Platinum-Group Element and Rhenium Concentrations in Low Abundance Reference Materials     

Thomas Meisel  Johann Moser 《Geostandards and Geoanalytical Research》2004,28(2):233-250

One or two gram aliquots of twelve reference materials with low platinum-group element (PGE) abundances (Ir concentrations ranging from 30 to 510 pg g^-1) were analysed by isotope dilution ICP-MS using an on-line chromatographic matrix separation after acid digestion in a high pressure asher (HPA-S) to determine the concentrations of Ru, Pd, Re, Ir and Pt. Osmium concentrations were determined via ID-ICP-MS but as volatile OsO₄, whereas Rh concentrations were calculated by comparing the peak areas of the chromatographic peak with that of a standard solution. Validation of the method was performed and the concepts of traceability and measurement uncertainty were applied to assure comparability. The reference materials BCR-2, BHVO-1, BHVO-2, BIR-1, DNC-1, EN026 10D-3, MAG-1, RGM-1, SCo-1, SDO-1, TDB-1 and W-2 were investigated to test for their usefulness for certification. The use of TDB-1 is highly recommended because it is homogeneous at the two gram level and many values based on several different analytical procedures have been published. It is recommended that our efforts should focus on the certification of this reference material to reduce the uncertainties of its currently certified values (Pd and Pt only) and to assign certified values to the other PGE and Re. It is necessary to have at least one well-characterised RM for validation of methods applied to the analysis of PGE and Re in low abundance samples, although the matrix of TDB-1 might not completely match those of many samples.  相似文献   

Thermal interaction between lava lobes     

Dorothee J. Burkhard 《Bulletin of Volcanology》2003,65(2-3):136-143

  相似文献   

Worm holes and their space-time continuum: Spatial and temporal variability of macroinfaunal annelids in a Northern New England salt marsh     

David S. Johnson  John W. Fleeger  Kari A. Galván  E. Barry Moser 《Estuaries and Coasts》2007,30(2):226-237

Coastal systems serve many human uses and as a result are susceptible to anthropogenic activities such as nutrient loading and overfishing. In soft sediments, infauna frequently serve as key indicators of such activities. To use infauna effectively as bioindicators, it is important to understand how infaunal abundances and community patterns vary naturally within ecosystems. We examined the spatial and temporal dynamics of infaunal annelids in four tidal creeks of the Plum Island Estuary, Massachusetts, USA, from June to October 2003, sampling along a tidal inundation gradient that crossed five distinct habitats from creek bottoms to the vegetated high marsh platform. Annelids comprised 97% of the total number of macroinfauna. Highest densities were found in creek wall habitats (33,418–65,535 individuals m⁻²), and lowest densities (2,421–10,668 individuals m⁻²) were found inSpartina patens habitats. Five numerically abundant species comprised 87% of the annelid assemblage and three species,Manayunkia aestuarina (Polychaeta),Paranais litoralis (Oligochaeta), andCernosvitoviella immota (Oligochaeta), were broadly distributed across the marsh landscape.Streblospio benedicti (Polychaeta) andFabricia sabella (Polychaeta) were abundant only in mudflat and creek wall habitats, respectively.P. litoralis experienced a summer decline in all habitats, whereasM. aestuarina abundance increased 4–5 fold, in October relative to June in creek wall and tall-formSpartina alterniflora habitats. Hierarchical spatial, analysis revealed that >90% of the variability in annelid abundances was found at the mesospatial scale (<50 m). Variation among the four creeks, (>1 km) was relatively small.  相似文献   

Surface alteration of basalt due to cation-migration     

Dorothee J. M. Burkhard  Hiltrud Müller-Sigmund 《Bulletin of Volcanology》2007,69(3):319-328

