Atypical stratiform sulfide-poor platinum-group element mineralisation in the Agnew – Wiluna Belt komatiites,Wiluna, Western Australia     

M. L. Fiorentini  S. W. Beresford  B. Grguric  S. J. Barnes  W. E. Stone 《Australian Journal of Earth Sciences》2013,60(6):801-824

A new style of komatiite-associated sulfide-poor platinum-group element (PGE: Os, Ir, Ru, Rh, Pt, Pd) mineralisation has been identified at Wiluna in the strongly nickel sulfide (NiS) mineralised Agnew – Wiluna Greenstone Belt, Western Australia. The komatiite sequence at Wiluna is ～200 m thick and comprises a basal pyroxenite layer, a thick ortho-to-mesocumulate-textured peridotite core, which is overlain by rhythmically layered wehrlite, oikocrystic pyroxenite and thick upper gabbroic margins. Pegmatoid and dendritic (harrisitic) domains are common features, whereas spinifex-textured horizons and flow-top breccias are absent. The presence of anomalous PGE-enriched horizons (ΣPt – Pd = 200 – 500 ppb) in the oikocrystic pyroxenite and in the layered melagabbro and gabbronorite horizons directly overlying the wehrlite unit is due to the presence of fine-grained (1 – 10 μm) platinum-group minerals (PGMs). More than 70 PGM grains were identified, and a considerable mineralogical variability was constrained. However, only Pd – Pt-bearing phases were identified, whereas no Ir – Ru-bearing PGMs were found in any of the sections examined. Interestingly, all PGMs are not in paragenetic association with sulfides, and only sulfide-poor/free intervals contain significant PGM concentrations. The whole-rock PGE sequence largely reflects the PGM distribution. It is hypothesised that the Pd – Pt enrichment in the oikocrystic pyroxenite and melagabbros and the overall Ir – Ru depletion in the upper mafic section of the sequence are the result of extensive olivine and chromite crystallisation in the basal ultramafic section. PGE saturation was driven by extensive crystallisation of silicate and oxide phases in a sulfide-undersaturated environment. The crystallisation of clinopyroxene in the oikocrystic pyroxenite horizon may have triggered the formation of Pt – Pd-bearing alloys and arsenides, which were the first PGMs to form. Stratiform sulfide-poor PGE mineralisation at Wiluna is more similar in stratigraphic setting, style and composition to PGE-rich sulfide-poor mineralisation zones in thick differentiated intrusions, rather than to other PGE-enriched zones in komatiite-hosted systems, where PGE enrichment is directly associated with accumulations of magmatic sulfides.  相似文献   

Glacial isostatic adjustment in 3-D earth models: Implications for the analysis of tide gauge records along the U.S. east coast     

Jonathan E. Davis  Konstantin Latychev  Jerry X. Mitrovica  Roblyn Kendall  Mark E. Tamisiea 《Journal of Geodynamics》2008,46(3-5):90

Tide gauge records of recent sea-level change along the U.S. east coast have received significant attention within the literature of glacial isostatic adjustment (GIA). Geographic trends in these tide gauge rates are not reduced by a GIA correction based on a commonly adopted radial viscosity profile (characterized, in particular, by a lower mantle viscosity 1−2×10²¹ Pa s), and this has led to speculation that the residual trends reflect contributions from neotectonics or oceanographic processes. While the trends can be significantly reduced by adopting an Earth model with a stiffer lower mantle, such a model appears to be incompatible with independent constraints from post-glacial decay times in Hudson Bay. We use a finite-element model of the GIA process to investigate whether 3-D viscosity variations superimposed onto the “common” radial viscosity profile may provide a route to reconciling the east coast sea-level trends. We find that the specific 3-D structure we impose has little impact on the geographic trends in the GIA-corrected rates. However, we do find that the imposed lateral variations in lower mantle viscosity introduce a nearly uniform upward shift of 0.5 mm/yr in GIA-induced sea-level rates along the U.S. east coast. Thus, inferences of regional (U.S. east coast) sea-level rise due to modern melting of ice reservoirs, based on tide gauge rates corrected using 1-D GIA models, may be significantly biased by this simplifying assumption.  相似文献   

The line-of-sight velocity distributions of simulated merger remnants     

George J. Bendo  Joshua E. Barnes 《Monthly notices of the Royal Astronomical Society》2000,316(2):315-325

We use Gauss–Hermite functions to study the line-of-sight velocity distributions in simulated merger remnants. Our sample contains 16 remnants; eight produced by mergers between disc galaxies of equal mass, and eight produced by mergers between disc galaxies with mass ratios of 3:1. The equal-mass mergers display a wide range of kinematic features, including counterrotation at large radii, orthogonally rotating cores and misaligned rotational axes. Most of the unequal-mass remnants exhibit fairly regular disc-like kinematics, although two have kinematics more typical of the equal-mass remnants. Our results may be compared with observations of early-type objects, including ellipticals with misaligned kinematic axes, counterrotating systems and S0 galaxies.  相似文献   

