Decomposition of fayalite (Fe2SiO4) in an oxygen potential gradient at 1,418 K

The decomposition of fayalite (Fe₂SiO₄) in oxygen potential gradients is studied at T=1,418 K. The compound will be decomposed into its component oxides wüstite, Fe_1?δO, and silica, SiO₂, by the simultaneous action of two different oxygen partial pressures, exceeding a critical ratio, despite the fact that fayalite is stable at both the lower and the higher oxygen potential. A quantitative analysis of the decomposition process caused by defect fluxes within the bulk Fe₂SiO₄ is given.     

The western desert — an example for geodetic problems in arid areas

In this paper some methodical aspects concerning the construction of an accurate geodetic network in arid areas and the connection of the new points to an existing network are discussed. In this context special attention is rapid on the determination of the station heights above the geoid. For the Western Desert in Egypt, which can be regarded as an example of an arid, geodetically underdeveloped region, an observational program is outlined that combines Doppler-measurements with an astrogravimetric-levelling.     

Li,Pb and Tl abundances in the K-alkaline rocks from the Middle Latina Valley volcanoes (southern Latium,Italy) and their petrological significance

Li, Pb and Tl contents of 15 primitive lava samples from the Middle Latina Valley volcanoes (southern Latium, Italy) are higher in the high-K than in the K-Series rocks, the enrichment factors roughly following the increase of the ionic size of the elements.The abundances in both series are higher than those of typical alkali basalts from oceanic environments, but similar to those of granitoid rocks. Such anomalous features may be explained as due to either crustal contamination of the parental magmas or derivation of these latter from a lithophile-enriched mantle region due to metasomatism by a lower crust-derived fluid. In both hypotheses, however, a larger involvement of crustal materials is suggested for the HKS rocks.Comparison of Li, Pb and Tl abundances in the primitive rocks of the Middle Latina Valley and Roccamonfina volcanoes shows that, unlike the KS rocks from the two districts show comparable levels and probably originated under similar conditions, the HKS rocks from the Middle Latina Valley are enriched in Li, Pb and Tl relative to their analogues from Roccamonfina. This suggests either a higher involvement of crustal materials in their genesis, or an evolution at shallower depth in the crust.     

Subophitic lithologies in KREEP-rich poikilitic impact melt rocks from Cayley Plains,Apollo 16 — remnants of a volcanic highland crust?

KREEP-rich poikilitic impact melt rocks 65777,11, 65015,88, and 62235,66 are the only mafic impact melt rocks from Cayley Plains stations, Apollo 16, from which areas of subophitic texture can be reported.The bulk chemistry of these unique subophitic areas and the surrounding poikilitic matrices, as well as mineral compositions (olivine, plagioclase, pyroxene, Fe-Ni metal) were determined by electron microprobe analysis. All subophitic areas could be undoubtedly identified as impact melt rockclasts. Inclusion 65777,11 II is of uniquely KREEP-rich composition, 62235,66 II can be classified as anorthositic. Therefore our attempt to identify pristine volcanic basement rocks of the Cayley regions among these inclusions of basaltic texture failed.However, the absence of pristine volcanic target rock fragments and the existence of KREEP-rich and anorthositic impact melt clasts in KREEP-rich impact melt rocks from Cayley Plains favors the theory that the Cayley Plains formation is part of the ejecta blanket from a large basin-type impact crater (Imbrium?), which is underlain by anorthositic material (Nectaris ejecta?), and has been reworked by local impacts in post-Imbrian times.     

