Trace element variations in olivine phenocrysts from Ugandan potassic rocks as clues to the chemical characteristics of parental magmas   总被引：2，自引：0，他引：2  

Stephen F. Foley  Dorrit E. Jacob  Hugh St. C. O’Neill 《Contributions to Mineralogy and Petrology》2011,162(1):1-20

Olivine phenocrysts in ugandite and leucite basanite from the western branch of the East African Rift have been analysed for up to 34 trace elements by Laser-ICP-MS with detection limits as low as 1 ppb. A combination of point analyses with varying ablation crater diameters and line scans allow the identification of subtle zonations from core to rim, as well as characterization of the chemical effects of contamination along cracks. Trace element concentrations are remarkably uniform between large and small phenocrysts; fractionated leucite basanites (Mg# 59) have higher D _Ca and D _Al, and less fractionated LREE/HREE than MgO-rich ugandites (Mg# 75–80). Minor zonation is seen in elements with cation charges from 5+ to 2+ (P, Ti, Zr, Cr, Al, Sc, V, Cu, Mn, Ni) and show correlation between Ti and Al, but not P. Early phenocryst cores with high Li or Ni, low Mn, or enrichments in many trace elements can be identified, whereas xenocrysts have exceptionally low Na, Cr, Ti, V and Co. Partition coefficients for Ni are 31–35, less than in lamproites, with which they demonstrate an approximately linear correlation with K₂O content, K₂O/Al₂O₃ and K₂O/Na₂O of the melt, but none with SiO₂ content or Mg#. D-values for Cr, Mn and Co overlap with those of basalts, whereas those for Sc (0.011–0.018), Zn (0.44–0.49) and Ga (0.006–0.007) are lower. D _V of various potassic rocks (0.015 in the Ugandan rocks) confirms the dependence on fO₂ calibrated by the Fe³⁺/(Fe³⁺+Fe²⁺) of spinels; the Ugandan potassic rocks crystallized at fO₂ = FMQ to FMQ + 1. The ugandite olivines have some trace element characteristics reminiscent of those in metasomatized Kaapvaal peridotites, but not ocean islands. Line scan analyses are contaminated in Al, Ca, Cu, Ga, Sr, Zr, Nb, La and Ce, elements that are also concentrated in microcracks between subgrains, indicating smearing out during polishing, and demonstrating that large spot analyses produce the best results.  相似文献   

Determination of Reference Values for NIST SRM 610–617 Glasses Following ISO Guidelines     

Klaus Peter Jochum  Ulrike Weis  Brigitte Stoll  Dmitry Kuzmin  Qichao Yang  Ingrid Raczek  Dorrit E. Jacob  Andreas Stracke  Karin Birbaum  Daniel A. Frick  Detlef Günther  Jacinta Enzweiler 《Geostandards and Geoanalytical Research》2011,35(4):397-429

We present new reference values for the NIST SRM 610–617 glasses following ISO guidelines and the International Association of Geoanalysts’ protocol. Uncertainties at the 95% confidence level (CL) have been determined for bulk‐ and micro‐analytical purposes. In contrast to former compilation procedures, this approach delivers data that consider present‐day requirements of data quality. New analytical data and the nearly complete data set of the GeoReM database were used for this study. Data quality was checked by the application of the Horwitz function and by a careful investigation of analytical procedures. We have determined quantitatively possible element inhomogeneities using different test portion masses of 1, 0.1 and 0.02 μg. Although avoiding the rim region of the glass wafers, we found moderate inhomogeneities of several chalcophile/siderophile elements and gross inhomogeneities of Ni, Se, Pd and Pt at small test portion masses. The extent of inhomogeneity was included in the determination of uncertainties. While the new reference values agree with the NIST certified values with the one exception of Mn in SRM 610, they typically differ by as much as 10% from the Pearce et al. (1997) values in current use. In a few cases (P, S, Cl, Ta, Re) the discrepancies are even higher.  相似文献   

