An Embedded Model Estimator for Non-Stationary Random Functions Using Multiple Secondary Variables     

Daly  Colin 《Mathematical Geosciences》2022,54(5):979-1015

Mathematical Geosciences - An algorithm for non-stationary spatial modelling using multiple secondary variables is developed herein, which combines geostatistics with quantile random forests to...  相似文献   

Thermal expansion and decomposition of jarosite: a high-temperature neutron diffraction study     

Hongwu Xu  Yusheng Zhao  Sven C. Vogel  Donald D. Hickmott  Luke L. Daemen  Monika A. Hartl 《Physics and Chemistry of Minerals》2010,37(2):73-82

The structure of deuterated jarosite, KFe₃(SO₄)₂(OD)₆, was investigated using time-of-flight neutron diffraction up to its dehydroxylation temperature. Rietveld analysis reveals that with increasing temperature, its c dimension expands at a rate ~10 times greater than that for a. This anisotropy of thermal expansion is due to rapid increase in the thickness of the (001) sheet of [Fe(O,OH)₆] octahedra and [SO₄] tetrahedra with increasing temperature. Fitting of the measured cell volumes yields a coefficient of thermal expansion, α = α₀ + α₁ T, where α₀ = 1.01 × 10⁻⁴ K⁻¹ and α₁ = −1.15 × 10⁻⁷ K⁻². On heating, the hydrogen bonds, O1···D–O3, through which the (001) octahedral–tetrahedral sheets are held together, become weakened, as reflected by an increase in the D···O1 distance and a concomitant decrease in the O3–D distance with increasing temperature. On further heating to 575 K, jarosite starts to decompose into nanocrystalline yavapaiite and hematite (as well as water vapor), a direct result of the breaking of the hydrogen bonds that hold the jarosite structure together.  相似文献   

Zircon texture and chemical composition as a guide to magmatic processes and mixing in a granitic environment and coeval volcanic system   总被引：3，自引：0，他引：3  

Damien Gagnevin  J. Stephen Daly  Andreas Kronz 《Contributions to Mineralogy and Petrology》2010,159(4):579-596

This study documents the chemical and textural responses of zircon in the Elba igneous complex, with particular reference to the 7- to 7.8-Ma-old Monte Capanne pluton in relation to its coeval volcanic counterpart (Capraia), using BSE imaging and quantitative electron microprobe analyses. The Monte Capanne pluton displays multiple field and geochemical evidence for magma mixing. The samples we have investigated (including monzogranitic, mafic enclave and dyke samples) display similar zircon textures and are associated with an extremely large range of trace and minor element (Hf, Y, HREE, Th, U) compositions, which contrast with relatively simple textures and zoning patterns in zircons from a Capraia dacite. We have used a relatively simple textural classification (patchy zoning, homogenous cores, oscillatory zoning and unzoned zircon) as the basis for discussing the chemical composition and chemical variation within zircons from the Monte Capanne pluton. Based on these data and other works (Dini et al. 2004 in Lithos 78:101–118, 2004) , it is inferred that mixing between metaluminous and peraluminous melts occurred early in the evolution of the Monte Capanne magma chamber. In particular, mixing was responsible for the development of the patchy-zoning texture in the zircon cores, which was associated with reactions between other accessory phases (including monazite, apatite, allanite), which we infer to have significantly affected the Th distribution in zircon. Zircons from the MC pluton displaying “homogeneous cores” have chemical affinities with zircons in the coeval Capraia volcanic system, consistent with the participation of a Capraia-like mantle end-member during mixing. Further zircon growth in the MC pluton produced the oscillatory zoning texture, which records both long-term (crystal fractionation) and transient (recharge with both silicic and mafic magmas) events in a hybrid magma chamber. It is inferred that Hf and the Th/U ratio cannot be used alone to infer magmatic processes due to their dependency on temperature, nor are they a diagnostic feature of xenocrystic grains. This study shows that zircon chemistry coupled with detailed textural analysis can provide a powerful tool to elucidate the complex evolution of a magma system.  相似文献   

Tidally oscillating bisulfide fluxes and fluid flow rates observed with in situ chemical sensors at a warm spring in Monterey Bay,California     

Josh N. Plant  Kenneth S. Johnson  Steve E. Fitzwater  Carole M. Sakamoto  Luke J. Coletti  Hans W. Jannasch 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(12):1585-1595

