Harzburgite to lherzolite and back again: metasomatic processes in ultramafic xenoliths from the Wesselton kimberlite, Kimberley, South Africa   总被引：17，自引：1，他引：16  

W. L. Griffin  S. R. Shee  C. G. Ryan  T. T. Win  B. A. Wyatt 《Contributions to Mineralogy and Petrology》1999,134(2-3):232-250

Garnets from phlogopite harzburgite xenoliths from the Wesselton kimberlite show zoning from low-Ca harzburgitic cores to rims with lherzolitic Ca-Cr relations. Garnet cores are depleted in Y and HREE, but have sinuous REE patterns enriched in the MREE. Rimwards increase in Ca and decrease in Cr and Mg is accompanied by increases in Zr, Y, Ti and HREE. Secondary replacement rims on some garnets consist of garnet with low Ca and Cr, but high Mg, Ti and HREE. The zoning, and the secondary replacement rims, are attributed to different stages of a metasomatic process that has converted harzburgite to lherzolite, at temperatures near 1000 °C. Modelling of zoning profiles suggests that the process can be divided into three parts: (a) Inwards diffusion of Ca, Zr and Y over periods of 10,000–30,000 years, from a fluid depleted in Ti, Ga and Y; (b) formation of overgrowths high in Ca, Zr, Y and Ti, followed by annealing over periods of several thousand years; (c) formation of secondary reaction rims of low-Ca garnet, on very short timescales prior to eruption. The sinuous REE patterns of the garnet cores are regarded as “primary” features reflecting an ancient metasomatic event superimposed on a depleted protolith. The high Zr/Y, Zr/Ti and Zr/Ca of the fluids corresponding to stage (a) are ascribed to the presence of phlogopite and garnet in the matrix near the fluid source (presumed to be a melt, possibly a kimberlite precursor), leading to the development of concentration fronts in the percolating fluid. The overgrowths of stage (b) appear to coincide with the precipitation of phlogopite in the rock. The low Ca of the fluid responsible for the secondary replacement rims of stage (c) may reflect the late precipitation of clinopyroxene or Ca-carbonate as part of the metasomatic assemblage. These processes have significantly modified the modal, major- and trace-element composition of the mantle volume sampled by the Wesselton kimberlite, within <1 Ma of eruption. Recognition of such effects and their distribution in time and space is essential to understanding of the evolution of the subcontinental lithospheric mantle. Received: 11 February 1998 / Accepted: 24 June 1998  相似文献   

Reproduction of secondary data in projection pursuit transformation     

John?G.?ManchukEmail author  Ryan?M.?Barnett  Clayton?V.?Deutsch 《Stochastic Environmental Research and Risk Assessment (SERRA)》2017,31(10):2585-2605

A challenge when working with multivariate data in a geostatistical context is that the data are rarely Gaussian. Multivariate distributions may include nonlinear features, clustering, long tails, functional boundaries, spikes, and heteroskedasticity. Multivariate transformations account for such features so that they are reproduced in geostatistical models. Projection pursuit as developed for high dimensional data exploration can also be used to transform a multivariate distribution into a multivariate Gaussian distribution with an identity covariance matrix. Its application within a geostatistical modeling context is called the projection pursuit multivariate transform (PPMT). An approach to incorporate exhaustive secondary variables in the PPMT is introduced. With this approach the PPMT can incorporate any number of secondary variables with any number of primary variables. A necessary alteration to the approach to make this numerically practical was the implementation of a continuous probability estimator that relies on Bernstein polynomials for the transformation that takes place in the projections. Stopping criteria were updated to incorporate a bootstrap t test that compares data sampled from a multivariate Gaussian distribution with the data undergoing transformation.  相似文献   

Effect of seasonal flushing on nutrient export characteristics of an urbanizing,remote, ungauged coastal catchment   总被引：1，自引：0，他引：1  

Gayan L. Gunaratne  Ryan I.J. Vogwill 《水文科学杂志》2017,62(5):800-817

Urbanization is a primary driver of nutrient export in coastal catchments; however, estimating the rate of export from urbanizing, remote and ungauged communities with episodic rainfall characteristics has rarely been reported in tropical and subtropical areas. In this study, the coastal catchment of Roebuck Bay near Broome, northwestern Australia, was instrumented to elucidate the effect of seasonal flushing on nutrient export. A cost-effective framework involving temporary gauging and community participation led to a quantitative estimate of surface hydrology and nutrient dynamics from this urbanizing, remote and ungauged catchment. The contribution of nutrient export was larger from the older Broome town site sub-catchments compared to sub-catchments that have been progressively urbanized since 2000. A distinctive seasonal first flush phenomenon, with an initial 30% of runoff volume containing 40–70% of the nutrient load was a key feature. This indicates there are opportunities for storm-water management to minimize impacts through adopting water-sensitive urban design principles.  相似文献   