Long-term Changes and Controlling Factors of Phytoplankton Community in the Gulf of Riga (Baltic Sea)     

Iveta Jurgensone  Jacob Carstensen  Anda Ikauniece  Baiba Kalveka 《Estuaries and Coasts》2011,34(6):1205-1219

Trends in phytoplankton monitoring data (1976–2008) from the Gulf of Riga were investigated and linked to environmental factors. Annual means of spring phytoplankton biomass correlated to phosphorus input from land and shifts between diatoms and dinoflagellates were attributed to potential Si limitation and time of sampling relative to the spring phytoplankton succession. The summer phytoplankton biomass, which more than doubled over the study period, was related to the abundance of summer copepods that similarly declined. Cyanobacterial blooms proliferated in summer and the proportion of diatoms similarly declined when the winter–spring inorganic N/P ratio was low. The chlorophyte proportion in summer increased over the study period, and this was linked to increasing temperatures favoring their higher growth rates. The dinoflagellate proportion appeared to decrease with temperatures above a threshold of 15.5°C. Although nutrient inputs and their ratios are important factors for the phytoplankton community, this study suggests that climate change and overfishing could be equally important.  相似文献   

The MESSENGER mission to Mercury: scientific objectives and implementation     

Sean C. Solomon  Ralph L. McNutt  Jr.  Robert E. Gold  Mario H. Acua  Daniel N. Baker  William V. Boynton  Clark R. Chapman  Andrew F. Cheng  George Gloeckler  James W. Head III  Stamatios M. Krimigis  William E. McClintock  Scott L. Murchie  Stanton J. Peale  Roger J. Phillips  Mark S. Robinson  James A. Slavin  David E. Smith  Robert G. Strom  Jacob I. Trombka  Maria T. Zuber 《Planetary and Space Science》2001,49(14-15)

Mercury holds answers to several critical questions regarding the formation and evolution of the terrestrial planets. These questions include the origin of Mercury's anomalously high ratio of metal to silicate and its implications for planetary accretion processes, the nature of Mercury's geological evolution and interior cooling history, the mechanism of global magnetic field generation, the state of Mercury's core, and the processes controlling volatile species in Mercury's polar deposits, exosphere, and magnetosphere. The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission has been designed to fly by and orbit Mercury to address all of these key questions. After launch by a Delta 2925H-9.5, two flybys of Venus, and two flybys of Mercury, orbit insertion is accomplished at the third Mercury encounter. The instrument payload includes a dual imaging system for wide and narrow fields-of-view, monochrome and color imaging, and stereo; X-ray and combined gamma-ray and neutron spectrometers for surface chemical mapping; a magnetometer; a laser altimeter; a combined ultraviolet–visible and visible-near-infrared spectrometer to survey both exospheric species and surface mineralogy; and an energetic particle and plasma spectrometer to sample charged species in the magnetosphere. During the flybys of Mercury, regions unexplored by Mariner 10 will be seen for the first time, and new data will be gathered on Mercury's exosphere, magnetosphere, and surface composition. During the orbital phase of the mission, one Earth year in duration, MESSENGER will complete global mapping and the detailed characterization of the exosphere, magnetosphere, surface, and interior.  相似文献   

Multisite campaign on the open cluster M67 – I. Observations and photometric reductions     

D. Stello  T. Arentoft  T. R. Bedding  M. Y. Bouzid  H. Bruntt  Z. Csubry  T. H. Dall  Z. E. Dind  S. Frandsen  R. L. Gilliland  A. P. Jacob  H. R. Jensen  Y. B. Kang  S.-L. Kim  L. L. Kiss  H. Kjeldsen  J.-R. Koo  J.-A. Lee  C.-U. Lee  J. Nuspl  C. Sterken  R. Szabó 《Monthly notices of the Royal Astronomical Society》2006,373(3):1141-1150

