Basic lavas of the Archean La Grande Greenstone belt: Products of polybaric fractionation and crustal contamination     

Thomas Skulski  Andrew Hynes  Don Francis 《Contributions to Mineralogy and Petrology》1988,100(2):236-245

Despite the fact that some greenstone belts preserve the record of contemporaneous komatiitic and tholeiitic volcanism, a genetic link between the two is not widely accepted. The significance of a compositional gap seperating these magma types and differences in their respective degree of light rare earth element (LREE) enrichment, cited as evidence against a derivative relationship, are complicated by the possibility of crustal assimilation by magmas of komatiitic affinity. In the Archean La Grande Greenstone belt of northern Quebec a succession of metamorphosed tholeiitic basalts and younger, high-Mg, LREE-enriched andesites are preserved. The tholeiites are differentiated basaltic rocks whose chemical compositions appear to have been controlled by low pressure, gabbroic fractional crystallization and are similar to Type 1 MORB. Parental magmas were probably high-Mg liquids of compositions similar to komatiitic basalts which also occur in the greenstone belt. These high-Mg liquids are believed to be themselves the product of high pressure, OLIV+OPX fractional crystallization of more magnesian primary liquids of komatiitic composition. The higher La/Sm ratios of komatiitic basalts and tholeiites relative to komatiites in this belt, can be explained by small degrees of crustal assimilation. In the central part of the belt, late-stage, mafic igneous rocks have chemical compositions similar to Archean examples of contaminated volcanic rocks (e.g., Kambalda, Australia). These late-stage lavas consist of basalts and andesites with high-Mg, Ni and Cr abundances, LREE-enriched profiles and low Ti abundances. They are believed to be the products of crustal assimilation and crystallization of OPX-PLAG-CPX from high-Mg liquids of komatiitic affinity. The volcanic stratigraphy records the progressive effects of crustal contamination through time. A light sialic crust may have initially acted as a density barrier, preventing the eruption of primary high-Mg liquids and forcing fractionation at depth which produced more buoyant compositions. With subsequent thinning of the crust, the density barrier presumably failed, and primary liquids migrated directly toward the surface. Reaction of these liquids with tonalitic crust produced contaminated differentiates.  相似文献   

Laboratory study of wave and turbulence characteristics in narrow-band irregular breaking waves     

Francis C. K. Ting   《Coastal Engineering》2002,46(4)

Wave elevations and water particle velocities were measured in a laboratory surf zone created by the breaking of a narrow-band irregular wave train on a 1/35 plane slope. The incident waves form wave groups that are strongly modulated. It is found that the waves that break close to the shoreline generally have larger wave-height-to-water-depth ratios before breaking than the waves that break farther offshore. After breaking, the wave-height-to-water-depth ratio for the individual waves approaches a constant value in the inner surf zone, while the standard deviation of the wave period increases as the still water depth decreases. In the outer surf zone, the distribution of the period-averaged turbulent kinetic energy is closely correlated to the initial wave heights, and has a wider variation for narrow-band waves than for broad-band waves. In the inner surf zone, the distribution of the period-averaged turbulent kinetic energy is similar for narrow-band waves and broad-band waves. It is found that the wave elevation and turbulent kinetic energy time histories for the individual waves in a wave group are qualitatively similar to those found in a spilling regular wave. The time-averaged transport of turbulent kinetic energy by the ensemble-averaged velocity and turbulence velocity under the irregular breaking waves are also consistent with the measurements obtained in regular breaking waves. The experimental results indicate that the shape of the incident wave spectrum has a significant effect on the temporal and spatial variability of wave breaking and the distribution of turbulent kinetic energy in the outer surf zone. In the inner surf zone, however, the distribution of turbulent kinetic energy is relatively insensitive to the shape of the incident wave spectrum, and the important parameters are the significant wave height and period of the incident waves, and the beach slope.  相似文献   

A numerical study on the mixed layer depth variability and its influence on the sea surface temperature during 2013–2014 in the Bay of Bengal and Equatorial Indian Ocean     

Sen  Radharani  Francis  Pavanathara Augustine  Chakraborty  Arun  Effy  John B. 《Ocean Dynamics》2021,71(5):527-543

Ocean Dynamics - This study addresses the air–sea interaction processes and mixed layer variability, which cause the intraseasonal oscillations in the sea surface temperature (SST) during...  相似文献   

The social construction of geographical information systems     

Francis Harvey 《International journal of geographical information science》2013,27(8):711-713

  相似文献   

Code/space: software and everyday life,by Rob Kitchen and Martin Dodge     

Francis Harvey 《International journal of geographical information science》2013,27(10):1999-2001

