Ar/Ar geochronology of the West Greenland Tertiary volcanic province

Paleocene volcanic rocks in West Greenland and Baffin Island were among the first products of the Iceland mantle plume, forming part of a larger igneous province that is now submerged beneath the northern Labrador Sea. A ⁴⁰Ar/³⁹Ar dating study shows that volcanism commenced in West Greenland between 60.9 and 61.3 Ma and that 80% of the Paleocene lava pile was erupted in 1 million years or less (weighted mean age of 60.5±0.4 Ma). Minimum estimates of magma production rates (1.3×10⁻⁴ km³ year⁻¹ km⁻¹) are similar to the present Iceland rift, except for the uppermost part of the Paleocene volcanic succession where the rate decreases to <0.7×10⁻⁴ km³ year⁻¹ km⁻¹ (rift). The timing of onset of volcanism in West Greenland coincides with the opening of the northern Labrador Sea and is also strikingly similar to the age of the oldest Tertiary volcanic rocks from offshore SE Greenland and the British–Irish province. This is interpreted as manifesting the impact and rapid (>1 m/year) lateral spreading of the Iceland plume head at the base of the Greenland lithosphere at 62 Ma. We suggest that the arrival, or at least a major increase in the flux, of the Iceland mantle plume beneath Greenland was a contributing factor in the initiation of seafloor spreading in the northern Labrador Sea. Our study has also revealed a previously unrecognised Early Eocene volcanic episode in West Greenland. This magmatism may be related to movement on the transform Ungava Fault System which transferred drifting from the Labrador Sea to Baffin Bay. A regional change in plate kinematics at 55 Ma, associated with the opening of the North Atlantic, would have caused net extension along parts of this fault. This would have resulted in decompression and partial melting of the underlying asthenosphere. The source of the melts for the Eocene magmatism may have been remnants of still anomalously hot Iceland plume mantle which were left stranded beneath the West Greenland lithosphere in the Early Paleocene.     

Analysis and application of a non-conventional underwater geoelectrical method in Lake Geneva,Switzerland

The electrical method presented is used for determining the resistivity of lake-bottom sediments and is based on the d.c. electrical sounding principles. The electrode array, called the fishing rod (FR), is of pole-pole type and is orientated vertically on a line perpendicular to the surface of the water. The technique is used for mapping resistivity anomalies located deep underwater. This paper presents an analysis of the resolution capabilities of the FR method and the results of a case study carried out in Lake Geneva, where measurements were interpreted using a one-dimensional (1D) multilayer earth model. The analysis of the uncertainty in the model parameters of a 1D multilayer earth model is carried out using the covariance matrix of the linearized inversion problem. The results of the analyses show that when the thickness and resistivity of the water layer is known, the resistivity of the sediment layer is well determined under most circumstances. The thickness of the sediment layer is well determined when resistivity contrasts are not too low. In Lake Geneva the FR method has been used to study an old depression with a resistive channel. This application shows the efficiency of the method compared with conventional electrical methods, where water depth becomes a limiting factor. The use of an automated iterative inversion scheme in this particular case is advantageous, as a joint interpretation of the three different data sets measured with the FR method can be carried out. Finally, the result of the inversion is compared with the trial-and-error interpretations of a previous study.     

Isotopic age and metamorphic history of the banded gneiss at Danmarkshavn,East Greenland

Along the northern part of the East Greenland coast the Caledonian structures are superimposed on an older fold system called the Carolinidian. Traces of this Carolinidian belt are preserved in a few isolated fragments within the Caledonian fold belt. According to Haller (1970) one of these fragments exhibiting the typical Carolinidian NNW to NW-trending infrastructural folds is the peninsula of Germania Land which is accessible near the Danish weather station Danmarkshavn. The rock sampled there is a banded gneiss of granodioritic composition with steeply inclined, NNW-trending layers. Isotopic age determinations yielded essentially two groups of ages: 1) 3,000±150 m.y. (zircon suite and Rb/Sr whole rock analyses of layers) and 2) 320–380 m.y. (Rb/Sr mineral isochrons, U-Th-Pb on sphene, K/Ar on hornblende and biotite). The egg-shaped zircons support a sedimentary origin of the banded gneiss and in conjunction with the Rb/Sr whole rock ages determine the age of formation of the banded gneiss (or its last high grade metamorphism) some 3,000 m.y. ago. No other Precambrian metamorphism or orogeny is recorded in the rock. The ages between 320–380 m.y. date a thermal event of lower amphibolite facies grade related to a late Caledonian spasm.The new isotopic data reveal the existence of very old rocks in the hinterland — away from the direction of thrusting—of the East Greenland Caledonian belt. With respect to the age of the Carolinidian fold system three geological interpretations are compatible with the results of this study:

