High spatial resolution analysis of ferromanganese concretions by LA-ICP-MS†     

Mikael D. Axelsson  Ilia Rodushkin  Douglas C. Baxter  Johan Ingri  Björn Öhlander 《Geochemical transactions》2002,3(1):40

A procedure was developed for the determination of element distributions in cross-sections of ferromanganese concretions using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The effects of carrier flow rates, rf forward power, ablation energy, ablation spot size, repetition rate and number of shots per point on analyte intensity were studied. It is shown that different carrier gas flow rates are required in order to obtain maximum sensitivities for different groups of elements, thus complicating the optimisation of ICP parameters. On the contrary, LA parameters have very similar effects on almost all elements studied, thus providing a common optimum parameter set for the entire mass range. However, for selected LA parameters, the use of compromise conditions was necessary in order to compensate for relatively slow data acquisition by ICP-MS and maintain high spatial resolution without sacrificing the multielemental capabilities of the technique. Possible variations in ablation efficiency were corrected for mathematically using the sum of Fe and Mn intensities. Quantification by external calibration against matrix-matched standards was successfully used for more than 50 elements. These standards, in the form of pressed pellets (no binder), were prepared in-house using ferromanganese concentrates from a deep-sea nodule reference material as well as from shallow-marine concretions varying in size and having different proportions of three major phases: aluminosilicates, Fe- and Mn-oxyhydroxides. Element concentrations in each standard were determined by means of conventional solution nebulisation ICP-MS following acid digestion. Examples of selected inter-element correlations in distribution patterns along the cross-section of a concretion are given.  相似文献   

An attempt to use LA-ICP-SMS to quantify enrichment of trace elements on pyrite surfaces in oxidizing mine tailings     

Björn Öhlander  Barbara Müller  Mikael Axelsson  Lena Alakangas 《Journal of Geochemical Exploration》2007

Metals released from oxidation and weathering of sulphide minerals in mine tailings are to a high degree retained at deeper levels within the tailings themselves. To be able to predict what could happen in the future with these secondarily retained metals, it is important to understand the retention mechanisms. In this study an attempt to use laser ablation high-resolution ICP-MS (LA-ICP-SMS) to quantify enrichment of trace elements on pyrite surfaces in mine tailings was performed. Pyrite grains were collected from a profile through the pyrite-rich tailings at the Kristineberg mine in northern Sweden. At each spot hit by the laser, the surface layer was analyzed in the first shot, and a second shot on the same spot gave the chemical composition of the pyrite immediately below. The crater diameter for a laser shot was known, and by estimating the crater depth and total pyrite surface, the total enrichment on pyrite grains was calculated. Results are presented for As, Cd, Co, Cu, Ni and Zn. The results clearly show that there was an enrichment of As, Cd, Cu and Zn on the pyrite surfaces below the oxidation front in the tailings, but not of Co and Ni. Arsenic was also enriched on the pyrite grains that survived in the oxidized zone. Copper has been enriched on pyrite surfaces in unoxidized tailings in the largest amount, followed by Zn and As. However, only 1.4 to 3.1% of the Cd and Zn released by sulphide oxidation in the oxidized zone have been enriched on the pyrite surfaces in the unoxidized tailings, but for As and Cu corresponding figures are about 64 and 43%, respectively. There were many uncertainties in these calculations, and the results shall not be taken too literally but allowed the conclusion that enrichment on pyrite surfaces is an important process for retention of As and Cu below the oxidation front in pyrite rich tailings. Laser ablation is not a surface analysis technique, but more of a thin layer method, and gives no information on the type of processes resulting in enrichment on the pyrite surfaces. Although only pyrite grains that appeared to be fresh and without surface coatings were used in this study, the possibility that a thin layer of Fe-hydroxides occurred must be considered. Both adsorption to the pyrite directly or to Fe-oxyhydroxides may explain the enrichment of As, Cd, Cu and Zn on the pyrite surfaces, and, in the case of Cu, also the replacement of Fe(II) by Cu(II) in pyrite.  相似文献   

Asteroid identification over apparitions     

Mikael Granvik  Karri Muinonen 《Icarus》2008,198(1):130-137

We present a new method for the linking of scarce asteroid astrometry over apparitions, and apply it both to simulated and real data to prove its feasibility. Up to date, there has not been a robust method available to search for linkages between the approximately 50,000 provisionally designated sets of asteroid astrometry spanning less than two days. Unless such a scarce set of astrometry is linked to another set of astrometry, the underlying object can be considered lost as the ephemeris uncertainties are substantial. The new method, which can tackle the challenges, is based on Ranging, which is a fully nonlinear, statistical orbital inversion method. Ranging properly treats astrometric uncertainties and propagates the uncertainty to the resulting orbital-element probability density, which is sampled by a set of orbits. The new orbital-element-space multiple-address-comparison (oMAC) method uses dimensionality-reduction techniques and tree structures to efficiently search for overlapping probability densities in the orbital-element phase space. Overlapping probability densities indicate a candidate linkage between astrometric observation sets. To accept a candidate linkage, we have to find a many-body orbital solution which reproduces the observed positions within the observational uncertainties. To find the linking orbit, we use a multi-step approach starting from a Monte-Carlo generation of possible orbits in a reduced volume of the orbital-element phase space and ending with a least-squares orbital solution, which, in addition to the Sun's gravitation, also takes into account the gravitational influence of the relevant planets. The new multiple-address-comparison method has a loglinear computational complexity, that is, it scales as O(nlogn), where n is the number of included observation sets. It has recently also been implemented for the ephemeris-space multiple-address-comparison (eMAC) method, which is optimized for the short-term linking of scarce astrometry.  相似文献   

