Combined Earth orientation parameters based on homogeneous and continuous VLBI and GPS data   总被引：1，自引：3，他引：1  

Daniela Thaller  Manuela Krügel  Markus Rothacher  Volker Tesmer  Ralf Schmid  Detlef Angermann 《Journal of Geodesy》2007,81(6-8):529-541

The CONT02 campaign is of great interest for studies combining very long baseline interferometry (VLBI) with other space-geodetic techniques, because of the continuously available VLBI observations over 2 weeks in October 2002 from a homogeneous network. Especially, the combination with the Global Positioning System (GPS) offers a broad spectrum of common parameters. We combined station coordinates, Earth orientation parameters (EOPs) and troposphere parameters consistently in one solution using technique- specific datum-free normal equation systems. In this paper, we focus on the analyses concerning the EOPs, whereas the comparison and combination of the troposphere parameters and station coordinates are covered in a companion paper in Journal of Geodesy. In order to demonstrate the potential of the VLBI and GPS space-geodetic techniques, we chose a sub-daily resolution for polar motion (PM) and universal time (UT). A consequence of this solution set-up is the presence of a one-to-one correlation between the nutation angles and a retrograde diurnal signal in PM. The Bernese GPS Software used for the combination provides a constraining approach to handle this singularity. Simulation studies involving both nutation offsets and rates helped to get a deeper understanding of this singularity. With a rigorous combination of UT1–UTC and length of day (LOD) from VLBI and GPS, we showed that such a combination works very well and does not suffer from the systematic effects present in the GPS-derived LOD values. By means of wavelet analyses and the formal errors of the estimates, we explain this important result. The same holds for the combination of nutation offsets and rates. The local geodetic ties between GPS and VLBI antennas play an essential role within the inter-technique combination. Several studies already revealed non-negligible discrepancies between the terrestrial measurements and the space-geodetic solutions. We demonstrate to what extent these discrepancies propagate into the combined EOP solution.  相似文献   

Chemical Characterisation of the USGS Reference Glasses GSA-1G, GSC-1G, GSD-1G, GSE-1G, BCR-2G, BHVO-2G and BIR-1G Using EPMA, ID-TIMS, ID-ICP-MS and LA-ICP-MS   总被引：6，自引：2，他引：6  

Klaus Peter Jochum  Matthias Willbold  Ingrid Raczek  Brigitte Stoll  Kirstin Herwig 《Geostandards and Geoanalytical Research》2005,29(3):285-302

The USGS reference glasses GSA-1G, GSC-1G, GSD-1G, GSE-1G, BCR-2G, BHVO-2G and BIR-1G were investigated by different analytical techniques. All these materials have a geological (basaltic) matrix and are therefore useful in igneous geochemistry as matrix-matched reference materials for microanalytical techniques. The new GS glasses have trace elements in groups at concentration levels of about < 0.01, 5, 50 and 500 μg g^-1. Their major element compositions have been determined by EPMA, and trace elements have been analysed by LA-ICP-MS and two isotope dilution techniques using TIMS and ICP-MS. EPMA and LA-ICP-MS analyses indicated that the USGS reference glasses are homogeneous at the μm to mm scale with respect to major (variations < 1-2%) and most trace elements (variations 1-4%). Trace element data obtained from the different analytical techniques agreed within an uncertainty of 1-5%, indicating that between method results are comparable. Therefore, the preliminary working values for the four USGS GS glasses calculated from these data have a low level of uncertainty.  相似文献   

Volcanic stratigraphy of large-volume silicic pyroclastic eruptions during Oligocene Afro-Arabian flood volcanism in Yemen   总被引：1，自引：0，他引：1  

Ingrid Ukstins Peate  Joel A. Baker  Mohamed Al-Kadasi  Abdulkarim Al-Subbary  Kim B. Knight  Peter Riisager  Matthew F. Thirlwall  David W. Peate  Paul R. Renne  Martin A. Menzies 《Bulletin of Volcanology》2005,68(2):135-156