An In Situ Ultraviolet Spectrophotometer (ISUS) was coupled to a benthic chamber to characterize the bisulfide flux emanating from a warm spring at the Extrovert Cliff locality within Monterey Bay, California. The chamber was periodically flushed with bottom seawater to reset chemical concentrations, which enabled deployments over multiple days. Data from several deployments, each lasting at least 10 days, were used to calculate flow rates, fluid concentrations, and fluxes over time. The bisulfide concentration of the fluid entering the chamber varied from 75 to 4500 μmol l^?1. Positive temperature anomalies up to 3.5° were associated with these elevated concentrations. Linear flow rates ranged from 2 to >17 m day^?1, while the bisulfide fluxes varied from 0.2 to 80 mol m^?2 day^?1. The bisulfide originated at depth and was not produced in the surface sediments via an anaerobic oxidation of methane coupled to sulfate reduction. Tides modulated the flow as well as the composition of the fluid entering the chamber. It appeared that a deep sourced fluid, which supplied the bisulfide, was mixed with a second, ambient seawater-like fluid before entering the flux chamber. At low tides, flow rates were at their highest and the contribution of the deep sourced fluid to the fluid entering the chamber was at a maximum.  相似文献   

Geological setting and SHRIMP U–Pb geochronological evidence for ca. 2680–2660 Ma lode-gold mineralization at Jundee–Nimary in the Yilgarn Craton, Western Australia     

Christopher J. Yeats  Ernst A. Kohler  Neal J. McNaughton  Luke J. Tkatchyk 《Mineralium Deposita》2001,36(2):125-136

The 7 million oz. Jundee–Nimary lode-gold deposit occurs in the northern portion of the Yandal greenstone belt in the northeastern part of the Archean Yilgarn Craton of Western Australia. Gold mineralization at Jundee–Nimary is similar in structural style, mineralogy, geochemistry and relative timing with respect to deformation and metamorphism, to other Western Australian Archean greenstone-hosted gold deposits, but is unusual in the fact that mineralized structures are crosscut by structurally late intermediate to felsic dykes. Within the Deakin South open cut, gold mineralization is hosted in brittle–ductile shear zones primarily developed within the dacitic Mitchell Porphyry. The Moore Porphyry, a broad dyke of porphyritic granodiorite, intrudes the Mitchell Porphyry, crosscutting and post-dating gold mineralization. Analytically indistinguishable SHRIMP U–Pb zircon ages of 2678 ± 5 Ma for the Mitchell Porphyry and 2669 ± 7 Ma for the Moore Porphyry require that gold mineralization at Jundee–Nimary occurred at ca. 2680–2660 Ma, approximately 40 million years earlier than the majority of published robust ages for gold mineralization in the Yilgarn Craton, which mostly overlap at ca. 2640–2630 Ma. The close spatial and temporal relationship between gold mineralization and felsic to intermediate magmatism at Jundee–Nimary also raises the possibility of a genetic link between hydrothermal and igneous activity. However, additional work is required to establish a firm connection. Current research on lode-gold mineralization in Archean, Paleozoic and Phanerozoic terranes suggests a model which postulates that these deposits formed during transpressional to compressional deformation in accretionary and collisional orogens and that their formation is intimately related to orogenic processes. Consequently, mineralization and regional metamorphism are expected to be diachronous, as terranes are accreted and the front of orogenesis migrates. Consideration of the new data presented in this paper in conjunction with previously published dates supports the hypothesis that gold mineralization, along with regional metamorphism, was generally diachronous from northeast to southwest across the Yilgarn Craton, over a period of approximately 40 million years from ca. 2680–2660 Ma to ca. 2640–2630 Ma. This is directly analogous to the accepted model for the timing of orogenic lode-gold mineralization in other provinces and therefore provides further support for a unified model for this style of deposit through geological time. Received: 17 March 2000 / Accepted: 8 September 2000  相似文献   

Two Dimensional Wavelet Analysis Applied to Geoid Anomalies Mixing and High Rayleigh Number Mantle Convection     

Luke Vecsey  Cathy Hier  Dave Yuen  Erik Sevre 《Visual Geosciences》2001,6(3):1-6

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Smithsonian Institution''s Global Volcanism Network     

Luke Jensen 《Bulletin of Volcanology》2001,63(4):293-294

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Intercomparison of Himawari-8 AHI-FSA with MODIS and VIIRS active fire products   总被引：1，自引：0，他引：1  

