Physics and Chemistry of the Earth, Part A: Solid Earth and Geodesy最新文献

The role of GPS ground station data for the CHAMP Atmospheric Profiling experiment is discussed. The profiling activities at GeoForschungZentrum Potsdam (GFZ) are briefly described and first results of the occultation processing system are presented. The atmospheric excess phase of the occultation link between the CHAMP and the GPS satellite is derived by a double difference method using ground station data. The influence of ground station data on the accuracy of the derived atmospheric profiles is discussed. A relationship between the temperature errors at several heights resulting from errors in atmospheric excess phase is given, e.g. an error of 1mm/s in the time derivative of the excess phase results in a temperature error of 1 K at 30 km. Furthermore, a study was performed to estimate the required data rate of the ground station measurements. In particular the influence of the Selective Availability (SA) termination on May 2, 2000 is emphasized. We conclude that the acquisition rate can be reduced from 1 Hz to 0.1 Hz without loss of information. Simulations of the CHAMP occultation experiment show that the joint Jet Propulsion Laboratory, Pasadena (JPL) & GFZ “high rate & low latency” network enables the processing of globally distributed occultation events with a highly redundant number of ground stations. Latency aspects are studied in view of the future task of providing atmospheric occultation data for operational weather forecast.

Compaction bands are narrow planar zones of localized purely compressive (without shear) deformation that form perpendicular to the most compressive principal stress. Such bands have been observed in high porosity rocks in the laboratory and in the field. Because compaction presumably decreases permeability, these bands can act as barriers to flow within reservoirs. Reexamination of the results of Rudnicki and Rice (J. Mech. Phys. Solids, 1975) for shear localization, with corrections by Perrin and Leblond (J. Appl. Mech., 1993), reveals that they admit solutions for compaction bands in a range of parameters that is representative of porous rock. Solutions for compaction bands are possible when the inelastic volume deformation is compactive and is associated with a “cap” on the yield surface. The expression for the critical hardening modulus (related to the slope of the shear stress vs. shear strain curve at constant mean stress) at which compaction bands are predicted to form differs from that for shear localization. For parameters representative of porous rock, axisymmetric compression is the most favorable deviatoric stress state for formation of compaction bands. Comparison of conditions for shear localization and compaction band formation suggests that either may occur depending on the stress path and magnitude of the confining stress.

The early Cretaceous volcanism occurring along the Sulu orogenic belt, east Shandong Province, demonstrates a bimodal characteristic. The volcanic rocks belong to high-K alkaline series, dominated by alkali basalt, basaltic trachyandesite, latite and trachyte with LILE (e.g. K, Sr and Ba) and LREE enrichment but HFSE depletion (especially for Nb and P) in the primitive mantle-normalized spidergrams and steeply right-declined REE patterns. The enriched initial Sr-Nd isotopic ratios (⁸⁷Sr/⁸⁶Sr = 0.70724 to 0.70750 and ε_Nd(t) = −17.0 to −15.9) of the basaltic samples suggest their origin from an enriched lithospheric mantle, which might had undergone a fluid metasomatism or source mixing by the continental crust during or shortly after the Triassic continental subduction. Significantly negative Nb anomalies observed in the spidergrams and other “crustal” signatures of these rocks suggest an important role of continental material in their petrogenesis. The felsic rocks demonstrate geochemical and Sr-Nd isotopic features (initial ⁸⁷Sr/⁸⁶Sr = 0.70814 to 0.70961 and ε_Nd (t) = −18.9 to −17.0) similar to those of the post-collisional granitic plutons, probably derived from the anatexis of lower/middle crust in response to basaltic magma underplating. The widespread melting of the metasomatized mantle was probably attributed to the thermal perturbation or lithospheric extension induced by the mega-large displacement along the Tan-Lu wrench fault system when northward strike-slipping movement of the Izanagi Plate occurred during the late Mesozoic.