A new stratigraphy for bimodal Oligocene flood volcanism that forms the volcanic plateau of northern Yemen is presented based on detailed field observations, petrography and geochemical correlations. The >1 km thick volcanic pile is divided into three phases of volcanism: a main basaltic stage (31 to 29.7 Ma), a main silicic stage (29.7 to 29.5 Ma), and a stage of upper bimodal volcanism (29.5 to 27.7 Ma). Eight large-volume silicic pyroclastic eruptive units are traceable throughout northern Yemen, and some units can be correlated with silicic eruptive units in the Ethiopian Traps and to tephra layers in the Indian Ocean. The silicic units comprise pyroclastic density current and fall deposits and a caldera-collapse breccia, and they display textures that unequivocally identify them as primary pyroclastic deposits: basal vitrophyres, eutaxitic fabrics, glass shards, vitroclastic ash matrices and accretionary lapilli. Individual pyroclastic eruptions have preserved on-land volumes of up to ∼850 km³. The largest units have associated co-ignimbrite plume ash fall deposits with dispersal areas >1×10⁷ km² and estimated maximum total volumes of up to 5,000 km³, which provide accurate and precisely dated marker horizons that can be used to link litho-, bio- and magnetostratigraphy studies. There is a marked change in eruption style of silicic units with time, from initial large-volume explosive pyroclastic eruptions producing ignimbrites and near-globally distributed tuffs, to smaller volume (<50 km³) mixed effusive-explosive eruptions emplacing silicic lavas intercalated with tuffs and ignimbrites. Although eruption volumes decrease by an order of magnitude from the first stage to the last, eruption intervals within each phase remain broadly similar. These changes may reflect the initiation of continental rifting and the transition from pre-break-up thick, stable crust supporting large-volume magma chambers, to syn-rift actively thinning crust hosting small-volume magma chambers.Electronic Supplementary Material Supplementary material is available for this article at  相似文献   

Spectral features of large type IV bursts and interrelation to solar-terrestrial phenomena     

S. T. Akinyan  E. I. Mogilevsky  A. Böhme  A. Krüger 《Solar physics》1971,20(1):112-121

The type IV burst phenomenon consists of at least five physically distinct components or phases. Concerning the spectral and polarization characteristics of the radio emission, the X-ray emission and the association of energetic particle emission, two main classes of type IV burst components can be distinguished. The first class associated with energetic particle events comprises the (especially hard) X-ray burst, the type IV and mA₁ components. With respect to the dynamics of the burst source a quasistationary mA₁-phase can be distinguished from a moving mA₂-phase. The general tendencies of the development of large type IV events have been discussed with regard to the possibility of the occurrence of neutral points of the magnetic field in greater coronal heights.  相似文献   

Tectonic significance of deformation patterns in granitoid rocks of the Menderes nappes, Anatolide belt, southwest Turkey     

Klaus Gessner  Sandra Piazolo  Talip Güngör  Uwe Ring  Alfred Kröner  Cees W. Passchier 《International Journal of Earth Sciences》2001,89(4):766-780

Deformation fabrics in Proterozoic/Cambrian granitic rocks of the Çine nappe, and mid-Triassic granites of the Bozdag nappe constrain aspects of the tectonometamorphic evolution of the Menderes nappes of southwest Turkey. Based on intrusive contacts and structural criteria, the Proterozoic/Cambrian granitic rocks of the Çine nappe are subdivided into older orthogneisses and younger metagranites. The deformation history of the granitic rocks documents two major deformation events. An early, pre-Alpine deformation event (D_PA) during amphibolite-facies metamorphism affected only the orthogneisses and produced predominantly top-to-NE shear-sense indicators associated with a NE-trending stretching lineation. The younger metagranites are deformed both by isolated shear zones, and by a major shear zone along the southern boundary of the Çine submassif. We refer to this Alpine deformation event as D_A3. D_A3 shear zones are associated with a N-trending stretching lineation, which formed during greenschist-facies metamorphism. Kinematic indicators associated with this stretching lineation reveal a top-to-south sense of shear. The greenschist-facies shear zones cut the amphibolite-facies structures in the orthogneisses. ²⁰⁷Pb/²⁰⁶Pb dating of magmatic zircons from a metagranite, which crosscuts orthogneiss containing amphibolite-facies top-to-NE shear-sense indicators, shows that D_PA occurred before 547.2ǃ.0 Ma. Such an age is corroborated by the observation that mid-Triassic granites of the Çine and Bozdag nappes lack D_PA structures. The younger, top-to-south fabrics formed most likely as a result of top-to-south Alpine nappe stacking during the collision of the Sakarya continent with Anatolia in the Eocene.  相似文献   