Chathura Wickramasinghe  Luke Wallace  Karin Reinke  Simon Jones 《International Journal of Digital Earth》2020,13(4):457-473

ABSTRACT

The AHI-FSA (Advanced Himawari Imager - Fire Surveillance Algorithm) is a recently developed algorithm designed to support wildfire surveillance and mapping using the geostationary Himawari-8 satellite. At present, the AHI-FSA algorithm has only been tested on a number of case study fires in Western Australia. Initial results demonstrate potential as a wildfire surveillance algorithm providing high frequency (every 10 minutes), multi-resolution fire-line detections. This paper intercompares AHI-FSA across the Northern Territory of Australia (1.4 million km²) over a ten-day period with the well-established fire products from LEO (Low Earth Orbiting) satellites: MODIS (Moderate Resolution Imaging Spectroradiometer) and VIIRS (Visible Infrared Imaging Radiometer Suite). This paper also discusses the difficulties and solutions when comparing high temporal frequency fire products with existing low temporal resolution LEO satellite products. The results indicate that the multi-resolution approach developed for AHI-FSA is successful in mapping fire activity at 500?m. When compared to the MODIS, daily AHI-FSA omission error was only 7%. High temporal frequency data also results in AHI-FSA observing fires, at times, three hours before the MODIS overpass with much-enhanced detail on fire movement.  相似文献   

Determination d'un nouveau pole paleomagnetique africain sur des formations cambriennes du Maroc     

L. Daly  J.P. Pozzi 《Earth and Planetary Science Letters》1977,34(2):264-272

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Rare earth element geochemistry of Late Devonian reefal carbonates, Canning Basin, Western Australia: confirmation of a seawater REE proxy in ancient limestones   总被引：6，自引：0，他引：6  

Luke D Nothdurft  Gregory E Webb 《Geochimica et cosmochimica acta》2004,68(2):263-283

Rare earth element and yttrium (REE+Y) concentrations were determined in 49 Late Devonian reefal carbonates from the Lennard Shelf, Canning Basin, Western Australia. Shale-normalized (SN) REE+Y patterns of the Late Devonian samples display features consistent with the geochemistry of well-oxygenated, shallow seawater. A variety of different ancient limestone components, including microbialites, some skeletal carbonates (stromatoporoids), and cements, record seawater-like REE+Y signatures. Contamination associated with phosphate, Fe-oxides and shale was tested quantitatively, and can be discounted as the source of the REE+Y patterns. Co-occurring carbonate components that presumably precipitated from the same seawater have different relative REE concentrations, but consistent REE+Y patterns. Clean Devonian early marine cements (n = 3) display REE+Y signatures most like that of modern open ocean seawater and the highest Y/Ho ratios (e.g., 59) and greatest light REE (LREE) depletion (average Nd_SN/Yb_SN = 0.413, SD = 0.076). However, synsedimentary cements have the lowest REE concentrations (e.g., 405 ppb). Non-contaminated Devonian microbialite samples containing a mixture of the calcimicrobe Renalcis and micritic thrombolite aggregates in early marine cement (n = 11) have the highest relative REE concentrations of tested carbonates (average total REE = 11.3 ppm). Stromatoporoid skeletons, unlike modern corals, algae and molluscs, also contain well-developed, seawater-like REE patterns. Samples from an estuarine fringing reef have very different REE+Y patterns with LREE enrichment (Nd_SN/Yb_SN > 1), possibly reflecting inclusion of estuarine colloidal material that contained preferentially scavenged LREE from a nearby riverine input source. Hence, Devonian limestones provide a proxy for marine REE geochemistry and allow the differentiation of co-occurring water masses on the ancient Lennard Shelf. Although appropriate partition coefficients for quantification of Devonian seawater REE concentrations from out data are unknown, hypothetical Devonian Canning Basin seawater REE patterns were obtained with coefficients derived from modern natural proxies and experimental values. Resulting Devonian seawater patterns are slightly enriched in LREE compared to most modern seawaters and suggest higher overall REE concentrations, but are very similar to seawaters from regions with high terrigenous inputs. Our results suggest that most limestones should record important aspects of the REE geochemistry of the waters in which they precipitated, provided they are relatively free of terrigenous contamination and major diagenetic alteration from fluids with high, non-seawater-like REE contents. Hence, we expect that many other ancient limestones will serve as seawater REE proxies, and thereby provide information on paleoceanography, paleogeography and geochemical evolution of the oceans.  相似文献