To deliver tropospheric water vapor contents derived from GPS ground networks for the assimilation into numerical weather prediction models the GPS data have to be analyzed within near real-time with a delay of about one hour. Two near real-time processors for the trophospheric water vapor monitoring developed at IEEC Barcelona and GFZ Potsdam are compared using one week of data acquired in the German near real-time network. The resulting small differences in the integrated water vapor being on the level of 1–2 mm precipitable water vapor reflect that both processors fulfill the requirements for numerical weather predictions. Therefore the standardization for processors should not be too strict not to obstruct a fruitful competition in the software developments and improvements.

The oxygen isotope composition of whole-rock and mineral separates was measured for granulite rocks from Dabieshan. According to their whole-rock δ¹⁸O values relative to the normal mantle δ¹⁸O values of 5.7±0.5‰, two groups are classified: (1) mafic granulite which exhibits lower δ¹⁸O values of 3.5 to 4.7‰, and (2) felsic granulite which shows higher δ¹⁸O values of 7.6 to 7.8‰. Consistent isotope temperatures of 800 to 900 °C are obtained for mineral pairs containing such refractory minerals as pyroxene, garnet, hornblende and iron oxides, suggesting the achievement and preservation of oxygen isotope equilibrium at the conditions of the peak granulite-facies metamorphism. This not only points to a rapid cooling and ascent for the granulite rocks in the early stage of exhumation, but also precludes the infiltration of external fluids during exhumation as the cause for the ¹⁸O-depletion in the mafic granulite. It is evident that the granulite rocks acquired the low δ¹⁸O values before the granulite-facies metamorphism by interaction with a certain ¹⁸O-depleted surface fluid. The surface fluid is assumed to exchange oxygen isotopes with the granulite protoliths prior to plate subduction. Fluid-absent metamorphism is suggested for the formation of the granulites on local scales. It is likely that the granulites together with the ultrahigh pressure eclogites and gneisses in Dabieshan were part of a single tectonic entity in the processes of subduction and Triassic metamorphism but experienced differential two-stage uplifts prior to amphibolite-facies retrogression.

To estimate total absolute tropospheric zenith delays in a global network of GPS stations, residual delays are estimated as corrections to an a priori delay model using a zenith angle dependent mapping function. Because the a priori model relies on a standard atmosphere and the wet and hydrostatic delays have different zenith angle dependence, the total zenith delay estimates are biased. A simulation has shown that biases of several mm are possible, especially when a crude mapping function, large zenith cut-off angles and no zenith angle dependent weighting is used.

Peat contains mostly diamagnetic organic matter, which is a good collector of all kinds of atmospheric dusts and industrial pollution. Ombrotrophic peat bogs are built up above the ground water table, so deposition and accumulation of magnetic particles are not influenced by ground water and the deposited particles remain largely “in situ”. During this study, 6 Polish ombrotrophic peat bogs from different locations have been investigated. Peat cores of about 30–50 cm in depth were taken from every bog. The specific low-frequency magnetic susceptibility was measured along the peat profile in fresh, not dried sample. In most profiles the susceptibility below 10 cm was slightly negative, which is characteristic for clean organic material. Above a depth 8–10 cm the susceptibility starts to increase. Independently of the profile location, the increase is observed in all bogs and according to isotopic (C-14) dating it is connected with the post war industrialisation (1945–1955). The maximum of the magnetic deposition noticed as maximum susceptibility enhancement is observed in a depth of about 5 cm below the surface. In the south-western part of Poland the peat profiles show the maximum susceptibility above 350 ×10⁻⁸m³kg⁻¹. The susceptibility decreases in profiles from the central part of Poland to 30–60. In the northern and southeastern part of the country the maximum observed susceptibility is about 10 ×10⁻⁸m³kg⁻¹. Hysteresis parameters pointed at anthropogenic ferromagnetic minerals as a carrier of magnetic signal.