A method for estimating vegetation change over time and space     

LI Maihe  Norbert Kr?uchi 《地理学报》2003,13(4):447-454

Plant diversity is used as an indicator of the well-being of vegetation and ecological systems. Human activities and global change drive vegetation change in composition and competition of species through plant invasions and replacement of existing species on a given scale. However, species diversity indices do not consider the effects of invasions on the diversity value and on the functions of ecosystems. On the other hand, the existing methods for diversity index can not be used directly for cross-scale evaluation of vegetation data. Therefore, we proposed a 3-dimensional model derived from the logistic equation for estimating vegetation change, using native and non-native plant diversity. The two variables, based on the current and the theoretical maximum diversity of native plants on a given scale, and the result of the model are relative values without units, and are therefore scale-independent. Hence, this method developed can be used directly for cross-scale evaluations of vegetation data, and indirectly for estimating ecosystem or environmental change.  相似文献   

Propagation pathways and fluid transport of hydrofractures in jointed and layered rocks in geothermal fields     

Agust Gudmundsson  Ingrid Fjeldskaar  Sonja L. Brenner 《Journal of Volcanology and Geothermal Research》2002,116(3-4)

Palaeofluid-transporting systems, observed as networks of mineral-filled veins in deeply eroded parts of extinct geothermal fields, indicate that hydrofractures commonly supply fluids to geothermal fields. Here we examine well-exposed vein networks that occur at crustal depths of around 1.5 km below the initial surface of the Tertiary lava pile in North Iceland. The veins are located in the damage zone of a major fault zone that dissects basaltic lava flows, the most common host rocks of geothermal fields in Iceland. The lava flows contain numerous weaknesses, particularly columnar (cooling) joints and contacts. For hydrofractures to supply fluids to geothermal fields, the fractures must be able to propagate, and transport fluids, to the surface. We explore hydrofracture pathway formation using boundary-element models of hydrofractures with fluid overpressure varying linearly from 10 MPa at the fracture centre to 0 MPa at the fracture tip (or the fluid front). The hydrofractures propagate through a vertically jointed and horizontally layered pile of lava flows with a general rock-matrix Young’s modulus of 1×10¹⁰ Pa and a Poisson’s ratio of 0.25. The joints and contacts between layers are modelled as internal springs, each with a stiffness (‘strength’) of 6 MPa/m. The location and sizes of discontinuities, as well as the location of the hydrofracture tip, vary between the models. The results indicate that tensile stresses generated at the tip of an overpressured hydrofracture can open up horizontal and vertical discontinuities out to a considerable distance from the tip, and that these discontinuities eventually link up to form the hydrofracture pathway. Analytical models indicate that for a hot spring of a given yield associated with a fault, the dimensions of the fluid-transporting part of the fault are likely to be similar for a typical normal fault and a strike-slip fault. Also, a hot spring of yield 180 l/s (the maximum in the low-temperature fields of Iceland) can be supplied through a hydrofracture of aperture 3 mm and trace length 1.2 m. These dimensions are very similar to those of typical veins in the studied networks. Buoyancy, rather than excess pressure in the fluid source, appears to be the primary driving force of hydrofractures in the geothermal fields of Iceland.  相似文献   

Permeabilities and Chemical Properties of Water in Crystalline Rocks of the Black Forest, Germany     

