MgAl2O4 spinels from Allende and NWA 763 carbonaceous chondrites: Structural refinement,cooling history,and trace element contents

MgAl₂O₄ spinels from Allende and NWA 763 carbonaceous chondrites were studied by X‐ray single crystal diffraction, SEM, electron microprobe, LA‐ICP‐MS, and Raman spectroscopy. Those from Allende are almost pure, but, in one case, we found a strong FeO_tot zonation. Spinels from NWA 763 show Mg‐Fe²⁺ substitutions. Almost pure MgAl₂O₄ spinels from both meteorites underwent slow cooling and reached their intracrystalline closure temperature (T_c) in the range 460–520 °C. The NWA 763 spinel with higher FeO content shows a T_c of about 720 °C. X‐ray single crystal diffraction and Raman spectroscopy suggest a slow cooling and an ordered structure with trivalent cations in M site and divalent in T site. Among the trace elements, Ti and Co are enriched with respect to the terrestrial analogs, while Mn, Ni, and Sn show intermediate values between different terrestrial occurrences. Vanadium cannot be used as a tracer of extraterrestrial origin as for Cr‐spinels, because its content is similar in extraterrestrial and terrestrial spinels. In the zoned crystal from Allende, Co show a strong zonation similar to that of FeO.     

Application of the Lorenz equations for studying thermal convection in the lithosphere

Stationary solutions including wave solutions with constant amplitudes are found for nonlinear equations of thermal convection in a layer with nonlinear rheology. The solution is based on the Fourier expansion of unknown velocities and temperatures with only the first and first two terms retained in the velocity and temperature series, respectively. This method, which can be regarded as the Lorenz method, yields the Lorenz equations that fairly well describe the thermal convection in a layer with Newtonian rheology if the Rayleigh number is not very large. The obtained generalization of the Lorenz equations to the case of an integral (having a memory) nonlinear rheology implies that only the first term is retained in the Fourier series for the stress components, i.e., the nonlinear rheological equation is harmonically linearized. However, in the Fourier series of temperature, it is essential to keep the second term: this term, which is independent of the horizontal coordinate, models the thermal boundary layer that characterizes the developed convection. We constructed the bifurcation curves that describe the stationary convection in the nonlinear integral medium simulating the rheology of the mantle, and analyzed the stability of stationary convective flows. The Lorenz method is applied to study small-scale thermal convection in the lithosphere of the Earth.     

Meteorological observations 2006 and ground temperature variations over 12-year at the Sermilik Station,Ammassalik Island,Southeast Greenland

Geografisk Tidsskrift, Danish Journal of Geography 108(1):153–161, 2008

Meteorological stations have been in operation since 1993 at the Sermilik Research Station (65°40′N, 38°10′W), Ammassalik Island, Southeast Greenland. This note presents meteorological observations for the calendar year 2006 from the two meteorological stations: Station Nunatak (515 m a.s.l.) and Station Coast (25 m a.s.l.). The year 2006 record is not complete due to a temporal break down of Station Coast (from end-of June through beginning of August). Special focus is given to ground temperature measurements at the meteorological Station Nunatak (1994–2006) 0.1 and 0.3 m below the surface. Data are presented to illustrate the intra- and inter-annual temperature variability and possible trends in the upper part of the soil.     

Towards an integrated arid zone water management using simulation-based optimisation

For ensuring both optimal sustainable water resources management and long-term planning in a changing arid environment, we propose an integrated Assessment-, Prognoses-, Planning- and Management tool (APPM). The new APPM integrates the complex interactions of the strongly nonlinear meteorological, hydrological and agricultural phenomena, considering the socio-economic aspects. It aims at achieving best possible solutions for water allocation, groundwater storage and withdrawals including saline water management together with a substantial increase of the water use efficiency employing novel optimisation strategies for irrigation control and scheduling. To obtain a robust and fast operation of the water management system, it unites process modeling with artificial intelligence tools and evolutionary optimisation techniques for managing both water quality and quantity. We demonstrate some key components of our methodology by an exemplary application to the south Al-Batinah region in the Sultanate of Oman which is affected by saltwater intrusion into a coastal aquifer due to excessive groundwater withdrawal for irrigated agriculture. We show the effectiveness and functionality of a new simulation-based water management system for the optimisation and evaluation of different irrigation practices, crop pattern and resulting abstraction scenarios. The results of several optimisation runs indicate that due to contradicting objectives, such as profit-oriented agriculture versus aquifer sustainability only a multi-objective optimisation can provide sustainable solutions for the management of the water resources in respect of the environment as well as the socio-economic development.     

