Origins and evolution of rhyolitic magmas in the central Snake River Plain: insights from coupled high-precision geochronology,oxygen isotope,and hafnium isotope analyses of zircon     

Dylan?P.?ColónEmail author  Ilya?N.?Bindeman  J?rn-Frederik?Wotzlaw  Eric?H.?Christiansen  Richard?A.?Stern 《Contributions to Mineralogy and Petrology》2018,173(2):11

We present new high-precision CA-ID-TIMS and in situ U–Pb ages together with Hf and O isotopic analyses (analyses performed all on the same grains) from four tuffs from the 15?10 Ma Bruneau–Jarbidge center of the Snake River Plain and from three rhyolitic units from the Kimberly borehole in the neighboring 10?6 Ma Twin Falls volcanic center. We find significant intrasample diversity in zircon ages (ranges of up to 3 Myr) and in δ¹⁸O (ranges of up to 6‰) and ε_Hf (ranges of up to 24 ε units) values. Zircon rims are also more homogeneous than the associated cores, and we show that zircon rim growth occurs faster than the resolution of in situ dating techniques. CA-ID-TIMS dating of a subset of zircon grains from the Twin Falls samples reveals complex crystallization histories spanning 10⁴–10⁶ years prior to some eruptions, suggesting that magma genesis was characterized by the cyclic remelting of buried volcanic rocks and intrusions associated with previous magmatic episodes. Age-dependent trends in zircon isotopic compositions show that rhyolite production in the Yellowstone hotspot track is driven by the mixing of mantle-derived melts (normal δ¹⁸O and ε_Hf) and a combination of Precambrian basement rock (normal δ¹⁸O and ε_Hf down to ??60) and shallow Mesozoic and Cenozoic age rocks, some of which are hydrothermally altered (to low δ¹⁸O values) by earlier stages of Snake River Plain magmatism. These crustal melts hybridize with juvenile basalts and rhyolites to produce the erupted rhyolites. We also observe that the Precambrian basement rock is only an important component in the erupted magmas in the first eruption at each caldera center, suggesting that the accumulation of new intrusions quickly builds an upper crustal intrusive body which is isolated from the Precambrian basement and evolves towards more isotopically juvenile and lower-δ¹⁸O compositions over time.  相似文献   

Snow interception modelling: Isolated observations have led to many land surface models lacking appropriate temperature sensitivities     

Jessica D. Lundquist  Susan Dickerson-Lange  Ethan Gutmann  Tobias Jonas  Cassie Lumbrazo  Dylan Reynolds 《水文研究》2021,35(7):e14274

When formulating a hydrologic model, scientists rely on parameterizations of multiple processes based on field data, but literature review suggests that more frequently people select parameterizations that were included in pre-existing models rather than re-evaluating the underlying field experiments. Problems arise when limited field data exist, when “trusted” approaches do not get reevaluated, and when sensitivities fundamentally change in different environments. The physics and dynamics of snow interception by conifers is just such a case, and it is critical to simulation of the water budget and surface albedo. The most commonly used interception parameterization is based on data from four trees from one site, but results from this field study are not directly transferable to locations with relatively warmer winters, where the dominant processes differ dramatically. Here, we combine a literature review with model experiments to demonstrate needed improvements. Our results show that the choice of model form and parameters can vary the fraction of snow lost through interception by as much as 30%. In most simulations, the warming of mean winter temperatures from −7 to 0°C reduces the modelled fraction of snow under the canopy compared to the open, but the magnitude of simulated decrease varies from about 10% to 40%. The range of results is even larger when considering models that neglect the melting of in-canopy snow in higher-humidity environments where canopy sublimation plays less of a role. Thus, we recommend that all models represent canopy snowmelt and include representation of increased loading due to increased adhesion and cohesion when temperatures rise from −3 to 0°C. In addition to model improvements, field experiments across climates and forest types are needed to investigate how to best model the combination of dynamically changing forest cover and snow cover to better understand and predict changes to albedo and water supplies.  相似文献   

Geophysical exploration for epithermal gold deposits   总被引：1，自引：0，他引：1  

R.J. Irvine  M.J. Smith 《Journal of Geochemical Exploration》1990,36(1-3)