We report on an ambitious multisite campaign aimed at detecting stellar variability, particularly solar-like oscillations, in the red giant stars in the open cluster M67 (NGC 2682). During the six-week observing run, which comprised 164 telescope nights, we used nine 0.6-m to 2.1-m class telescopes located around the world to obtain uninterrupted time series photometry. We outline here the data acquisition and reduction, with emphasis on the optimization of the signal-to-noise ratio of the low-amplitude (50–500 μmag) solar-like oscillations. This includes a new and efficient method for obtaining the linearity profile of the CCD response at ultrahigh precision (∼10 parts per million). The noise in the final time series is 0.50 mmag per minute integration for the best site, while the noise in the Fourier spectrum of all sites combined is 20 μmag. In addition to the red giant stars, this data set proves to be very valuable for studying high-amplitude variable stars such as eclipsing binaries, W UMa systems and δ Scuti stars.  相似文献   

Improving Groundwater Model Calibration with Repeat Microgravity Measurements     

Jeffrey R. Kennedy  Libby Wildermuth  Jacob E. Knight  Joshua Larsen 《Ground water》2022,60(3):393-403

Groundwater-flow models depend on hydraulic head and flux observations for evaluation and calibration. A different type of observation—change in storage measured using repeat microgravity—can also be used for parameter estimation by simulating the expected change in gravity from a groundwater model and including the observation misfit in the objective function. The method is demonstrated using new software linked to MODFLOW input and output files and field data from the vicinity of the All American Canal in southeast California, USA. Over a 10-year period following lining of the previously highly permeable canal with concrete, gravity decreased by over 100 μGal (equivalent to about 2.5 m of free-standing water) at some locations as seepage decreased and the remnant groundwater mound dissipated into the aquifer or was removed by groundwater pumping. Simulated gravity from a MODFLOW model closely matched observations, and repeat microgravity data proved useful for constraining both hydraulic conductivity and specific yield estimates. Specific yield estimated using the infinite-horizontal slab approximation agreed well with model-derived values, and the departure from the linear, flat-water-table approximation was small, less than 2%, despite relatively large and dynamic water-table slope. First-order second-moment parameter uncertainty analysis shows reduction in uncertainty for all hydraulic conductivity and specific yield parameter estimates with the addition of repeat microgravity data, as compared to drawdown data alone.  相似文献   

Towards household food security in Ghana: assessment of Ghana’s expanded forest plantation programme in Asante Akim South District     

Jacob Obodai  Prince Osei-Wusu Adjei  Simon Victory Quarcson Hamenoo  Abena Korang Acheampong Abaitey 《GeoJournal》2018,83(2):365-380

This study primarily presents a contribution analysis of the outcomes of the expanded forest plantation programme (EFPP) as a community-based forest governance intervention to enhance household food security. A cross sectional research design with simple random sampling technique was used to select the study sites and respondents. In all, four (4) out of ten (10) settlements implementing the EFPP in the Asante Akyim South District of Ghana were selected. Questionnaires were administered to 80 beneficiaries proportionally selected from the study sites and in-depth interviews were conducted with key stakeholders implementing the programme. The discussion of the results was informed by the theory of change analysis framework to assess the contribution of the programme to household food security. The theory of change tool helped to identify progress towards the achievement of potential and probable outcomes of the programme. The findings reveal that the availability of food crops at the household level and the district at large increased through the EFPP. Between the years 2011 and 2013, 2763.1426 Metric Tonnes (Mt) of food crops were produced from 444.4046 ha of land in the district from the programme. Also, an average of GH¢ 229 ($72) comprising both monthly allowances received for planting and nurturing trees and income derived from the sale of food crops produced increased the economic power and livelihood outcomes of beneficiaries. This has had a contributing effect on the physical availability and accessibility of food crops at the household level. Hence, scaling up the EFPP to cover many beneficiaries, and a budget allocation for the food crop production component of the programme through the provision of improved crop seeds for interplanting would promote food production and security at the household and district levels.  相似文献   

