Significance of strain localization and fracturing in relation to hydrothermal mineralization at Mount Isa, Australia   总被引：1，自引：0，他引：1  

Klaus Gessner  Peter A. Jones  Andy R. Wilde  Michael Kühn   《Journal of Geochemical Exploration》2006,89(1-3):129

The rheology of layered meta-sedimentary rocks, and their orientation and position relative to major fault systems were the key controls on Proterozoic hydrothermal copper mineralization at Mount Isa, Australia. Compositional layering in the host rock partitioned mechanical behavior and strain, leading to selective permeability generation and the focusing of fluid flow. Shale layers preferentially failed by plastic shearing, whereas meta-siltstones remained elastic or failed in tension depending on magnitude of deformation and fluid pressure. Numerical simulations support the hypothesis that the orientation of layering and the proximity to major fault systems controlled fracturing and permeability increase in the Urquhart shale. The dilating shale provided a pathway for an upward-flowing, reduced basement fluid, from which quartz was precipitated during cooling. During a later event, the reactivation of steep structures provided access to surface derived oxidized metal-bearing brine, causing the precipitation of dolomite followed by chalcopyrite ore in the brecciated silicified shale.  相似文献   

Bringing it all back home: The extensification and ‘overflowing’ of work: The case of San Francisco’s new media households     

Helen Jarvis  Andy C. Pratt 《Geoforum》2006,37(3):331-339

This paper explores the extensification of work—that is the distribution or exporting of work across different spaces/scales and times—and its impact on individual workers and households. We argue that contracting out and the work life balance debates might be developed more usefully within the holistic framework of extensification. The key process that we follow can be described as overflowing. We contrast the universally positive representations of spillovers and embedding that we are familiar with in economic geographies with the more negatively characterised overflowing of work into and out of the household. The paper is built around a case study of those involved in the new media industry in San Francisco: households, workers and companies.  相似文献   

Crystallization of Cr-poor and Cr-rich megacryst suites from the host kimberlite magma: implications for mantle structure and the generation of kimberlite magmas     

Andy?MooreEmail author  Elena?Belousova 《Contributions to Mineralogy and Petrology》2005,149(4):462-481

Cr-poor and Cr-rich megacryst suites, both comprising of varying proportions of megacrysts of orthopyroxene, clinopyroxene, garnet, olivine, ilmenite and a number of subordinate phases, coexist in many kimberlites, with wide geographic distribution. In rare instances, the two suites occur together on the scale of individual megacryst hand specimens. Deformation textures are common to both suites, suggesting an origin related to the formation of the sheared peridotites that also occur in kimberlites. Textures and compositions of the latter are interpreted to reflect deformation and metasomatism within the thermal aureole surrounding the kimberlite magma in the mantle. The megacrysts crystallized in this thermal aureole in pegmatitic veins representing small volumes of liquids derived from the host kimberlite magma, which were injected into a surrounding fracture network prior to kimberlite eruption. Close similarities between compositions of Cr-rich megacryst phases and those in granular lherzolites are consistent with early crystallization from a primitive kimberlite liquid. The low-Cr megacryst suite subsequently crystallized from residual Cr-depleted liquids. However, the Cr-poor suite also reflects the imprint of contamination by liquids formed by melting of inhomogeneously distributed mantle phases with low melting temperatures, such as calcite and phlogopite, present within the thermal aureole surrounding the kimberlite magma reservoir. Such carbonate-rich melts migrated into, and mixed with some, but not all, of the kimberlite liquids injected into the mantle fracture network. Contamination by the carbonate-rich melts changed the Ca–Mg and Mg–Fe crystal–liquid distribution coefficient, resulting in the crystallization of relatively Fe-rich and Ca-poor phases. The implied higher crystal-melt Mg–Fe distribution coefficient for carbonate-rich magmas accounts for the generation of small volumes of Mg-rich liquids that are highly enriched in incompatible elements (i.e. primary kimberlite magmas). The inferred metasomatic origin for the sheared peridotites implies that this suite provides little or no information regarding vertical changes in the thermal, chemical and mechanical characteristics of the mantle.  相似文献   

The BIMA Survey of Nearby Galaxies (BIMA SONG)     

Tamara T. Helfer  Michael W. Regan  Michele D. Thornley  Tony Wong  Kartik Sheth  Stuart N. Vogel  Douglas C.-J. Bock  LEO Blitz  Andy Harris 《Astrophysics and Space Science》2001,276(2-4):1131-1139

BIMA SONG is a systematic imaging study of the 3 mm CO J = 1 → 0molecular emission within the centres and discs of 44 nearby spiral galaxies on size scales of a few hundred parsecs (6-9"). The overall goal of the survey is to study the role of molecular gas in the evolution of spiral galaxies. To this end, BIMA SONG addresses 1) the distribution and physical conditions of the molecular gas in galactic discs and its relation to star formation, 2) the effects of a stellar bar on the kinematics of molecular gas, including the possible inflow of gas along a bar, and 3) the distribution and role of molecular gas in the central few hundred parsecs of active and quiescent galaxies. The source list includes all (except M33and M31) 44 galaxies of Hubble types Sa–Sd, with declinations δ >−20^°, visual magnitudes B < 11.0, velocities v _hel <2000 km s^-1, and inclinations i < 70^°. Beyond the specific scientific questions we will address, this survey will provide a unique database for astronomers who study galaxies at all wavelengths. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

New media, the new economy and new spaces   总被引：8，自引：0，他引：8  

Andy C. Pratt 《Geoforum》2000,31(4)

