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91.
J. M. Watkins J. D. Clemens P. J. Treloar 《Contributions to Mineralogy and Petrology》2007,154(1):91-110
Two natural, low K2O/Na2O, TTG tonalitic gneisses (one hornblende-bearing and the other biotite-bearing) were partially melted at 0.8–1.2 GPa (fluid-absent).
The chief melting reactions involve the breakdown of the biotite and hornblende. The hornblende tonalite is slightly less
fertile than the biotite tonalite, but melt volumes reach around 30% at 1,000°C. This contrasts with results of most previous
work on more potassic TTGs, which generally showed much lower fertility, though commonly producing more potassic melts. Garnet
is formed in biotite-bearing tonalitic protoliths at P > 0.8 GPa and at > 1.0 GPa in hornblende-bearing tonalitic protoliths. All fluid-absent experiments produced peraluminous
granitic to granodioritic melts, typically with SiO2 > 70 wt.%. For the biotite tonalite, increasing T formed progressively more melt with progressively lower K2O/Na2O. However, the compositions of melts from the hornblende tonalite do not vary significantly with T. With increasing P, melts from the biotite tonalite become less potassic, due to the increasing thermal stability of biotite. For the hornblende
tonalite, again there is no consistent trend. Fluid-absent melting of sodic TTGs produces melts with insufficient K2O to model the magmas that formed the voluminous, late, potassic granites that are common in Archaean terranes. Reconnaissance
fluid-present experiments at 0.6 GPa imply that H2O-saturated partial melting of TTGs is also not a viable process for producing magmas that formed these granites. The protoliths
for these must have been more potassic and less silicic. Nevertheless, at granulite-facies conditions, sodic TTGs will produce
significant quantities of broadly leucogranodioritic melt that will be more potassic than the protoliths. Upward abstraction
of this melt would result in some LILE depletion of the terrane. Younger K-rich magmatism is unlikely to represent recycling
of TTG crust on its own, and it seems most likely that evolved crustal rocks and/or highly enriched mantle must be involved.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
92.
93.
The island of St. Paul in the Indian Ocean is located on the axis of the southeastern branch of the Indian Ocean Rise, as is the similar volcano of Amsterdam, 80 km to the north. Both volcanoes and possibly part of the local ridge are formed of a high-alumina plagioclase tholeiite making this a distinctive volcanic province. Lavas with Al2O2 contents of 12 to 22% are directly related by plagioclase fractionation. Residual rocks are a distinctive low silica, low alumina, potassic andesite with andesine and even olligoclase feldspar. Parallel lines of evolution exist in the sea floor plagioclase tholeiites, which differ only in slightly lower tenor of Sr and potassium group elements, and in the Steens Mountain tholeiites of Oregon, which differ in their significantly higher Sr and K group elements 相似文献
94.
95.
Experimental batch and miscible-flow cultures were studied in order to determine the mechanistic pathways of microbial Fe(III)
respiration in ferruginous smectite clay, NAu-1. The primary purpose was to resolve if alteration of smectite and release
of Fe precedes microbial respiration. Alteration of NAu-1, represented by the morphological and mineralogical changes, occurred
regardless of the extent of microbial Fe(III) reduction in all of our experimental systems, including those that contained
heat-killed bacteria and those in which O2, rather than Fe(III), was the primary terminal electron acceptor. The solid alteration products observed under transmission
electron microscopy included poorly crystalline smectite with diffuse electron diffraction signals, discrete grains of Fe-free
amorphous aluminosilicate with increased Al/Si ratio, Fe-rich grains, and amorphous Si globules in the immediate vicinity
of bacterial cells and extracellular polymeric substances. In reducing systems, Fe was also found as siderite. The small amount
of Fe partitioned to the aqueous phase was primarily in the form of dissolved Fe(III) species even in the systems in which
Fe(III) was the primary terminal electron acceptor for microbial respiration. From these observations, we conclude that microbial
respiration of Fe(III) in our laboratory systems proceeded through the following: (1) alteration of NAu-1 and concurrent release
of Fe(III) from the octahedral sheets of NAu-1; and (2) subsequent microbial respiration of Fe(III). 相似文献
96.
97.
98.
Natural Hazards - The objective of this research is to establish a model that characterizes integrated humanitarian operations management in response to flood disasters, during which an optimal... 相似文献
99.
Geraint A. Tarling Thor Klevjer Sophie Fielding Jon Watkins Angus Atkinson Eugene Murphy Rebecca Korb Mick Whitehouse Russell Leaper 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(11):1994-2012
Swarming is a fundamental part of the life of Euphausia superba, yet we still know very little about what drives the considerable variability in swarm shape, size and biomass. We examined swarms across the Scotia Sea in January and February 2003 using a Simrad EK60 (38 and 120 kHz) echosounder, concurrent with net sampling. The acoustic data were analysed through applying a swarm-identification algorithm and then filtering out all non-krill targets. The area, length, height, depth, packing-concentration and inter-swarm distance of 4525 swarms was derived by this method. Hierarchical clustering revealed 2 principal swarm types, which differed in both their dimensions and packing-concentrations. Type 1 swarms were generally small (<50 m long) and were not very tightly packed (<10 ind. m−3), whereas type 2 swarms were an order of magnitude larger and had packing concentrations up to 10 times greater. Further sub-divisions of these types identified small and standard swarms within the type 1 group and large and superswarms within the type 2 group. A minor group (swarm type 3) was also found, containing swarms that were isolated (>100 km away from the next swarm). The distribution of swarm types over the survey grid was examined with respect to a number of potential explanatory variables describing both the environment and the internal-state of krill (namely maturity, body length, body condition). Most variables were spatially averaged over scales of 100 km and so mainly had a mesoscale perspective. The exception was the level of light (photosynthetically active radiation (PAR)) for which measurements were specific to each swarm. A binary logistic model was constructed from four variables found to have significant explanatory power (P<0.05): surface fluorescence, PAR, krill maturity and krill body length. Larger (type 2) swarms were more commonly found during nighttime or when it was overcast during the day, when surface fluorescence was low, and when the krill were small and immature. A strong pattern of diel vertical migration was not observed although the larger and denser swarms tended to occur more often at night than during the day. The vast majority of krill were contained within a minor fraction of the total number of swarms. These krill-rich swarms were more common in areas dominated by small and immature krill. We propose that, at the mesoscale level, the structure of swarms switches from being predominantly large and tightly packed to smaller and more diffuse as krill grow and mature. This pattern is further modulated according to feeding conditions and then level of light. 相似文献