One hundred fifty-year record of lead isotopes in Antarctic snow from Coats Land

A record of the concentrations of Pb and Ba and the isotopic composition of Pb has been established for a remote, low accumulation site in the Atlantic sector of Antarctica (Coats Land) by means of thermal ionization mass spectrometry. The snow samples cover the period ∼1840 to 1990. They were taken from the walls of a pit to a depth of 7.8 m and as a core to 16 m; ultraclean procedures were used. Detailed laboratory subsampling provided both long-term (secular scale) and short-term (intra-annual) Pb, Ba, and Pb isotope variations. The results show that there have been significant variations in Pb concentrations (range, 0.1 to 9.3 pg/g) and isotopic composition (range, 1.096 to 1.208 for ²⁰⁶Pb/²⁰⁷Pb ratio) since the 1840s. The data show evidence of pollution for this metal in Antarctica as early as the 1880s. Several Pb maxima were observed: the first at the beginning of the 20th century and the last in the 1970s to 1980s, with a clear decrease during recent years. Although the last maximum is clearly linked to the rise and fall in the use of leaded gasoline in the Southern Hemisphere, especially in South America, the reason for the first remains uncertain. The pattern of changing isotopic composition of Pb reveals the changing origin and character of the anthropogenic inputs to Antarctica. An interesting feature in this pattern is the relatively large contribution of unradiogenic Pb in the ∼1890s, possibly originating from Australia. Another interesting feature is the pronounced intra-annual variation in the isotopic composition of Pb, which illustrates the complexity of the changing inputs of Pb to Antarctica.     

Die Geschichte des Hydrobiologischen Laboratoriums in Kastanienbaum

Ohne Zusammenfassung     

Anisotropy of magnetic susceptibility in welded tuffs: application to a welded-tuff dyke in the tertiary Trans-Pecos Texas volcanic province,USA

Consideration of published anisotropy of magnetic susceptibility (AMS) studies on welded ignimbrites suggests that AMS fabrics are controlled by groundmass microlites distributed within the existing tuff fabric, the sum result of directional fabrics imposed by primary flow lineation, welding, and (if relevant) rheomorphism. AMS is a more sensitive indicator of fabric elements within welded tuffs than conventional methods, and usually yields primary flow azimuth estimates. Detailed study of a single densely welded tuff sample demonstrates that the overall AMS fabric is insensitive to the relative abundances of fiamme, matrix and lithics within individual drilled cores. AMS determinations on a welded-tuff dyke occurring in a choked vent in the Trans-Pecos Texas volcanic field reveals a consistent fabric with a prolate element imbricated with respect to one wall of the dyke, while total magnetic susceptibility and density exhibit axially symmetric variations across the dyke width. The dyke is interpreted to have formed as a result of agglutination of the erupting mixture on a portion of the conduit wall as it failed and slid into the conduit, followed by residual squeezing between the failed block and in situ wallrock. Irrespective of the precise mechanism, widespread occurrence of both welded-tuff dykes and point-welded, aggregate pumices in pyroclastic deposits may imply that lining of conduit walls by agglutionation during explosive volcanic eruptions is a common process.     

Interaction of mantle-derived magma with island crust? Trace element and oxygen isotope data from the Diego Hernandez Formation, Las Cañadas, Tenerife

The Quaternary Diego Hernandez Formation consists of interbedded phonolitic pyroclastics and basanite lavas and scoria beds. Most of the phonolites are mingled-magma units that contain a minor mafic component. The phonolites fall into two stratigraphically bounded groups, based on major and trace element abundances. Nb contents are especially distinctive, due to a varying role for titanite during petrogenesis. Nepheline syenite xenoliths, which are plentiful in some of the phonolitic ignimbrites, fall into the same two compositional groupings but are typically more strongly differentiated. Major and trace element variations during evolution of the phonolites can be modelled by fractional crystallization, by melting of syenite, or by some combination of the two such as AFC. Trace element variations among the basanites require the addition of a highly fractionated felsic component, either phonolitic magma or nepheline syenite. δ¹⁸O values of phonolites vary across twice the range of the basanites, inconsistent with an origin by pure fractional crystallization of a basanitic parent. We conclude that recycling of differentiated rocks within the Tenerife island edifice has played a significant role in Quaternary magmatism on Tenerife.     

TBT contamination identified in Antarctic marine sediments

We report for the first time butyltin contamination of near-shore sediments at six sites in the Ross Sea, Antarctica. A very high concentration of 2290 microg Sn kg(-1) sediment was recorded in one sample. The most likely source is abrasion of antifouling paint from the hulls of ice-breakers, but this pattern of contamination is also possible following ship groundings. Antifoulant biocides, such as TBT, have not been considered or detected in Antarctica previously and represent a new challenge to environmental managers and custodians.     

Variation in NbTa during differentiation of phonolitic magma,Tenerife, Canary Islands

Variation in $\text{Nb}\text{Ta}$ ratio through a suite of phonolitic volcanics is reported. Sphene, a phenocryst mineral, shows preferential incorporation of Ta relative to Mb, consistent with the bulk rock variation, where $\text{Nb}\text{Ta}$ increases with fractionation. Nb in these magmas may be partly present in the Nb³⁺ state.     

Tectonostratigraphic development of the Trondheim region Caledonides, Central Norway

The metamorphic allochthon of the central Norwegian Caledonides comprises a complex of discrete nappes of metasediments and igneous rocks ranging in age from probable Svecofennian through Vendian to Silurian. This southeastward-translated allochthon overlies a thin cover of autochthonous Vendian to Cambrian sediments deposited upon a crystalline Precambrian basement, and is superseded by late-orogenic, intermontanebasinal sediments of latest Silurian to Middle Devonian age. Stratigraphical sequences in higher allochthonous units are floored by oceanic tholeiitic basalts with rare, subjacent sheeted-dyke and gabbro units, considered as fragments of an ophiolite assemblage which suffered initial eastward transport in pre-Middle Arenig times, an important orogenic event which is well represented in northern and southwestern Norway. The overlying Ordovician—Silurian sequences, disturbed by episodic parorogenic events, embrace a variety of sedimentary facies from shallow-water carbonates to deep-marine terrigenous turbidites and include both island arc and marginal basin lavas and intrusives. Polyphase Middle Silurian metamorphism and deformation resulted in a complex telescoping and dissection of the Lower Palaeozoic rocks and their Precambrian substrate, with nappe translation in the order of several hundred kilometres. Folding and thrusting of Old Red Sandstone molasse sediments attests to continuing tectonism well into Devonian times.