Experimental and Numerical Studies of Velocity and Turbulence Intensities for Mid-Channel Bar     

Khan  Md. Amir  Sharma  Nayan  Odgaard  Jacob 《Water Resources》2021,48(5):746-762

Water Resources - Turbulent phenomenon in braided rivers is much more complex compared to the straight and meandering rivers. The turbulent flow structure at locations upstream and downstream of...  相似文献   

Experimental investigation of the morphodynamic response of riffles and pools to unsteady flow and increased sediment supply     

Jacob A. Morgan  Peter A. Nelson 《地球表面变化过程与地形》2021,46(4):869-886

Gravel-bed rivers characteristically exhibit shallow riffles in wide sections and deeper pools where the channel becomes constricted and narrow. While rivers can adjust to changing flow and sediment supply through some combination of adjustments of channel slope, bed-surface sorting, and channel shape, the degree to which riffle-pools may adopt these changes in response to changing flows and sediment supplies remains unclear. This article presents results from a flume experiment investigating how constant- and variable-width channels adjust their morphology in response to changing flow and increased sediment supply. Two flume geometries were used: (1) constant-width and (2) variable-width, characterized by a sinusoidal pattern with a mean width equal to that of the first channel. The variable-width channel developed bed undulations in phase with the width, representing riffle-pools. The experiment consisted of three phases for each flume geometry: (1) steady flow, constant sediment supply; (2) unsteady flow, constant sediment supply; and (3) unsteady flow, doubled sediment supply. Unsteady flow was implemented in the form of repeated symmetrical stepped hydrographs, with a mean discharge equal to that in the steady flow phase. In all phases the bed and sediment supply were composed of a sand/gravel mixture ranging from 1 to 8 mm. In both the straight and variable-width channels, transitioning from steady flow to repeated hydrographs did not result in significant changes in bed morphology. The two channel geometries had different responses to increased sediment supply: the slope of the straight channel increased nearly 40%, while the variable-width channel reduced the relief between bars and pools and decreased the variability in cross-sectional elevation with a slight slope increase. Bar-pool relief varied with repeat discharge hydrographs. Pool elevation changed twice the distance of bar elevations, emphasizing the relevance of pool scour for riffle-pool self-maintenance in channels with width variations.  相似文献   

Factors that contribute to the elongation of drumlins beneath the Green Bay Lobe,Laurentide Ice Sheet     

Lucas K. Zoet  J. Elmo Rawling III  Jacob B. Woodard  Nolan Barrette  David M. Mickelson 《地球表面变化过程与地形》2021,46(13):2540-2550

Drumlin shape has been hypothesized to correlate with ice-flow duration and slip speed, but modern-day analogues and the Coulomb nature of till render the basis of these correlations in question. The evolution of flow-parallel subglacial landforms is of importance for ice flow because the form drag they provide may be a dominant factor in regulating glacier slip speeds. Here we examine the relationship between drumlin shape and cumulative slip displacement (i.e. time-integrated slip speed) as a dominant glaciological control on drumlin shape. First, a new method is developed that allows slip speed to be estimated for deformable bedded glaciers along a flow line from an ice surface profile. Then, reconstructed surface profiles for ice margin chronologies of the Green Bay Lobe (GBL) are used to construct and estimate the spatially varying cumulative slip displacement for use in comparison with drumlin elongation ratios. We focus on a sector of the GBL near the central flow line where the geology is simple and glaciological controls are likely to dominate bedform development. Using Bayesian statistical analysis, a positive and statistically robust relationship between cumulative slip displacement and drumlin elongation ratio is found. Our analysis indicates that drumlin shape could be used to infer palaeo glacier slip speeds if time under the ice can be well constrained and geologic influences are minimal. These findings also suggest that drumlin-supplied drag could decrease with increased cumulative slip displacement in the absence of rigid geologic features that fix drumlin positions.  相似文献