Shocked chromites in fossil L chondrites: A Raman spectroscopy and transmission electron microscopy study

Chromites from Middle Ordovician fossil L chondrites and from matrix and shock‐melt veins in Catherwood, Tenham, and Coorara L chondrites were studied using Raman spectroscopy and TEM. Raman spectra of chromites from fossil L chondrites showed similarities with chromites from matrix and shock‐melt veins in the studied L chondrite falls and finds. Chromites from shock‐melt veins of L chondrites show polycrystallinity, while the chromite grains in fossil L chondrites are single crystals. In addition, chromites from shock‐melt veins in the studied L chondrites have high densities of planar fractures within the subgrains and many subgrains show intergrowths of chromite and xieite. Matrix chromite of Tenham has similar dislocation densities and planar fractures as a chromite from the fossil meteorite Golvsten 001 and higher dislocation densities than in chromite from the fossil meteorite Sextummen 003. Using this observation and knowing that the matrix of Tenham experienced 20–22 GPa and <1000° C, an upper limit for the P,T conditions of chromite from Golvsten 001 and Sextummen 003 can be estimated to be 20–22 GPa and 1000° C (shock stage S3–S6) and 20 GPa and 1000° C (S3–S5), respectively, and we conclude that the studied fossil meteorite chromites are from matrix.     

Accumulation of elastic strains in the upper crust on the locked transform faults and the tectonomagnetic effect

Plate tectonics only allows small deformations in the lithospheric plates. The laboratory experiments with the rock specimens show that the creep is transient when the creep strain is at most 1%. Hence, if we assume that the creep strain in the lithospheric plates is below this threshold, the creep is transient. The present paper addresses the role of the elastic, brittle (pseudo-plastic), and creep rheology of the lithosphere during the accumulation of elastic shear strains on the locked faults in the Earth’s crust, i.e., during the process of preparation of the earthquakes. The effective viscosity characterizing the transient creep is lower than that under the steady-state creep and it depends on the characteristic time of a given process. The characteristic duration of the stress and strain accumulation process in the vicinity of the locked faults is a few dozen years. On these time intervals, the thin upper crustal layer behaves as brittle; the underlying layer behaves as elastic (it is just this layer which accommodates stress accumulation leading to the earthquake), whereas the transient creep is predominant in the lower crust and mantle lithosphere. Transient creep entails nonlinear time dependence of the strains arising in the vicinity of the locked fault in the elastic crust. The perturbations in the magnetic field induced by these strains can be treated as the magnetic precursor of the earthquake.     

Diskussionsbemerkungen zum Problem der Maßstäbe und Kriterien für die Bewertung der Abwasserbelastung und des Zustandes natürlicher Gewässer

Ohne Zusammenfassung Von der Redaktion ausgew?hlt aus einem l?ngeren Diskussionsvotum.     

Die Blei-Zinkerzlagerstätten des Pflerschtals

The stratabound lead zinc ore deposits of the Pflersch Valley (Eastern Alps) are intercalated in pre-Triassic folded and metamorphosed pelitic sediments of the ötztal-Stubaier Masse. The ores (sphalerite, galena, pyrrhotite etc.) are stratigraphically controled by graphitic shists and tuffitic layers. The thickness of the ore bodies varies between some centimeters to some meters. As part of the regional setting these orebearing strata were metamorphosed during several metamorphic episodes together with these metasediments. Field observations, supplimented by microscopic studies, and the calculation of p-T-conditions indicate that now partly mobilized ores probably had their origin during the last pre-Triassic metamorphic events. These ores probably came in part as sulfide melts. There seems also a possibility of an additional alpine ore mobilization process. On the basis of age determinations and petrographic studies carried out in the ötztal-Stubaier Masse by other authors it is possible to say that the ore-bearing former sediments belong to Silurian or even pre-Silurian age (>410my).