The water and trace element contents of melt inclusions across an active subduction zone

Water concentrations of olivine-hosted melt inclusions show no consistent variation across the northern part of the Central American subduction zone in southeastern Guatemala. Magmatic water contents remain moderately high (~2 wt%) throughout the back-arc region. Melt inclusions from some of these back-arc basalts also have notably high CO₂ contents (>900 ppm CO₂). The B and B/Ce ratios of melt inclusions systematically decline across the arc, the first parameters to exhibit systematic changes across southeastern Guatemala. It appears, therefore, that dehydration-driven, flux-melting persists across the arc, although decompression melting is of approximately equal importance in the back-arc region. Dehydration of the slab/wedge region is regarded as semi-continuous down-dip, to depths of at least 175–200 km. Moderate water contents are maintained by stepwise dehydration reactions, while truly incompatible fluid mobile elements are progressively stripped from the Cocos plate. The notably high CO₂ contents of some back-arc basalts may indicate increasing devolatilization of subducted carbonate sediments with slab depth. The moderate H₂O contents of back-arc basaltic magmas has likely contributed to their early fractionation of clinopyroxene around the Moho.Editorial responsibility: T.L. Grove     

The final phase of dead-ice moraine development: processes and sediment architecture, Kötlujökull, Iceland

Consecutive phases of de-icing of ice-cored moraines and the formation of dead-ice moraine were monitored over a 4-year period at the terminus of the Kötlujökull glacier, Iceland. Particularly, the transition from partially ice-cored moraine with isolated dead-ice blocks to the ice-free landscape receives attention in this paper in order to link the final melting processes to the architecture of the sedimentary end product. In the current humid sub-polar climate of south Iceland de-icing of partially ice-cored moraines results chiefly from melting along the bottom surface of ice-cores with an annual average rate of 25 cm. The final de-icing is associated with an interrelated group of re-sedimentation processes and surface features. Series of sinkholes evolve at the toe of dead-ice blocks, which initiate retrogressive rotational sliding or backslumping of the ice-cored slopes and the formation of distinct edges and fractures in the adjacent basins. Although backslumping is the dominant process in this phase of re-sedimentation, structures resulting from this process are rarely recognized in the ice-free landscape. As ice-cores gradually diminish the effect of the latest re-sedimentation events will overprint or destroy most existing sedimentary characteristics. Thus, in the ice-free landscape, structures mainly related to the formation of sinkholes and fractures remain imprinted on the sediment succession. Generally, no inversion of the topography occurs during the final phase of de-icing. The overall topography recognized in the late phase of the fully ice-cored terrain is merely lowered and the amplitude of the relief reduced as de-icing progresses. The sediment architecture of the ice-free landscape is characterized by heterogeneous and often slumped diamict sediments with variable thickness and lateral distribution; clast orientation is related to the direction of slopes, and boulders are found in isolated groups or in linear arrangements.     

Reference Minerals for the Microanalysis of Light Elements

The quantitative determination of light element concentrations in geological specimens represents a major analytical challenge as the electron probe is generally not suited to this task. With the development of new in situ analytical techniques, and in particular the increasing use of secondary ion mass spectrometry, the routine determination of Li, Be and B contents has become a realistic goal. However, a major obstacle to the development of this research field is the critical dependence of SIMS on the availability of well characterized, homogeneous reference materials that are closely matched in matrix (composition and structure) to the sample being studied. Here we report the first results from a suite of large, gem crystals which cover a broad spectrum of minerals in which light elements are major constituents. We have characterized these materials using both in situ and wet chemical techniques. The samples described here are intended for distribution to geochemical laboratories active in the study of light elements. Further work is needed before reference values for these materials can be finalized, but the availability of this suite of materials represents a major step toward the routine analysis of the light element contents of geological specimens.     