Ingrid Stober 《Aquatic Geochemistry》1997,3(1):43-60

Investigations were carried out to determine the hydraulic and hydrochemical properties of crystalline rocks in the Black Forest of Germany and neighbouring regions. Rock permeabilities (K) were determined to a depth of 3500 m. These parameters range from K = 3.5 × 10-10 ms-1 to K = 8.7 × 10-5 ms-1; and can increase up to an order of magnitude which is typical for porous aquifers. It is shown that on an average, granites are more pervious than gneisses and only the permeabilities of gneisses decrease with depth. The geochemistry of natural waters in crystalline rocks is not constant, but varies with depth and location. The concentration increases with depth and the water-type changes from a Ca–-Na–-HCO 3-type (or Na–-Ca–-HCO3–-) at shallow depths to a Na–-Cl-type at greater depths. Thermal springs are found only in granitic rocks with on average higher permeabilities than in gneisses. Thermal waters are welling up in valleys at the bottom of steep mountains. The chemical composition of thermal spring water is identical to that of water found at greater depths. Using geothermometers it is found, that the depth of the deposits of thermal spring water in the crystalline basement rocks of the Black Forest is some 1000 m below the surface. The topographic relief in the mountains induces a deep circulation of infiltrating rain-water with an upwelling as thermal springs in the valleys.  相似文献   

Effect of N content and soil texture on the decomposition of organic matter in forest soils as revealed by solid-state CPMAS NMR spectroscopy     

Marie-France Dignac  Heike Knicker  Ingrid Kgel-Knabner 《Organic Geochemistry》2002,33(12):157

N has a controlling effect on litter biodegradation in the forest floor, while stabilization of organic matter in the mineral soil may be influenced by physical parameters related to soil texture. In this study, in order to understand the processes involved in soil organic matter (SOM) formation, the chemical composition of SOM was followed and evaluated with regards to N contents and soil texture. Samples were taken on sites covered with Norway spruce and displaying contrasting values of C/N ratios in the forest floor. The chemical structure of OM was characterized using solid-state CPMAS ¹³C and ¹⁵N nuclear magnetic resonance (NMR) spectroscopy, along with Proton Spin Relaxation Editing (PSRE) sequences. Four groups of sampling sites were defined based on the NMR spectra of Oh and A horizons. In each group displaying similar NMR characteristics, N content and soil texture could be highly different among sites. Some Oh horizons with similar NMR spectra had very different N contents. Highly humified OM in Oh horizons were observed mainly on sites with low N contents. Some A horizons with different soil texture displayed similar OM chemical structure. High contents of O-alkyl C in some A horizons could originate from higher fresh root material input.  相似文献   

Refractory organic carbon in particle-size fractions of arable soils II: organic carbon in relation to mineral surface area and iron oxides in fractions <6 μm     

Rita Kiem  Ingrid Kgel-Knabner 《Organic Geochemistry》2002,33(12):434

The interaction of organic compounds with the mineral phase is considered as one stabilization mechanism for organic carbon (OC) in soils. The objective of this study is to assess the role of mineral surfaces for the long-term stabilization of OC in arable soils, with special emphasis on iron oxides. Soil samples were taken from two contrasting treatment types, i.e. fertilized plots and C-depleted plots, in long-term agroecosystem experiments. The soil organic carbon pool of the C-depleted plots is considered to show a lower contribution of labile compounds and consequently to be relatively enriched in refractory compounds compared with the fertilized counterparts. In fractions <6 μm, OC was studied in relation to total mineral surface area, surface area contributed by oxides and silicates, and the content and type of iron oxides (dithionite and oxalate extractable iron, Fe_d and Fe_o). In two sandy soils, OC contents were linearly related to total mineral surface area and the content of the two iron oxide fractions (Fe_d and Fe_o). The surface area developed by the silicates was low and thus the surface area contribution from oxides was dominant in fractions <6 μm. In contrast to the sandy soils, in a loamy soil OC was not correlated with surface area or the iron oxide content. However, the different soils agreed with respect to the behavior of C in density fractions: losses of OC occurred mainly from the light fraction (2 g cm⁻³), whereas C in the heavy fraction (>2 g cm⁻³) proved to be stable. For the sandy soils, mineral surface area appears to control the storage of OC in fine fractions. Given the dominant surface area contribution from oxides, OC storage here primarily depends on the oxides. The C-depleted plots in particular show that surface area controls the accumulation of refractory C. The interaction of organic compounds with the mineral phase, mainly with the surface of oxides, seems to be a major mechanism for the long-term stabilization of OC in these sandy soils. An interaction with minerals seems to be important for stabilizing OC also in the loamy soil, although this is not reflected by a proportional relation between OC and surface area across the fractions.  相似文献