The Creston,California, meteorite fall and the origin of L chondrites     

Peter Jenniskens  Jason Utas  Qing‐Zhu Yin  Robert D. Matson  Marc Fries  J. Andreas Howell  Dwayne Free  Jim Albers  Hadrien Devillepoix  Phil Bland  Aaron Miller  Robert Verish  Laurence A. J. Garvie  Michael E. Zolensky  Karen Ziegler  Matthew E. Sanborn  Kenneth L. Verosub  Douglas J. Rowland  Daniel R. Ostrowski  Kathryn Bryson  Matthias Laubenstein  Qin Zhou  Qiu‐Li Li  Xian‐Hua Li  Yu Liu  Guo‐Qiang Tang  Kees Welten  Marc W. Caffee  Matthias M. M. Meier  Amy A. Plant  Colin Maden  Henner Busemann  Mikael Granvik   《Meteoritics & planetary science》2019,54(4):699-720

It has been proposed that all L chondrites resulted from an ongoing collisional cascade of fragments that originated from the formation of the ~500 Ma old asteroid family Gefion, located near the 5:2 mean‐motion resonance with Jupiter in the middle Main Belt. If so, L chondrite pre‐atmospheric orbits should be distributed as expected for that source region. Here, we present contradictory results from the orbit and collisional history of the October 24, 2015, L6 ordinary chondrite fall at Creston, CA (here reclassified to L5/6). Creston's short 1.30 ± 0.02 AU semimajor axis orbit would imply a long dynamical evolution if it originated from the middle Main Belt. Indeed, Creston has a high cosmic ray exposure age of 40–50 Ma. However, Creston's small meteoroid size and low 4.23 ± 0.07° inclination indicate a short dynamical lifetime against collisions. This suggests, instead, that Creston originated most likely in the inner asteroid belt and was delivered via the ν₆ resonance. The U‐Pb systematics of Creston apatite reveals a Pb‐Pb age of 4,497.1 ± 3.7 Ma, and an upper intercept U‐Pb age of 4,496.7 ± 5.8 Ma (2σ), circa 70 Ma after formation of CAI, as found for other L chondrites. The K‐Ar (age ~4.3 Ga) and U,Th‐He (age ~1 Ga) chronometers were not reset at ~500 Ma, while the lower intercept U‐Pb age is poorly defined as 770 ± 320 Ma. So far, the three known L chondrites that impacted on orbits with semimajor axes a <2.0 AU all have high (>3 Ga) K‐Ar ages. This argues for a source of some of our L chondrites in the inner Main Belt. Not all L chondrites originate in a continuous population of Gefion family debris stretching across the 3:1 mean‐motion resonance.  相似文献   

Gondwana breakup: Messages from the North Natal Valley     

Maryline Moulin  Daniel Aslanian  Mikael Evain  Anglique Leprêtre  Philippe Schnurle  Fanny Verrier  Joseph Thompson  Philippe De Clarens  Sylvie Leroy  Nuno Dias 《地学学报》2020,32(3):205-214

The Natal Valley, offshore Mozambique, is a key area for understanding the evolution of East Gondwana. Within the scope of the integrated multidisciplinary PAMELA project, we present new wide‐angle seismic data and interpretations, which considerably alter Geoscience paradigms. These data reveal the presence of a 30‐km‐thick crust that we argue to be of continental nature. This falsifies all the most recent palaeo‐reconstructions of the Gondwana. This 30‐km‐thick continental crust 1,000 m below sea level implies a complex history with probable intrusions of mantle‐derived melts in the lower crust, connected to several occurrences of magmatism, which seems to evidence the crucial role of the lower continental crust in passive margin genesis.  相似文献   

Evolution of hillslope soils: The geomorphic theater and the geochemical play     

Kyungsoo Yoo  Beth Weinman  Simon Marius Mudd  Martin Hurst  Mikael Attal  Kate Maher 《Applied Geochemistry》2011