The hydrogeochemistry of the Kärkevagge Valley, Lapland, Sweden

The Kärkejokk (jokk = Lappish for brook) is rich in sulfate and calcium, both elements having been considered enigmatic. To resolve these problems we collected waters at 13 sites during 27 June to 1 September 1996. Nine sites were in the Kärkevagge, and the others in the drainage towards lake Torne Träsk. Rain waters were collected the same period. Conductivity, pH, and temperature were measured in the field, whereas salt load and the elements Na, K, Ca, Mg, S, Si, Fe, Al, Mn, Zn, Sr, and Ba were determined in the laboratory.
Mixing models based on rain water and leaching products of the major bedrocks do not explain observed element patterns except in the lower parts of the jokk. However, oxidation of pyrite has formed acid, sulfate–rich solutions that released Ca and Mg from limestones, and Fe, Mn, Al, and Si, from black shales (Malmsten 1998; Malmsten et al. 2000). Conservative mixing models, using rain water, leached bedrock and pyrite, match the jokk waters quite well, and sulfur isotope data corroborate these findings. The nearby Låktajokk, and Vassijokk also contain much S.
Where these waters debouch they may deposit Si, Al, and Ca, but only little S on various rocks. Total rock analyses, thermodynamic and X–ray data suggest that gypsum, barite, or alunite are not formed in major quantities.
These models show that the hydrogeochemistry of the Kärkejokk may be less enigmatic than often assumed.     

The Urquiola oil spill,La Coruña,Spain: Case history and discussion of methods of control and clean-up

A massive oil spill affected approximately 215 km of coastline as a result of the grounding and subsequent explosion of the supertanker Urquiola at the entrance to the harbour at La Coruña, Spain, on 12 May 1976. A total of 99–100 000 tons of Persian Gulf crude oil was lost, most of which burned, but an estimated 25–30 000 tons washed ashore. Over 2000 tons of dispersants were applied to the oil at sea. Land-based clean-up and control methods were largely inadequate to combat the spread of oil, and were ineffective at preventing large scale environmental damage.     

Die Verfeinerung der Kristallstrukturen von PbCl2 (Cotunnit), BaCl2, PbSO4 (Anglesit) und BaSO4 (Baryt)

Contributions to Mineralogy and Petrology - Das 2-wertige Blei und das 2-wertige Barium kommen in einander entsprechenden Verbindungen sowohl gleich als auch unterschiedlich koordiniert vor. Die...     

Die ≪Strahlung≫ bei Pouillet und Kirchhoff

Zusammenfassung Der Widerspruch zwischen den Strahlungsgesetzen der Physik und der Definition der Strahlung durchPouillet, die allen bisherigen Strahlungs-Messungen zu Grunde liegt, wird am Modell des schwarzstrahlenden Hohlraums vonKirchhoff gezeigt. Auch die Bestimmungen der Solarkonstante (Kalitins's Liste) sind verloren.

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Summary The contradiction ofPouillet's radiation and the physical laws of radiation sinceKirchhoff, Boltzmann-Stefan, Wien, Lummer andKurlbaum is by the model of the black radiating body ofKirchhoff demonstrated. The measurements of radiation have followed til now to the antiquated idea ofPouillet. The determination of the solar constant as inKalitin's list represented also is lost.

     

Carbon-13 NMR spectra of macerals separated from individual coals

The density gradient centrifugation technique has recently been applied to the separation of macerals from whole coals. Sufficient quantities have been separated to permit examination of pure exinite, vitrinite and inertinite fractions by combined cross polarization and magic angle sample spinning (CP/MASS) carbon-13 NMR techniques. The similarities and differences observed in the maceral groups of two coals are discussed. Diversity in precursors or in differential chemical maturation or a combination of both of these factors can be used to account for subtle spectral differences in the two coals and macerals studied even though the gross spectral features are very similar for a given maceral type. The data show that CP/MASS is a technique that can address such interesting geochemical questions.     

First terrestrial occurrence of roedderite in volcanic ejecta of the Eifel,Germany

Idiomorphic crystals of roedderite occur in melt-coated cavities of xenoliths of contact-altered quartz-sillimanite and quartz-feldspar gneisses which were ejected with the tephritic lava of the Bellerberg volcano. Physical and chemical properties of three different sets of crystals agree generally with those of roedderites from meteorites, in which so far the mineral had been found exclusively. In detail, however, there are characteristic chemical differences amongst the Eifel roedderites with one set of crystals matching closely the ideal formula (Na,K)₂Mg₅ Si₁₂O₃₀, a second set containing excess alkalies according to the substitution Na⁺0.5 Mg²⁺, and a third set richer in iron having an alkali deficiency following Fe³⁺Fe²⁺+Na⁺.The terrestrial roedderites are considered to be precipitates from highly alkaline, MgSi-rich, but Aldeficient gas phases that evolved through contact heating of the gneisses by the tephrite magma.