Crystal retention,fractionation and crustal assimilation in a convecting magma chamber,Nisyros Volcano,Greece   总被引：2，自引：0，他引：2  

L. Francalanci  J. C. Varekamp  G. Vougioukalakis  M. J. Delant  F. Innocenti  P. Manetti 《Bulletin of Volcanology》1995,56(8):601-620

Nisyros island is a calc-alkaline volcano, built up during the last 100 ka. The first cycle of its subaerial history includes the cone-building activity with three phases, each characterized by a similar sequence: (1) effusive and explosive activity fed by basaltic andesitic and andesitic magmas; and (2) effusive andextrusive activity fed by dacitic and rhyolitic magmas. The second eruptive cycle includes the caldera-forming explosive activity with two phases, each consisting of the sequence: (1) rhyolitic phreatomagmatic eruptions triggering a central caldera collapse; and (2) extrusion of dacitic-rhyolitic domes and lava flows. The rocks of this cycle are characteized by the presence of mafic enclaves with different petrographic and chemical features which testify to mixing-mingling processes between variously evolved magmas. Jumps in the degree of evolution are present in the stratigraphic series, accompanied by changes in the porphyritic index. This index ranges from 60% to about 5% and correlates with several teochemical parameters, including a negative correlation with Sr isotope ratios (0.703384–0.705120). The latter increase from basaltic andesites to intermediate rocks, but then slightly decrease in the most evolved volcanic rocks. The petrographic, geochemical and isotopic characteristics can be largely explained by processes occurring in a convecting, crystallizing and assimilating magma chamber, where crystal sorting, retention, resorption and accumulation take place. A group of crystal-rich basaltic andesites with high Sr and compatible element contents and low incompatible elements and Sr isotope ratios probably resulted from the accumulation of plagioclase and pyroxene in an andesitic liquid. Re-entrainment of plagioclase crystals in the crystallizing magma may have been responsible for the lower ⁸⁷Sr/⁸⁶Sr in the most evolved rocks. The gaps in the degree of evolution with time are interpreted as due to liquid segregation from a crystal mush once critical crystallinity was reached. At that stage convection halted, and a less dense, less porphyritic, more evolved magma separated from a denser crystal-rich magma portion. The differences in incompatible element enrichment of pre-and post-caldera dacites and the chemical variation in the post-caldera dome sequence are the result of hybridization of post-caldera dome magmas with more mafic magmas, as represented by the enclave compositions. The occurrence of the quenched, more mafic magmas in the two post-caldera units suggests that renewed intrusion of mafic magma took place after each collapse event.  相似文献   

The effects of anthropogenic nutrient enrichment on turtle grass (Thalassia testudinum) in Sarasota Bay,Florida     

Tomasko  David A.  Dawes  Clinton J.  Hall  Margaret O. 《Estuaries and Coasts》1996,19(2):448-456

Four meadows of turtle grass (Thalassia testudinum Banks ex Konig) in Sarasota Bay, Florida were sampled on a bimonthly basis from June 1992 to July 1993 to determine spatial and temporal variation in short shoot density, biomass, productivity, and epiphyte loads. Concurrent with the seagrass sampling, quarterly water-quality monitoring was undertaken at ≥3 sites in the vicinity of each studied seagrass meadow. Three months after termination of the seagrass sampling effort, a biweekly water-quality monitoring program was instituted at two of the seagrass sampling sites. In addition, a nitrogen loading model was calibrated for the various watersheds influencing the seagrass meadows. Substantial spatial and temporal differences in turtle grass parameters but smaller spatial variation in water quality parameters are indicated by data from both the concurrent quarterly monitoring program and the biweekly monitoring program instituted after termination of the seagrass study. Turtle grass biomass and productivity were negatively correlated with watershed nitrogen loads, while water quality parameters did not clearly reflect differences in watershed nutrient inputs. We suggest that traditional water-quality monitoring programs can fail to detect the onset or continuance of nutrient-induced declines in seagrass health. Consequently, seagrass meadows should be monitored directly as a part of any effort to determine status and/or trends in the health of estuarine environments. *** DIRECT SUPPORT *** A01BY074 00029

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Predictive Depositional Model for Glacial Aquifers     