How and how fast do hillslope soils form as the landscape’s morphology changes over time? Here results are shown from an ongoing study that simultaneously examines the morphologic and geochemical evolution of soil mantled hillslopes that have been exposed to distinctively different denudation history. In Northern Sierra Nevada, California, the authors are investigating a tributary basin to the Middle Fork Feather River. A major incision signal from the river is well marked in a knickpoint within the tributary basin which stretches from its mouth to the Feather River at an elevation of ～700 m to the plateau at an elevation of ～1500 m. Hillslopes are significantly steeper below the knickpoint. The area’s total denudation rates are currently being constrained using cosmogenic radio nuclides, but a previous study suggested an order of magnitude difference in total denudation rates below and above the knickpoint. When compared with topographic attributes calculated from LIDAR data, physical erosion rates can be modeled as a linear function of ridge top curvature. Surprisingly, over the wide range of total denudation rates, soil thicknesses do not vary significantly until a threshold point where soil mantled landscapes abruptly shift to bedrock dominated landscapes. Bioturbation by tree falls appear to buffer soil thickness over the wide range of physical soil erosion rates. From three hillslopes with different physical erosion rates, the concentrations of Zr, which were considered conserved during dissolution and leaching, were determined and used as a proxy for the degree of mass losses via chemical denudation. There is a general trend that colluvial soils along the hillslopes with lower physical erosion rates are enriched in fine size fractions, Zr, and pedogenic crystalline Fe oxides. Likewise, the saprolites show greater degrees of chemical denudation at the sites above the knickpoint, presumably because of the saprolites’ longer turnover time in the slowly eroding landscapes. In the two steep hillslopes below the knickpoint, no significant or systematic topgraphic trends were found for soil geochemistry. However, soils show increasing Zr enrichment in the downslope direction in the hillslope above the knickpoint, which suggests a critical denudation rate beyond which soils’ turnover time is too short to develop a geochemical catena. As detailed CRN-based soil production rates and catchment scale denudation rates are acquired, the data will be combined with a mass balance model to calculate the rates of chemical denudation and weathering in soils and saprolites along the denudation gradient.  相似文献   

内蒙古大庙中新世哺乳动物群序列与环境变化   总被引：1，自引：0，他引：1  

张兆群  王李花  AnuKaakinen  刘丽萍  傅明楷 《第四纪研究》2011,31(4):608-613

中新世是现代地理、生态、气候格局等形成的关键时期,是研究陆生哺乳动物演化与环境变化关系的理想时段.通过对内蒙古四子王旗大庙发现的中新世哺乳动物化石的研究,试图揭示同一区域哺乳动物群落演变过程、生态类型的变化及其与环境变化的关系.结果表明大庙共产出了3个时段的动物群,分别为早中新世谢家期、中中新世通古尔期以及晚中新世灞河...  相似文献   

Theory and Experiment on an Elastically Moored Cylindrical Buoy     

Mikael Eriksson Jan Isberg Mats Leijon 《Oceanic Engineering, IEEE Journal of》2006,31(4):959-963

In this paper, we compare simulated forces and accelerations for a moored floating buoy with full-scale experimental results in real ocean waves. The buoy is moored with a wire connected by springs to a concrete foundation situated at the seafloor. This study aims to develop a computer model using potential theory with a linearized free-surface boundary condition to describe the motion of such a system. The intention is to use the model for future study of wave-energy absorption and design of converters. Another objective is to see how complex a model is required to get accurate results. The method used is computationally fast and makes it possible to couple linear buoy wave interaction with nonlinear generator models, so that different loads and latching can be studied. A computationally fast method is required to model farms of wave-energy converters  相似文献   

Laetoli,a Pliocene site in northern Tanzania. Edited by M. D. Leakey and J. M. Harris. Publisher Oxford university press,Oxford 1987 $90.00 (hardback) (xxi + 561 pp) ISBN 0 19 854441 3     

Mikael Fortelius 《第四纪科学杂志》1988,3(1):106-106

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Geochemical mapping using stream sediments in west-central Nigeria: Implications for environmental studies and mineral exploration in West Africa     

Dan J. Lapworth  Katherine V. Knights  Roger M. Key  Christopher C. Johnson  Emmanuel Ayoade  Michael A. Adekanmi  Tunde M. Arisekola  Olugbenga A. Okunlola  Birgitta Backman  Mikael Eklund  Paul A. Everett  Robert T. Lister  John Ridgway  Michael J. Watts  Simon J. Kemp  Peter E.J. Pitfield 《Applied Geochemistry》2012

This paper provides an overview of regional geochemical mapping using stream sediments from central and south-western Nigeria. A total of 1569 stream sediment samples were collected and 54 major and trace elements determined by ICP-MS and Au, Pd and Pt by fire assay. Multivariate statistical techniques (e.g., correlation analysis and principal factor analysis) were used to explore the data, following appropriate data transformation, to understand the data structure, investigate underlying processes controlling spatial geochemical variability and identify element associations. Major geochemical variations are controlled by source geology and provenance, as well as chemical weathering and winnowing processes, more subtle variations are a result of land use and contamination from anthropogenic activity.  相似文献