Epithermal gold deposits are highly variable in form, ranging from thin quartz veins to large disseminated deposits, and are located in a variety of geological environments. Consequently, they exhibit a wide range of geophysical signatures. Hydrothermal alteration accompanying these deposits causes pronounced changes in the physical properties of the rocks. Magnetic susceptibility and remanence decrease; the potassium content commonly increases causing an increase in radioactivity; the electrical resistivity changes by up to two orders of magnitude; and the density increases or decreases depending on the nature of the host rock and alteration processes.Airborne magnetic surveys are effective in delineating major structures which may control the locations of epithermal gold deposits, and also in detecting magnetic lows or “flat zones” resulting from the destruction of magnetite by hydrothermal alteration. Radiometric surveys may detect potassium enrichment accompanying this alteration. Filtering and image-processing techniques are particularly useful in enhancing magnetic and radiometric data to reveal subtle structures and alteration systems.Ground geophysical techniques can play an important in defining drill targets. Well controlled gravity surveys may assist in the delineation of major structures, basement highs and alteration zones. Buried conductive alteration systems can be defined by resistivity, electromagnetic and magnetotelluric methods. Resistive gold-bearing silicified zones and shallow quartz vein systems are commonly detectable by conventional galvanic or inductive resistivity techniques.Geophysical surveys over a number of epithermal gold deposits are presented, including Bimurra-Conway (northeast Queensland, Australia), Gold Ridge (Solomon Islands), Ohui (Coromandel Peninsula, New Zealand), McLaughlin (California, USA), Rhyolite Creek (Victoria, Australia) and Mt Aubrey (New South Wales, Australia).Provided there is a clear appreciation of survey objectives and a good understanding of the changes in physical properties which rocks undergo during hydrothermal alteration, geophysics can make a substantial contribution to epithermal gold exploration.  相似文献   

A lithogeochemical approach to Stratigraphical problems at the Millstream potash deposit, New Brunswick, Canada     

S.J. Hoffman  K.S. Crosby  J.A. Irvine 《Journal of Geochemical Exploration》1987,28(1-3)

A lithogeochemical study was undertaken of the Millstream potash deposit, New Brunswick, Canada, a marine evaporite deposit with a complex depositional and tectonic history. The objective of the study was to determine if potash intersections in boreholes represent different geological horizons, or the same stratum repeated by folding or faulting. The deposit is found at a depth of 800–1000 m.Water-soluble and -insoluble fractions of drill core from five ore zones in four holes were analyzed using multielement ICP instrumentation following sequential hot water and aqua regia leaches. Meaningful variations in the data for the different ore zones were evident for eight elements in the water-soluble portion, and for seventeen elements in the water-insoluble residue. These results characterize a lowermost sylvinite unit which is relatively depleted in most elements, with the exception of Mg and Al in the residue. Regression analysis indicates a weak correlation between Fe and the common base metals, in contrast to the immediately overlying sylvinite unit which is relatively enriched in most elements, including Fe, but where Fe apparently exerts no control over the base metals. Cluster analysis confirms these two units are easily distinguished from each other. The upper two ore horizons are distinguishable from the lower units on the basis of different abundances of some elements, such as water-soluble B, and on the strong scavenging abilities of Fe on the common base metals.No single element is able to uniquely fingerprint a particular sylvinite horizon, but suites of elements are able to classify each horizon as geochemically distinctive. The results appear to confirm the validity of the geological correlations.  相似文献   

The Control Of Coherent Eddies In Vegetation Canopies: Streamwise Structure Spacing, Canopy Shear Scale And Atmospheric Stability   总被引：9，自引：9，他引：0  

Y. Brunet  M. R. Irvine 《Boundary-Layer Meteorology》2000,94(1):139-163

An analogy has been established between a plane mixing layer and the atmospheric flow near the top of a vegetation canopy. It is based on a common feature, a strong inflection in the mean velocity profile, responsible for hydrodynamical instabilities that set the pattern for the coherent eddies and determine the turbulence length scales. In an earlier study, this analogy was tested using a small data set from thirteen experiments, all in near-neutral conditions. It provided a good prediction of the streamwise spacing _w of the dominant canopy eddies (evaluated from time series of vertical velocity) that appears to depend on a shear length scale L_s = U(h)/U'(h), where h is canopy height, U is mean velocity and U' the vertical gradient dU/dz. The present analysis utilizes an extensive data set of approximately 700 thirty-minute runs, from six experiments on two forest sites and a maize crop, with a large range of stability conditions. _w was estimated for each run using the wavelet transform as an objective, automated detection method. First, the variations of _w and L_s with atmospheric stability are discussed. Neutral and unstable values exhibit a large scatter whereas in stable conditions both variables decrease with increasing stability. It is subsequently found that _w is directly related to L_s, in a way close to the neutral prediction _w /h = 8.1L_s/h.The Strouhal number S_tr = L_s /_w is then shown to vary with atmospheric stability, weakly in unstable conditions, more significantly in stable conditions. Altogether these results suggest that, to some extent, the plane mixing-layer analogy can be extended to non-neutral conditions. It is argued that the primary effect of atmospheric stability, at least in stable conditions, is to modify the shear length scale L_s through changes in U(h) and U'(h), which in turn determines the streamwise spacing of the active, coherent motions.  相似文献   

