Q
a (675), were determined by reconstruction with intracellular chlorophyll a concentration and cell diameter. The normalized Q
a (675) also showed diel pattern with maximum toward midday and minimum toward dawn or dusk under LI. The diel pattern in a*pico (675) and Q
a (675) were primarily caused by changes in intracellular chlorophyll a concentration due to photoadaptation under LI. The diel pattern in a*pico (443) was influenced by pigmentation, as recognized by blue to red ratio [a*pico (443)/a*pico (675)] under HI. This study proposed that the opposite diel pattern in a*pico (γ) might occur for a wide range of algal species. The results presented here have important consequences for the interpretation of diel variations in optical properties observed in the open ocean. 相似文献