Basaltic lava from Kilauea, Hawaii may have a red-brown surface, indicative of Fe-(hydr)oxides. This surface is not found where exposed to weathering, but at the interface between lava lobes, or in the interior of lava channels. We use several analytical techniques to determine how these Fe-(hydr)oxide surfaces may have developed. WDS-elemental distribution line profiles from the lava surface towards the lava′s interior detect an Fe-rich film of less than 5 μm thickness. Heat treatment of quenched, fresh lava samples of the same chemical composition between 600–1,090°C helps to replicate temperatures under which such an Fe-rich film might have formed. These experiments suggest that Fe-enrichment occurs above 1,020°C, whereas at lower temperatures Ca is enriched relative to Fe. One sample was treated below the glass transition temperature, at 600°C for 164 h. A depth profile with secondary neutral mass spectrometry shows an enrichment of Mg at the outer 50 nm of the glass surface. The formation of films requires cation migration, which is driven by an oxygen chemical potential between air and the reduced basalt (Fe²⁺/Fe³⁺ ratio of 13.3). The change of surface alteration from Mg to Ca film at lower temperatures, to predominantly Fe at high temperatures, is determined by a change of cation availability, largely controlled by crystallization that already occurs below 850°C, and volume crystallization that occurs above 925°C.  相似文献   

Desert Potholes: Ephemeral Aquatic Microsystems   总被引：1，自引：0，他引：1  

Marjorie?A.?ChanEmail author  Katrina?Moser  Jim?M.?Davis  Gordon?Southam  Kebbi?Hughes  Tim?Graham 《Aquatic Geochemistry》2005,11(3):279-302

An enigma of the Colorado Plateau high desert is the “pothole”, which ranges from shallow ephemeral puddles to deeply carved pools. The existence of prokaryotic to eukaryotic organisms within these pools is largely controlled by the presence of collected rainwater. Multivariate statistical analysis of physical and chemical limnologic data variables measured from potholes indicates spatial and temporal variations, particularly in water depth, manganese, iron, nitrate and sulfate concentrations and salinity. Variation in water depth and salinity are likely related to the amount of time since the last precipitation, whereas the other variables may be related to redox potential. The spatial and temporal variations in water chemistry affect the distribution of organisms, which must adapt to daily and seasonal extremes of fluctuating temperature (0–60 °C), pH changes of as much as 5 units over 12 days, and desiccation. For example, many species become dormant when potholes dry, in order to endure intense heat, UV radiation, desiccation and freezing, only to flourish again upon rehydration. But the pothole organisms also have a profound impact on the potholes. Through photosynthesis and respiration, pothole organisms affect redox potential, and indirectly alter the water chemistry. Laboratory examination of dried biofilm from the potholes revealed that within 2 weeks of hydration, the surface of the desiccated, black biofilm became green from cyanobacterial growth, which supported significant growth in heterotrophic bacterial populations. This complex biofilm is persumably responsible for dissolving the cement between the sandstone grains, allowing the potholes to enlarge, and for sealing the potholes, enabling them to retain water longer than the surrounding sandstone. Despite the remarkable ability of life in potholes to persist, desert potholes may be extremely sensitive to anthropogenic effects. The unique limnology and ecology of Utah potholes holds great scientific value for understanding water–rock–biological interactions with possible applications to life on other planetary bodies.  相似文献   

The long arm of climate change: societal teleconnections and the future of climate change impacts studies   总被引：1，自引：0，他引：1  

Susanne C. Moser  Juliette A. Finzi Hart 《Climatic change》2015,129(1-2):13-26

  相似文献   

Salinity and Chlorophyll a as Performance Measures to Rehabilitate a Mangrove-Dominated Deltaic Coastal Region: the Ci��naga Grande de Santa Marta�CPajarales Lagoon Complex, Colombia     

Victor H. Rivera-Monroy  Robert R. Twilley  J. Ernesto Mancera-Pineda  Christopher J. Madden  Ariel Alcantara-Eguren  E. Barry Moser  Bror F. Jonsson  Edward Casta?eda-Moya  Oscar Casas-Monroy  Paola Reyes-Forero  Jorge Restrepo 《Estuaries and Coasts》2011,34(1):1-19

  相似文献   

Aligned olivine in the Springwater pallasite          下载免费PDF全文

Neva A. Fowler‐Gerace  Kimberly T. Tait  Desmond E. Moser  Ivan Barker  Bob Y. Tian 《Meteoritics & planetary science》2016,51(6):1125-1135