Mark T. Stewart 《Ground water》1981,19(2):133-137

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REPLY TO the preceding Discussion by Göksel Türk of "Interpretation of Hydrochemical Facies by Factor Analysis"     

Sam B. Upchurch 《Ground water》1979,17(2):213-215

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Multivariate analysis of sedimentary environments using grain-size frequency distributions     

Richard L. Chambers  Sam B. Upchurch 《Mathematical Geosciences》1979,11(1):27-43

Multivariate statistics were used to characterize and test the effectiveness of grain-size frequencies as environmental discriminators. Sediment from the following two depositional systems along eastern Lake Michigan were studied: (1) a closed system with respect to available grain sizes (Little Sable Point), and (2) an open system (Sleeping Bear Point-Manitou Passage). Principal components analysis shows that grain-size distributions are composed of two or more subgroups that reflect surface creep bedload, mixed suspension bedload, and uniform suspension. Discriminant function and principal latent vector analyses of the Little Sable Point environments show that, when available sediment is limited with respect to grain size (0.5 φto 3.0 φ), similar size distributions can occur in environments supposedly characterized by different energy conditions. Sediment in the Sleeping Bear Point-Manitou Passage system is not restricted to available grain sizes and the environments discriminated very well (α < 0.001). The grain-size distributions are such that they reflect differences in energy conditions within the environments. It is apparent that the grain sizes available to a depositional system control to a great extent the effectiveness of environmental discrimination.  相似文献   

Effects of Sea Water Canals on Fresh Water Resources: An Example from Big Pine Key, Florida   总被引：1，自引：0，他引：1  

C.D. Langevin  M.T. Stewart  C.M. Beaudoin 《Ground water》1998,36(3):503-513

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Soft-sediment deformation (fluid escape) features in a coarse-grained pyroclastic-surge deposit, north-central New Mexico     

Bruce W. Nocita 《Sedimentology》1988,35(2):275-285

ABSTRACT
The Puye Formation in north-central New Mexico is a very coarse-grained fanglomerate which was deposited on the eastern flank of the Jemez caldera. Pyroclastic deposits occur within the Puye in the form of airfall pumice beds and the remnant of at least one pyroclastic-surge deposit. This pyroclastic-surge deposit shows the effects of fluidization and soft-sediment deformation in the form of: (1) intrusive sedimentary plumes; (2) upwardly injected gravelly pipes; (3) 'pocket structures' similar to those of Postma (1983), and; (4) oversteepened and deformed cross-stratification.
Fluidization and soft-sediment deformation resulted from a combination of the mechanical instability and high, possibly pressurized, fluid content of the deposit. This metastable condition was a consequence of the nature of the flow which deposited the sediment: a rapidly depositing, high-velocity sediment gravity flow. The fluids in pyroclastic surges may be either gas or liquid. However, because of the coarse grain-size of the fluidized sediment, it is suggested that liquids were responsible for the features described in this paper. Evidence also suggests that locally fluidization, liquefaction, and soft-sediment deformation took place penecontemporaneously with deposition.  相似文献   

Evaluation of Transient Electromagnetic Soundings for Deep Detection of Conductive Fluids   总被引：1，自引：0，他引：1  

Mark Stewart  Michael C. Gay 《Ground water》1986,24(3):351-356

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Biogeochemical Gradients: Microbes, Measurements, and Modeling     

Danielle Fortin  Thomas Pichler  Chad Saltikov 《Applied Geochemistry》2007,22(12):2567

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Extremes of Daily Rainfall in West Central Florida   总被引：1，自引：0，他引：1  

Saralees Nadarajah 《Climatic change》2005,69(2-3):325-342

Annual maxima of daily rainfall data dating from 1901 to 2003 are modeled for fourteen locations in West Central Florida. The generalized extreme value (GEV) distribution is fitted to data from each location. The location parameter of the GEV is formulated as a function of time to adequately describe the extremes of rainfall and to predict their future behavior. We find evidence of non-stationarity in the form of trends for eight of the fourteen locations considered. We quantify the change in extreme rainfall for each location and provide return levels for the years 2010, 2020, 2050 and 2100. We also derive estimates of return levels for daily rainfall and provide a classification of the fourteen locations based on the degree of severity of these estimates. This paper provides the first application of extreme value distributions to rainfall data specifically from Florida.  相似文献