Heat transport by variable viscosity convection and implications for the Earth's thermal evolution

The case is presented that the efficiency of variable viscosity convection in the Earth's mantle to remove heat may depend only very weakly on the internal viscosity or temperature. An extensive numerical study of the heat transport by 2-D steady state convection with free boundaries and temperature dependent viscosity was carried out. The range of Rayleigh numbers (Ra) is 10⁴?10⁷ and the viscosity contrast goes up to 250000. Although an absolute or relative maximum of the Nusselt number (Nu) is obtained at long wavelength in a certain parameter range, at sufficiently high Rayleigh number optimal heat transport is achieved by an aspect ratio close to or below one. The results for convection in a square box are presented in several ways. With the viscosity ratio fixed and the Rayleigh number defined with the viscosity at the mean of top and bottom temperature the increase of Nu with Ra is characterized by a logarithmic gradient β = ?ln(Nu)/? ln(Ra) in the range of 0.23–0.36, similar to constant viscosity convection. More appropriate for a cooling planetary body is a parameterization where the Rayleigh number is defined with the viscosity at the actual average temperature and the surface viscosity is fixed rather than the viscosity ratio. Now the logarithmic gradient β falls below 0.10 when the viscosity ratio exceeds 250, and the velocity of the surface layer becomes almost independent of Ra. In an end-member model for the Earth's thermal evolution it is assumed that the Nusselt number becomes virtually constant at high Rayleigh number. In the context of whole mantle convection this would imply that the present thermal state is still affected by the initial temperature, that only 25–50% of the present-day heat loss is balanced by radiogenic heat production, and the plate velocities were about the same during most of the Earth's history.     

Stone movement on hillslopes in the Mojave Desert,California: A 16-year record

Previous research has shown that either hydraulic action or creep may be the dominant process transporting coarse debris down hillslopes in the American Southwest. This study analyses the movement over 16 years of painted stones on two hillslopes in the central Mojave Desert to ascertain which of these two processes dominate in this region. The distance moved (M) is found to be directly related to length of overland flow (X) and hillslope gradient (S), and inversely related to particle size (D). The fact that M is more highly correlated with X than with S suggests that hydraulic action rather than creep is the dominant process. It is concluded that this is probably the case over most of the Mojave and Sonoran Deserts on slopes up to at least 24°, and that it is only at higher elevations where winters are more severe that creep may become dominant.     

Deep structure of southeastern europe from Rayleigh waves

The analysis of Rayleigh-wave phase velocities up to about 250 s has allowed of deepening structural knowledge, down to several hundred kilometers underneath the triangular array formed by the WWSSN stations Athens-Istanbul-L'Aquila. For the path L'Aquila-Istanbul a lid-to-low velocity channel contrast of variable size is always present, while for the other two paths. Athens-Istanbul and Athens-L'Aquila. two alternative patterns are possible, one indicating the presence of a contrast between lid and low-velocity channel, the other suggesting the absence of significant layering down to depths of about 350 km.     

Beckenried viaduct: Foundation problems in a creeping slope

Summary The 3150 m long Beckenried viaduct traverses an unstable creeping, slope, the surface of the sound rock lying at depths from 10 to 60 m. Altogether 44 of the total 58 piers of the bridge founded on the sound rock had to be protected by shafts against the creeping soil and loosened rock layers. Based on geological explorations and previous monitoring of the slope displacements the clearance between the rectangular concrete piers and the elliptical shafts was specified to be 1.5 m in the dip direction of the slope and up to ±1.0 m in lateral direction. In order to avoid failure of the shafts due to the unusually large slope movements likely to occur during the service life of the viaduct, an entirely new design concept was applied. It involves flexible shafts consisting of four main parts, namely a rigid shaft collar, articulated ring elements, a rigid trapezoidal cylinder and basal displacement rings resting on the pier footing. Fundamentally, this design permits both: sliding of the shaft as a whole along particular slip surfaces in the loosened rock at depth but also differential displacements due to the creep of the soil strata above it. The sliding at the base contributes to 50% and more to the total surface movements. The shafts also serve as a permanent drainage system for the highly water sensitive slope material. The paper describes the criteria upon which the novel design of the individual shafts were made and also particular constructional details. After a construction period of only four years the bridge opened to traffic in December 1980. Observations made on the completed structure indicate a behaviour of the slope and the shafts which is well in accordance with the predictions.