Method for estimating available groundwater volume of small coral islands     

Ryan T. Bailey  Saman Tavakoli Kivi 《水文科学杂志》2017,62(14):2381-2392

We present a simple modelling method to estimate the volume of available groundwater in the freshwater lens of atoll islands under steady-state conditions. Model inputs include annual rainfall depth, island width for cross-sections along the length of the island, aquifer hydraulic conductivity, and depth to the contact between the upper sand aquifer and the lower limestone aquifer. The methodology is tested for nine islands of varying size in the Maldives and Micronesia. Sensitivity analysis indicates that lens volume on large islands typically is governed by the depth to the discontinuity, whereas lens volume for smaller islands is governed by rainfall rate and hydraulic conductivity. Volume curves, which relate lens volume to lens thickness, are developed for each of the nine islands and for three generic island shapes to allow rapid estimation of lens volume given field-estimated lens thickness. The methods presented in this study can be used for any small atoll island.  相似文献   

Using Diurnal Temperature Signals to Infer Vertical Groundwater‐Surface Water Exchange          下载免费PDF全文

Dylan J. Irvine  Martin A. Briggs  Laura K. Lautz  Ryan P. Gordon  Jeffrey M. McKenzie  Ian Cartwright 《Ground water》2017,55(1):10-26

Heat is a powerful tracer to quantify fluid exchange between surface water and groundwater. Temperature time series can be used to estimate pore water fluid flux, and techniques can be employed to extend these estimates to produce detailed plan‐view flux maps. Key advantages of heat tracing include cost‐effective sensors and ease of data collection and interpretation, without the need for expensive and time‐consuming laboratory analyses or induced tracers. While the collection of temperature data in saturated sediments is relatively straightforward, several factors influence the reliability of flux estimates that are based on time series analysis (diurnal signals) of recorded temperatures. Sensor resolution and deployment are particularly important in obtaining robust flux estimates in upwelling conditions. Also, processing temperature time series data involves a sequence of complex steps, including filtering temperature signals, selection of appropriate thermal parameters, and selection of the optimal analytical solution for modeling. This review provides a synthesis of heat tracing using diurnal temperature oscillations, including details on optimal sensor selection and deployment, data processing, model parameterization, and an overview of computing tools available. Recent advances in diurnal temperature methods also provide the opportunity to determine local saturated thermal diffusivity, which can improve the accuracy of fluid flux modeling and sensor spacing, which is related to streambed scour and deposition. These parameters can also be used to determine the reliability of flux estimates from the use of heat as a tracer.  相似文献   

Response of hybrid isolation system during a shake table experiment of a full‐scale isolated building          下载免费PDF全文

Keri L. Ryan  Taichiro Okazaki  Camila B. Coria  Eiji Sato  Tomohiro Sasaki 《地震工程与结构动力学》2018,47(11):2214-2232

A full‐scale 5‐story steel moment frame building was subjected to a series of earthquake excitations using the E‐Defense shake table in August, 2011. For one of the test configurations, the building was seismically isolated by a hybrid system of lead‐rubber bearings and low friction roller bearings known as cross‐linear bearings, and was designed for a very rare 100 000‐year return period earthquake at a Central and Eastern US soil site. The building was subject to 15 trials including sinusoidal input, recorded motions and simulated earthquakes, 2D and 3D input, and a range of intensities including some beyond the design basis level. The experimental program was one of the first system‐level full‐scale validations of seismic isolation and the first known full‐scale experiment of a hybrid isolation system incorporating lead‐rubber and low friction bearings. Stable response of the hybrid isolation system was demonstrated at displacement demands up to 550 mm and shear strain in excess of 200%. Torsional amplifications were within the new factor stipulated by the code provisions. Axial force was observed to transfer from the lead‐rubber bearings to the cross‐linear bearings at large displacements, and the force transfer at large displacements exceeded that predicted by basic calculations. The force transfer occurred primarily because of the flexural rigidity of the base diaphragm and the larger vertical stiffness of the cross‐linear bearings relative to the lead‐rubber bearings.  相似文献   

Fine mesh screening of midden material and the recovery of fish bone: The development of flotation and deflocculation techniques for an efficient and effective procedure     

Anne Ross  Ryan Duffy 《Geoarchaeology》2000,15(1):21-41

The absence of fish remains in archaeological sites in Moreton Bay, southeast Queensland, Australia, may be a function of recovery techniques, rather than a reflection of resource paucity and late onset of occupation, as has been posited in archaeological literature. An excavation on Peel Island in Moreton Bay was devised, in part, to test this proposition, and a 1‐mm mesh screen was used to enhance recovery. But sorting this fine fraction took 20 h. In this article we outline experiments to find a more efficient and effective technique for sieving and sorting fine fraction archaeological deposits, using methods borrowed from soil science. We show how sorting time can be reduced to 2 h 30 min per 100 g sample and argue that the vast increase in knowledge about the site occurring as a result of using the very fine mesh sieve warrants the continued application of these laboratory methods. © 2000 John Wiley & Sons, Inc.  相似文献   