  相似文献   

High energy neutrinos from the TeV Blazar 1ES 1959 + 650     

Francis Halzen  Dan Hooper   《Astroparticle Physics》2005,23(6):537-542

The AMANDA neutrino telescope has recently reported the detection of high-energy neutrinos spatially and temporally coincident with the flaring of the TeV blazar 1ES 1959 + 650. If high-energy neutrinos are in fact generated by this blazar, it would be the first strong evidence for the hadronic acceleration of cosmic rays. At present, the statistical significance of this observation cannot be reliably assessed, however. In this letter, we investigate whether circumstances exist where the source can produce the flux implied by the coincident events. We show that if the TeV gamma-ray emission observed from 1ES 1959 + 650 or other nearby TeV blazars is the result of accelerated protons interacting with nucleons, it is reasonable that AMANDA could detect several events during a flaring period. Such rates require that the spectral index of the source be rather high (for instance 2.8 for 1ES 1959 + 650) and that the Lorentz factor of the jet be fairly small (Γ  1).  相似文献   

LS I +61 303 as a potential neutrino source on the light of magic results     

Diego F. Torres  Francis Halzen 《Astroparticle Physics》2007,27(6):500-508

Very high energy γ-rays have recently been detected from the microquasar LS I +61 303 using the MAGIC telescope. A phenomenological study on the concomitant neutrinos that would be radiated if the γ-ray emission is hadronic in origin is herein presented. Neutrino oscillations are considered, and the expected number of events in a km-scale detector such as ICECUBE is computed under different assumptions including orbital periodicity and modulation, as well as different precision in the modeling of the detector. We argue that the upper limits already imposed on the neutrino emission of LS I +61 303 using AMANDA-II and the forthcoming measurements by ICECUBE may significantly constrain – in an independent and unbiased way – the γ-ray to neutrino flux ratio, and thus the possibility of a hadronic origin of the γ-rays. The viability of hadronic models based on wind–jet interactions in the LS +61 303 system after MAGIC measurements is discussed.  相似文献   

Cosmic neutrinos from the sources of galactic and extragalactic cosmic rays     

Francis Halzen 《Astrophysics and Space Science》2007,309(1-4):407-414

Although kilometer-scale neutrino detectors such as IceCube are discovery instruments, their conceptual design is very much anchored to the observational fact that Nature produces protons and photons with energies in excess of 10²⁰ eV and 10¹³ eV, respectively. The puzzle of where and how Nature accelerates the highest energy cosmic particles is unresolved almost a century after their discovery. From energetics considerations we anticipate on the order of 10–100 neutrino events per kilometer squared per year pointing back at the source(s) of both galactic and extragalactic cosmic rays. In this context, we discuss the results of the AMANDA and IceCube neutrino telescopes which will deliver a kilometer-square-year of data over the next 3 years.  相似文献   

Towards improved ground models for slope instability evaluations through better characterization of sediment-hosted gas-hydrates     

D. A. Gunn  L. M. Nelder  C. A. Rochelle  K. Bateman  P. D. Jackson  M. A. Lovell  P. R. N. Hobbs  D. Long  J. G. Rees  P. Schultheiss  J. Roberts  T. Francis 《地学学报》2002,14(6):443-451

ABSTRACT Recently developed effective stress-controlled geophysical property models are used in passive-margin slope instability analyses including simulated earthquake motion. The pressure–temperature (P–T) history of sediment-hosted gas hydrate may significantly alter the geophysical property profile of the sediment column (e.g. metastable cement or increased pore pressures). This can result in significant amplification of earthquake ground motion, and thus seabed instability, where hydrates are present. Published studies suggest destabilization of these high-pressure/low-temperature sediment-hosted hydrates could trigger catastrophic slope failures with consequent liberation of 'greenhouse' gases and significant effects on global climate. To provide improved ground models for slope instability analyses we are investigating the influence of P–T history on hydrate distribution in sediments through the development of laboratory techniques to enable geophysical quantification of hydrate morphology and fabric on hydrate stability.  相似文献   

4. Building of a Habitable Planet     

Hervé Martin  Francis Albarède  Philippe Claeys  Muriel Gargaud  Bernard Marty  Alessandro Morbidelli  Daniele L. Pinti 《Earth, Moon, and Planets》2006,98(1-4):97-151

Except the old Jack Hills zircon crystals, it does not exit direct record of the first 500 Ma of the Earth history. Consequently, the succession of events that took place during this period is only indirectly known through geochemistry, comparison with other telluric planets, and numerical modelling. Just after planetary accretion several episodes were necessary in order to make life apparition and development possible and to make the Earth surface habitable. Among these stages are: the core differentiation, the formation of a magma ocean, the apparition of the first atmosphere, oceans and continents as well as the development of magnetic field and of plate tectonics. In the same time, Earth has been subject to extraterrestrial events such as the Late Heavy Bombardment (LHB) between 3.95 and 3.8 Ga. Since 4.4–4.3 Ga, the conditions for pre-biotic chemistry and appearance of life were already met (liquid water, continental crust, no strong meteoritic bombardment, etc...). This does not mean that life existed as early, but this demonstrates that all necessary conditions assumed for life development were already present on Earth.  相似文献