Torsional vibrations in boxgirder suspension bridges     

Max Irvine 《地震工程与结构动力学》1974,3(2):203-213

A linear theory is developed for the free, torsional vibrations of the single-span, boxgirder suspension bridge. Both symmetric and antisymmetric modes are considered. For the symmetric modes, which induce additional cable tension, it is shown that it is imperative to include the elasticity of the cables if correct solutions are to be obtained. Three examples of bridges with widely differing properties are presented to illustrate the applicability of the theory. Orthogonality of the torsional modes of vibration is proved in Appendix I and the modification to the analysis, required when rigid centre ties are present, is outlined in Appendix II. The theories presented herein can be readily extended to the three-span bridge.  相似文献   

Exploring Mobility Indoors: an Application of Sensor‐based and GIS Systems     

Anastasia Petrenko  Anton Sizo  Winchel Qian  A. Dylan Knowles  Amin Tavassolian  Kevin Stanley  Scott Bell 《Transactions in GIS》2014,18(3):351-369

The popularization of tracking devices, such as GPS, accelerometers and smartphones, have made it possible to detect, record, and analyze new patterns of human movement and behavior. However, employing GPS alone for indoor localization is not always possible due to the system's inability to determine location inside buildings or in places of signal occlusion. In this context, the application of local wireless networks for determining position is a promising alternative solution, although they still suffer from a number of limitations due to energy and IT‐resources. Our research outlines the potential for employing indoor wireless network positioning and sensor‐based systems to improve the collection of tracking data indoors. By applying various methods of GIScience we developed a methodology that can be applicable for diverse human indoor mobility analysis. To show the advantage of the proposed method, we present the result of an experiment that included mobility analysis of 37 participants. We tracked their movements on a university campus over the course of 41 days and demonstrated that their movement behavior can be successfully studied with our proposed method.  相似文献   

Use of GIS and dasymetric mapping for estimating tsunami-affected population to facilitate humanitarian relief logistics: a case study from Phuket,Thailand     

Jitt-Aer  Kiatkulchai  Wall  Graham  Jones  Dylan  Teeuw  Richard 《Natural Hazards》2022,113(1):185-211

Natural Hazards - The 2004 Indian Ocean tsunami led to improvements in Thailand’s early warning systems and evacuation procedures. However, there was no consideration of better aid delivery,...  相似文献   

Water Harvesting in Sub‐Saharan Africa edited by William Critchley and John Gowing (eds). Earthscan,Oxford and New York, 2013, pp. xv + 201 (ISBN: 978‐0‐415‐53773‐5) (hbk) (ISBN: 978‐0‐415‐53786‐5) (pbk).          下载免费PDF全文

Kenneth Irvine 《Singapore journal of tropical geography》2015,36(2):268-270

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Temporal Pointing Variations of the Solar Dynamics Observatory’s HMI and AIA Instruments on Subweekly Time Scales     

N. Brice Orange  Hakeem M. Oluseyi  David L. Chesny  Maulik Patel  Patrick Champey  Katie Hesterly  Dylan Anthony  Robert Treen 《Solar physics》2014,289(5):1901-1915

Achieving subarcsecond co-registration across varying time-lines of multi-wavelength and instrument images is difficult and requires an accurate characterization of the instrument pointing jitter. We investigated the internal pointing errors on daily and yearly time-scales that occur across the Solar Dynamics Observatory’s (SDO) Atmospheric Imaging Assembly (AIA) and Helioseismic Magnetic Imager (HMI). Using cross-correlation techniques on the AIA 1700 Å passband and the HMI line-of-sight magnetograms from three years of observational image pairs at approximately three-day intervals, internal pointing errors were quantified. Pointing variations of ±?0.26″ (jitter-limited) and ±?0.50″ in the solar East–West (x) and North–South (y) directions, respectively, were measured. AIA observations of the Venus transit in June 2012 were used to measure existing coalignment offsets in all passbands. We found that the AIA passband pointing variations are 〈ΔX _CO〉=1.10″±1.41″ and 〈ΔY _CO〉=1.25″±1.24″ when aligned to the HMI nominal image center, referred to here as the CutOut technique. Minimal long-term pointing variations found between limb and correlation derived pointings provide evidence that the image-center positions provided by the instrument teams achieve single-pixel accuracy on time scales shorter than their characterization. However, daily AIA passband pointing variations of ??1.18″ indicate that autonomous subarcsecond co-registration is not fully achieved yet.  相似文献