Groundwater for People and the Environment: A Globally Threatened Resource     

Hugo A. Loaiciga  Ryan Doh 《Ground water》2024,62(3):332-340

The intensity of global groundwater use rose from 124 m³ per capita in 1950 to 152 m³ in 2021, for a 22.6% rise in the annual per capita use. This rise in global per capita water use reflects rising consumption patterns. The global use of groundwater, which provides between 21% and 30% of the total freshwater annual consumption, will continue to expand due to the sustained population growth projected through most of the 21st century and the important role that groundwater plays in the water-food-energy nexus. The rise in groundwater use, on the other hand, has inflicted adverse impacts in many aquifers, such as land subsidence, sea water intrusion, stream depletion, and deterioration of groundwater-dependent ecosystems, groundwater-quality degradation, and aridification. This paper projects global groundwater use between 2025 and 2050. The projected global annual groundwater withdrawal in 2050 is 1535 km³ (1 km³ = 10⁹ m³ = 810,713 acre-feet). The projected global groundwater depletion, that is, the excess of withdrawal over recharge, in 2050 equals 887 km³, which is about 61% larger than in 2021. This projection signals probable exacerbation of adverse groundwater-withdrawal impacts, which are worsened by climatic trends and the environmental requirement of groundwater flow unless concerted national and international efforts achieve groundwater sustainability.  相似文献   

Decadal and seasonal changes in landcover at Padre Island: Implications for the role of the back-barrier in signaling island state change     

Kenton R. Fisher  Ryan C. Ewing  Orencio Duran Vinent 《地球表面变化过程与地形》2023,48(1):163-178

Long-term and seasonal geomorphological changes at Padre Island, Texas are identified and linked with potential external drivers. Aerial and satellite images from 1950 to 2018, monthly images from 2019 to 2020, and a 2018 LiDAR data set are used to assess long-term and seasonal geomorphological changes within a 50 km² area of Padre Island near Port Mansfield, Texas. Trends in landcover are evaluated by mapping and comparing the relative areal coverage of each facies. Vegetated dunes, absent initially, emerged in the fore-island and expanded into the back-barrier to cover 14% of the study area. The active vegetation-free back-barrier dune field steadily decreased in areal extent from 12% to 6% as vegetation spread. Nebkha dune coverage fluctuated between 4% and 7%. Expansive microbial mats colonized the wind tidal and deflation flats surrounding the vegetated dunes and back-barrier dune field giving rise to a remarkably different landscape over the 50-year period studied. An assessment of external forcing factors identifies increased rates of relative sea level rise and decreased sediment influx as the most likely primary factors driving the geomorphological changes. These changes have induced a widespread shift toward stabilization of island sediments by vegetation and microbial mats, which in turn has starved the back-barrier of sediments resulting in low rates of accretion and increased flooding. These findings highlight the sensitivity of the back-barrier and, in particular, the dune facies to changes in sea level and sediment supply, and show that microbial mats are effective at stabilizing island sediments and may be harbingers to barrier island response to rising sea level. As shown in this study, long-term monitoring of geomorphic facies changes and topography can detect important shifts in the island state that can be used to inform decision making for these sensitive coastal landscapes.  相似文献   

How ready is ready? Measuring physical preparedness for severe storms     

Ryan  Barbara  King  Rachel 《Natural Hazards》2020,104(1):171-199

This paper investigates use of inventories, or checklists of activities, as an emergency management tool to motivate preparedness action in individuals. It develops the inventory concept to provide the foundation for a more targeted approach to storm preparation communication and community engagement. It also examines the potential efficacy of alternatives to paper-based checklists, such as web or smartphone applications. Academic and grey literature was reviewed to collect activities for a storm inventory for emergency agencies to measure individual preparedness and for individuals to measure their preparation progress. The resulting master list was refined for application and tested for useability in a pilot study of semi-structured interviews in a storm-susceptible community in Queensland, Australia. Also, clustering items by type of preparedness activity reveal where strengths and weaknesses exist in individual preparedness. For instance, preparation for leaving and safety planning were shown to be the areas of weakest activity in the pilot sample, while preparation of the house for a storm was the strongest area. In addition, behaviour change literature shows potential for effective use of an inventory-based smartphone application in motivating preparation activity. Data collected by a storm preparedness smartphone application could show where a communication or engagement program for targeted communities should be focused. It is supported by health literature that identifies preferences of individuals to make progress on complex tasks in stages, the value of lists to achievement of goals and demonstrated increase in uptake of activities prompted by smartphone applications over web or paper-based diaries.

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