This paper counters proponents of the ‘weightless economy’ who have suggested the ‘death of distance’ in relation to economic and social activities that use the worldwide web (WWW). An analysis of new media developers in New York’s ‘Silicon Alley’ demonstrates that place and distance are still important. The most important aspect of this co-location is the possibility of social interaction. This paper points to the value of analysis of the material practice of the social (and the economic and cultural). The notion of ‘untraded dependencies’ is developed through looking at its manifestation and constitution in the specificity of space, time and economic activity.  相似文献   

Climate change implications in the northern coastal temperate rainforest of North America     

Colin S. Shanley  Sanjay Pyare  Michael I. Goldstein  Paul B. Alaback  David M. Albert  Colin M. Beier  Todd J. Brinkman  Rick T. Edwards  Eran Hood  Andy MacKinnon  Megan V. McPhee  Trista M. Patterson  Lowell H. Suring  David A. Tallmon  Mark S. Wipfli 《Climatic change》2015,130(2):155-170

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Radiocarbon and Luminescence Age Determinations on Mounds at Crystal River and Roberts Island,Florida, USA     

T.J. Pluckhahn  A.D. Hodson  W.J. Rink  V.D. Thompson  R.R. Hendricks  G. Doran  G. Farr  A. Cherkinsky  S.P. Norman 《Geoarchaeology》2015,30(3):238-260

Optically stimulated luminescence (OSL) has been employed successfully to determine the ages of palaeosols from earthen mounds in the southeastern USA, providing archaeologists with a means of dating monument construction in the absence of carbonaceous materials and geologists with a setting for understanding factors that can affect the luminescence intensity (i.e., burial dose) of soils. However, OSL dating has not been adequately tested on mounds whose principal component is sand, shell, or a combination of these two, despite the fact that monuments composed of such materials are common to the coasts and interior coastal plains of the region. Radiocarbon dating of bone collagen and soil‐carbon and OSL dating of quartz grains extracted from the fill of mounds at the Crystal River and Roberts Island sites on the west‐central coast of Florida, USA are used to determine the timing and history of mound construction at the sites. Comparison of OSL and radiocarbon ages on materials from the same or closely related contexts provides insight into factors influencing age determinations in mound fill deposits, particularly the type of construction material (sand or shell) and the manner in which these were deposited. The results contribute to the understanding of the temporal context of platform mound construction in southeastern USA.  相似文献   

On the generation of climate model ensembles     

Ned Haughton  Gab Abramowitz  Andy Pitman  Steven J. Phipps 《Climate Dynamics》2014,43(7-8):2297-2308

Climate model ensembles are used to estimate uncertainty in future projections, typically by interpreting the ensemble distribution for a particular variable probabilistically. There are, however, different ways to produce climate model ensembles that yield different results, and therefore different probabilities for a future change in a variable. Perhaps equally importantly, there are different approaches to interpreting the ensemble distribution that lead to different conclusions. Here we use a reduced-resolution climate system model to compare three common ways to generate ensembles: initial conditions perturbation, physical parameter perturbation, and structural changes. Despite these three approaches conceptually representing very different categories of uncertainty within a modelling system, when comparing simulations to observations of surface air temperature they can be very difficult to separate. Using the twentieth century CMIP5 ensemble for comparison, we show that initial conditions ensembles, in theory representing internal variability, significantly underestimate observed variance. Structural ensembles, perhaps less surprisingly, exhibit over-dispersion in simulated variance. We argue that future climate model ensembles may need to include parameter or structural perturbation members in addition to perturbed initial conditions members to ensure that they sample uncertainty due to internal variability more completely. We note that where ensembles are over- or under-dispersive, such as for the CMIP5 ensemble, estimates of uncertainty need to be treated with care.  相似文献   

Assessing scalar concentration footprint climatology and land surface impacts on tall-tower CO2 concentration measurements in the boreal forest of central Saskatchewan,Canada     

Baozhang Chen  Huifang Zhang  Nicholas C. Coops  Dongjie Fu  Douglas E. J. Worthy  Guang Xu  T. Andy Black 《Theoretical and Applied Climatology》2014,118(1-2):115-132

Reducing the large uncertainties in current estimates of CO₂ sources and sinks at regional scales (10²–10⁵ km²) is fundamental to improving our understanding of the terrestrial carbon cycle. Continuous high-precision CO₂ concentration measurements on a tower within the planetary boundary layer contain information on regional carbon fluxes; however, its spatial representativeness is generally unknown. In this study, we developed a footprint model (Simple Analytical Footprint model based on Eulerian coordinates for scalar Concentration [SAFE-C]) and applied it to two CO₂ concentration towers in central Canada: the East Trout Lake 106-m-tall tower (54°21′N, 104°59′W) and the Candle Lake 28-m-high tower (53°59′N, 105°07′W). Results show that the ETL tower’s annual concentration footprints were around 10³–10⁵ km². The monthly footprint climatologies in summer were 1.5–2 times larger than in winter. The impacts of land surface carbon flux associated with heterogeneous distribution of vegetation types on the CO₂ concentration measurements were different for the different heights, varied with a range of ±5 % to ±10 % among four heights. This study indicates that concentration footprint climatology analysis is important in interpreting the seasonal, annual and inter-annual variations of tower measured CO₂ concentration data and is essential for comparing and scaling regional carbon flux estimates using top-down or bottom-up approaches.  相似文献   

Exploring the effect of meso‐scale shale beds on a reservoir's overall stress sensitivity to seismic waves     

Colin MacBeth  Yesser HajNasser  Karl Stephen  Andy Gardiner 《Geophysical Prospecting》2011,59(1):90-110

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