Oceanography of the South Pacific, 1972: Papers presented at an international symposium held in Wellington,New Zealand, 9–15 February 1972. New Zealand National Commission for UNESCO,Wellington, 1973, 524 pp     

H. Barnes 《Marine Geology》1974,17(2):61-62

  相似文献   

Adding bounds to kriging     

Randal J. Barnes  Kwangho You 《Mathematical Geology》1992,24(2):171-176

The ordinary kriging interpolation algorithm is extended by the inclusion of explicit lower and upper bounds on the estimate. The associated estimation variance is written as the ordinary kriging variance plus a non-negative correction term.  相似文献   

Influences of the unsaturated,saturated, and riparian zones on the transport of nitrate near the Merced River,California, USA   总被引：1，自引：0，他引：1  

Joseph L. Domagalski  Steven P. Phillips  E. Randall Bayless  Celia Zamora  Carol Kendall  Richard A. WildmanJr  Janet G. Hering 《Hydrogeology Journal》2008,16(4):675-690

Transport and transformation of nitrate was evaluated along a 1-km groundwater transect from an almond orchard to the Merced River, California, USA, within an irrigated agricultural setting. As indicated by measurements of pore-water nitrate and modeling using the root zone water quality model, about 63% of the applied nitrogen was transported through a 6.5-m unsaturated zone. Transport times from recharge locations to the edge of a riparian zone ranged from approximately 6 months to greater than 100 years. This allowed for partial denitrification in horizons having mildly reducing conditions, and essentially no denitrification in horizons with oxidizing conditions. Transport times across a 50–100-m-wide riparian zone of less than a year to over 6 years and more strongly reducing conditions resulted in greater rates of denitrification. Isotopic measurements and concentrations of excess N₂ in water were indicative of denitrification with the highest rates below the Merced River. Discharge of water and nitrate into the river was dependent on gradients driven by irrigation or river stage. The results suggest that the assimilative capacity for nitrate of the groundwater system, and particularly the riverbed, is limiting the nitrate load to the Merced River in the study area.  相似文献   

American pragmatism: Towards a geographical introduction   总被引：1，自引：0，他引：1  

Trevor J. Barnes 《Geoforum》2008,39(4):1542-1554

The purposes of the paper are to provide a historical and thematic review of some of the variants of American philosophical pragmatism (old and new), and to point to its potential relevance for geography. The paper is divided into three sections. The first, discusses the origins of American pragmatism focussing on four figures: John Dewey, Oliver Wendell Holmes, William James, and Charles Sanders Peirce. Following the argument of Louis Menand (2001) in The Metaphysical Club, I will suggest that pragmatism took on its peculiar American character as a response to the deep fissures and wounds caused by that country’s Civil War. That war produced a loss of faith, undermining notions of universal progress and absolute truth. Pragmatism was the reaction. The second section brings pragmatism to the present, by focussing on three connected contemporary American pragmatists: Richard Rorty, Richard Bernstein, and Richard Shusterman. The hallmark of their work, and which justifies treating them as a group, is a willingness to stretch pragmatism: first, by making linkages with other anti-foundational, practice-based philosophical traditions, especially those within Continental European philosophy, and which had been shut out of Anglo-American philosophy after the Second World War by the rise of analytic philosophy; and second, by applying pragmatist ideas to issues like the body and popular culture to which it had never been applied. Finally, in the conclusion the paper reflects on the prospects of tethering pragmatism to the work of human geographers. Given the anti-architectonic impulses of pragmatism, such a project cannot simply be one of holus-bolus transferring pragmatism to geography. A different approach is needed, and which is schematically outlined and briefly illustrated using the idea of place.  相似文献   

The development of a non-linear autoregressive model with exogenous input (NARX) to model climate-water clarity relationships: reconstructing a historical water clarity index for the coastal waters of the southeastern USA     

Lee  Cameron C.  Sheridan  Scott C.  Barnes  Brian B.  Hu  Chuanmin  Pirhalla  Douglas E.  Ransibrahmanakul  Varis  Shein  Karsten 《Theoretical and Applied Climatology》2017,130(1-2):557-569

Theoretical and Applied Climatology - The coastal waters of the southeastern USA contain important protected habitats and natural resources that are vulnerable to climate variability and singular...  相似文献   

J. G. Calvert, R. Atkinson, J. A. Kerr, S. Madronich, G. K. Moortgat, T. J. Wallington, and G. Yarwood: The Mechanisms of Atmospheric Oxidation of the Alkenes     

Ian Barnes 《Journal of Atmospheric Chemistry》2001,39(3):328-330

  相似文献   

A study of two mid-crustal bright spots from southeast Georgia (USA)     

Arthur E. Barnes  Timothy J. Reston 《Geophysical Journal International》1992,108(2):683-691

  相似文献