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91.
R. Thomas J.D. Webster D. Rhede W. Seifert K. Rickers H.-J. Frster W. Heinrich P. Davidson 《Lithos》2006,91(1-4):137-149
Fractional crystallization of peraluminous F- and H2O-rich granite magmas progressively enriches the remaining melt with volatiles. We show that, at saturation, the melt may separate into two immiscible conjugate melt fractions, one of the fractions shows increasing peraluminosity and the other increasing peralkalinity. These melt fractions also fractionate the incompatible elements to significantly different degrees. Coexisting melt fractions have differing chemical and physical properties and, due to their high density and viscosity contrasts, they will tend to separate readily from each other. Once separated, each melt fraction evolves independently in response to changing T/P/X conditions and further immiscibility events may occur, each generating its own conjugate pair of melt fractions. The strongly peralkaline melt fractions in particular are very reactive and commonly react until equilibrium is attained. Consequently, the peralkaline melt fraction is commonly preserved only in the isolated melt and mineral inclusions.
We demonstrate that the differences between melt fractions that can be seen most clearly in differing melt inclusion compositions are also visible in the composition of the resulting ore-forming and accessory minerals, and are visible on scales from a few micrometers to hundreds of meters. 相似文献
92.
Thomas A. Vogel Timothy P. Flood Lina C. Patino Melissa S. Wilmot Raymond Patrick R. Maximo Carmencita B. Arpa Carlo A. Arcilla James A. Stimac 《Contributions to Mineralogy and Petrology》2006,151(3):267-281
Silicic volcanic deposits (>65 wt% SiO2), which occur as domes, lavas and pyroclastic deposits, are relatively abundant in the Macolod Corridor, SW Luzon, Philippines.
At Makiling stratovolcano, silicic domes occur along the margins of the volcano and are chemically similar to the silicic
lavas that comprise part of the volcano. Pyroclastic flows are associated with the Laguna de Bay Caldera and these are chemically
distinct from the domes and lavas at Makiling stratovolcano. As a whole, samples from the Laguna de Bay Caldera contain lower
concentrations of MgO and higher concentrations of Fe2O3(t) than the samples from domes and lavas. The Laguna de Bay samples are more enriched in incompatible trace elements. The silicic
rocks from the domes, Makiling Volcano and Laguna de Bay Caldera all contain high alkalis and high K2O/Na2O ratios. Melting experiments of primitive basalts and andesites demonstrate that it is difficult to produce high K2O/Na2O silicic magmas by fractional crystallization or partial melting of a low K2O/Na2O source. However, recent melting experiments (Sisson et al., Contrib Mineral Petrol 148:635–661, 2005) demonstrate that extreme
fractional crystallization or partial melting of K-rich basalts can produce these silicic magmas. Our model for the generation
of the silicic magmas in the Macolod Corridor requires partial melting of mantle-derived, evolved, moderate to K-rich, crystallized
calc-alkaline magmas that ponded and crystallized in the mid-crust. Major and trace element variations, along with oxygen
isotopes and ages of the deposits, are consistent with this model.
Electronic Supplementary Material Supplementary material is available for this article at 相似文献
93.
S. C. Choi Onyx W. H. Wai Thomas W. H. Choi X. D. Li C. W. Tsang 《Environmental Geology》2006,51(3):455-461
Partitioning of heavy metals (Cd, Cr, Cu, Pb, Zn) in marine sediments collected from various sites in Hong Kong waters were
determined using sequential extraction method. Sediments from Kellette Bank, located in Victoria Harbour, had higher metal
concentrations especially Cu and Zn than most other sites. Slightly over 20% of total Cu and Cr existed as readily available
forms in Peng Chau and Kellette Bank. At most sampling sites, over 15% of the Cu existed as the exchangeable form indicating
that Cu could be readily released into the aqueous phase from sediments. A significantly higher percentage of Pb and Zn was
associated with the three non-residual fractions. Hence, there is a greater environmental concern for remobilization of Pb
and Zn compared with Cr. The high amount of residual Cd (>50%) and the relatively lower Cd content indicate that little environmental
concern is warranted for the remobilization of Cd. Distribution of metals in sediments collected from different depth at Kellette
Bank shows that metal concentrations decreased with profile depth. The levels of Pb and Zn associated with the two readily
available fractions increased sharply in the surface sediment. These metals represented the pollutants, which were introduced
into the area in the mid-eighties through early nineties as a result of rapid economic and industrial development in the territory.
As significant portions of these metals were bound to the readily available phases in the surface sediments, metal remobilization
could be a concern.
An erratum to this article can be found at 相似文献
94.
Thomas O. Graff 《The Professional geographer》2006,58(1):54-64
The three largest discount chains, Kmart, Target, and Wal‐Mart, have adopted the supercenter format for expansion. This article examines the locations of and the competition among these supercenters. Wal‐Mart has the greatest number of supercenters and is driving the expansion of the supercenter format. Both Kmart and Target have clustered their supercenters in a small number of metropolitan markets. In contrast to Wal‐Mart and Kmart, Target has focused on a middle‐class rather than a blue‐collar clientele. Now Kmart is struggling following a declaration of bankruptcy. Wal‐Mart has largely defeated its supercenter competitors and now is confronting the major grocery chains for grocery sales. 相似文献
95.