The mechanism by which olivine grains became embedded within iron‐nickel alloy in pallasite meteorites continues to be a matter of scientific debate. Geochemical and textural observations have failed to fully elucidate the origin and history of the olivine crystals; however, little research attention has been devoted to their crystallographic orientations within the metal matrix. Using electron backscatter diffraction, we have collected crystallographic orientation data for 296 crystals within ～65 cm² sample surface from Springwater. Though no global crystallographic preferred orientation exists, very low misorientations are observed among [100] axes of olivine crystals within specific texturally defined domains. Combined with a thorough characterization of large‐scale Springwater textures, the definitively nonrandom spatial distribution of olivine orientations provides clues regarding the nature of the olivine's initial formation environment as well as the sequence of events subsequent to metal incorporation.  相似文献   

U–Pb isotopic dating of titanite microstructures: potential implications for the chronology and identification of large impact structures     

K.?PapapavlouEmail authorView author&#;s OrcID profile  J.?R.?Darling  D.?E.?Moser  I.?R.?Barker  EIMF  L.?F.?White  P.?C.?Lightfoot  C.?D.?Storey  J.?Dunlop 《Contributions to Mineralogy and Petrology》2018,173(10):82

Identifying and dating large impact structures is challenging, as many of the traditional shock indicator phases can be modified by post-impact processes. Refractory accessory phases, such as zircon, while faithful recorders of shock wave passage, commonly respond with partial U–Pb age resetting during impact events. Titanite is an accessory phase with lower Pb closure temperature than many other robust chronometers, but its potential as indicator and chronometer of impact-related processes remains poorly constrained. In this study, we examined titanite grains from the Sudbury (Ontario, Canada) and Vredefort (South Africa) impact structures, combining quantitative microstructural and U–Pb dating techniques. Titanite grains from both craters host planar microstructures and microtwins that show a common twin–host disorientation relationship of 74° about <102>. In the Vredefort impact structure, the microtwins deformed internally and developed high- and low-angle grain boundaries that resulted in the growth of neoblastic crystallites. U–Pb isotopic dating of magmatic titanite grains with deformation microtwins from the Sudbury impact structure yielded a ²⁰⁷Pb/²⁰⁶Pb age of 1851?±?12 Ma that records either the shock heating or the crater modification stage of the impact event. The titanite grains from the Vredefort impact structure yielded primarily pre-impact ages recording the cooling of the ultra-high-temperature Ventersdorp event, but domains with microtwins or planar microstructures show evidence of U–Pb isotopic disturbance. Despite that the identified microtwins are not diagnostic of shock-metamorphic processes, our contribution demonstrates that titanite has great potential to inform studies of the terrestrial impact crater record.  相似文献   

Measurement of Ejecta from Normal Incident Hypervelocity Impact on Lunar Regolith Simulant     

David L. Edwards  William Cooke  Danielle E. Moser  Wesley Swift 《Earth, Moon, and Planets》2008,102(1-4):549-553

The National Aeronautics and Space Administration (NASA) continues to make progress toward long-term lunar habitation. Critical to the design of a lunar habitat is an understanding of the lunar surface environment. A subject for further definition is the lunar impact ejecta environment. The document NASA SP-8013 was developed for the Apollo program and is the latest definition of the ejecta environment. There is concern that NASA SP-8013 may over-estimate the lunar ejecta environment. NASA’s Meteoroid Environment Office (MEO) has initiated several tasks to improve the accuracy of our understanding of the lunar surface ejecta environment. This paper reports the results of experiments on projectile impact into powered pumice targets, simulating unconsolidated lunar regolith. The Ames Vertical Gun Range (AVGR) was used to accelerate spherical Pyrex projectiles of 0.29g to velocities ranging between 2.5 and 5.18 km/s. Impact on the pumice target occurred at normal incidence. The ejected particles were detected by thin aluminum foil targets placed around the pumice target in a 0.5 Torr vacuum. A simplistic technique to characterize the ejected particles was formulated. Improvements to this technique will be discussed for implementation in future tests.  相似文献