96.
Márian Urban Rainer Thomas Vratislav Hurai Patrik Koneèný Martin Chovan 《Mineralium Deposita》2006,40(8):867-873
CO2 inclusions with density up to 1,197 kg m−3 occur in quartz–stibnite veins hosted in the low-grade Palaeozoic basement of the Gemericum tectonic unit in the Western Carpathians. Raman microanalysis corroborated CO2 as dominant gas species accompanied by small amounts of nitrogen (<7.3 mol%) and methane (<2.5 mol%). The superdense CO2 phase exsolved from an aqueous bulk fluid at temperatures of 183–237°C and pressures between 1.6 and 3.5 kbar, possibly up to 4.5 kbar. Low thermal gradients (∼12–13°C km−1) and the CO2–CH4–N2 fluid composition rule out a genetic link with the subjacent Permian granites and indicate an external, either metamorphogenic (oxidation of siderite, dedolomitization) or lower crustal/mantle, source of the ore-forming fluids.According to microprobe U–Pb–Th dating of monazite, the stibnite-bearing veins formed during early Cretaceous thrusting of the Gemeric basement over the adjacent Veporic unit. The 15- to 18-km depth of burial estimated from the fluid inclusion trapping PT parameters indicates a 8- to 11-km-thick Upper Palaeozoic–Jurassic accretionary complex overlying the Gemeric basement and its Permo-Triassic autochthonous cover. 相似文献
97.
The FORMOSAT-3/COSMIC mission is a microsatellite mission for weather forecast, climate monitoring, and atmospheric, ionospheric and geodesy research. This mission is a collaborative Taiwan-USA science experiment to deploy a constellation of six microsatellites in low Earth orbits. The mission life is 2 years with a goal of 5 years. The final mission orbit has an altitude of 750–800 km. Each satellite consists of three science payloads: global positioning system (GPS) occultation experiment (GOX) payload, tiny ionospheric photometer (TIP) and tri-band beacon (TBB). The GOX will collect the GPS signals for the study on atmosphere, ionosphere, and geodesy. The TIP and TBB can provide the electron distribution information for ionospheric research. The deployment of the FORMOSAT-3 constellation and the resulting influence on the occultation sounding distributions are reported. Details are also given on GOX, TIP, and TBB payload operations and the contributions of the Taiwan Science Team. 相似文献
98.
Modelling Korean extreme rainfall using a Kappa distribution and maximum likelihood estimate 总被引:6,自引:0,他引:6
Summary Attempts to use the 4-parameter Kappa distribution (K4D) with the maximum likelihood estimates (MLE) on the summer extreme
daily rainfall data at 61 gauging stations over South Korea have been made to obtain reliable quantile estimates for several
return periods. A numerical algorithm for searching MLE of K4D by minimizing the negative log-likelihood function with penalty
method has been described. The isopluvial maps of estimated design values corresponding to selected return periods have been
presented. The highest return values are centered at sites in the south-western part of the Korean peninsula. The distribution
of return values for annual maxima of 2-day precipitation (AMP2) is more similar to the climatological features of annual
total precipitation of Korea than that of annual maxima of daily precipitation (AMP1). Our results of return values delineate
well the horizontal patterns of the heavy precipitation over the Korean peninsula.
Received January 15, 2001 Revised October 8, 2001 相似文献
99.
Implications of the relationship between catchment vegetation type and the variability of annual runoff 总被引:1,自引:0,他引:1
The impact of changing catchment vegetation type on mean annual runoff has been known for some time, however, the impact on the variability of annual runoff has been established only recently. Differences in annual actual evapotranspiration between vegetation types and the potential effect of changing vegetation type on mean annual runoff and the variability of annual runoff are briefly reviewed. The magnitude of any change in the variability of annual runoff owing to a change in catchment vegetation type is related to the pre‐ and post‐change vegetation types and the seasonality of precipitation, assuming that the variability of annual precipitation remains constant throughout. Significant implications of the relationship between vegetation type and the variability of annual runoff are presented and discussed for water resource management, stream ecology and fluvial geomorphology. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
100.
The Upper Cretaceous Juniper Ridge Conglomerate (JRC) near Coalinga, California, provides a rare, high-quality exposure of a submarine channel to overbank transition. The facies architecture of the JRC comprises a thick, predominantly mudstone sequence overlain by a channellized conglomerate package. Conglomeratic bounding surfaces truncate successions of interbedded turbiditic sandstones and mudstones both vertically and laterally. Thick-bedded, massive sandstones are interbedded with conglomerates. Facies architecture, palaeocurrent indicators, slump features, sandstone percentages and sandstone bed thickness trends lead to the interpretation that these elements comprise channel and overbank facies. A vertical sequence with conglomerate at the base, followed by thick-bedded sandstone, and capped by interbedded turbiditic sandstone and mudstone form a fining-upward lithofacies association that is interpreted as a single channel-fill/overbank system. Three similar lithofacies associations can be related to autocyclic processes of thalweg migration and submarine fan aggradation or to allocyclically driven changes in sediment calibre. 相似文献