Non-Stoichiometric magnesian spinels in shale xenoliths from a native iron-bearing andesite at Asuk,Disko, central West Greenland

A strongly reduced native iron-bearing andesite breccia from Disko contains graphite-rich modified shale xenoliths with magnesian spinels. These spinels are free from or very poor in ferric iron and vary considerably within the MgO-FeO-Cr₂O₃-Al₂O₃ compositional space. Through a simple substitution of the type 3 (Mg, Fe)²⁺ ⇆ 2(Al, Cr)³⁺+□_vacancy, the spinels vary from stoichiometric (Mg, Fe)²⁺ (Al, Cr)³⁺ ₂O₄ towards (Al, Cr)₂O₃. The simple substitution of Cr for Al suggests that Cr was accepted into the spinel structure as Cr³⁺, despite the reduced nature of the enclosing andesite. The most magnesian spinels are cation deficient spinel_ss in the synthetic systems MgO-Al₂O₃ and MgO-Al₂O₃-Cr₂O₃. The absence of exolved (Al, Cr)₂O₃-component is probable due to rapid quenching.     

Industrial minerals and rocks, aggregates and natural stones in the Nordic countries

The Nordic countries, including Greenland, have a long tradition in mining. The industrial minerals sector is expanding in most Nordic countries and extensive development has taken place during the last few years. The main commodities mined are carbonate rocks, quartz, feldspar, apatite, olivine and talc.
A number of diferent types of dimension stones are quarried in all countries. Rock aggregates are increasingly important, replacing sand and gravel aggregate as construction materials in some countries due to the need to protect ground water supplies.     

An in-depth look at the lunar crater Copernicus: Exposed mineralogy by high-resolution near-infrared spectroscopy

Newly acquired, sequentially spaced, high-resolution near-infrared spectra across the central section of crater Copernicus’ interior have been analyzed using a range of complementary techniques and indexes.We have developed a new interpretative method based on a multiple stage normalization process that appears to both confirm and expand on previous mineralogical estimations and mapping. In broad terms, the interpreted distribution of the principle mafic species suggests an overall composition of surface materials dominated by calcium-poor pyroxenes and minor olivine but with notable exceptions: the southern rim displays strong ca-rich pyroxene absorption features and five other locations, the uppermost northern crater wall, opposite rim sections facing the crater floor, and the central peak Pk1 and at the foot of Pk3, show instead strong olivine signatures.We also propose impact glass an alternative interpretation to the source of the weak but widespread olivine-like spectral signature found in low-reflectance samples, since it probably represents a major regolith constituent and component in large craters such as Copernicus.The high quality and performance of the SIR-2 data allows for the detection of diagnostic key mineral species even when investigating spectral samples with very subdued absorption features, confirming the intrinsic high-quality value of the returned data.     

Joint inversion of temperature,vitrinite reflectance and fission tracks in apatite with examples from the eastern North Sea area

As sediment accumulation indicates basin subsidence, erosion often is understood as tectonic uplift, but the amplitude and timing may be difficult to determine because the sedimentary record is missing. Quantification of erosion therefore requires indirect evidence, for example thermal indicators such as temperature, vitrinite reflectance and fission tracks in apatite. However, as always, the types and quality of data and the choice of models are important to the results. For example, considering only the thermal evolution of the sedimentary section discards the thermal time constant of the lithosphere and essentially ignores the temporal continuity of the thermal structure. Furthermore, the types and density of thermal indicators determine the solution space of deposition and erosion, the quantification of which calls for the use of inverse methods, which can only be successful when all models are mutually consistent. Here, we use integrated basin modelling and Markov Chain Monte Carlo inversion of four deep boreholes to show that the erosional pattern along the Sorgenfrei–Tornquist Zone (STZ) in the eastern North Sea is consistent with a tectonic model of tectonic inversion based on compression and relaxation of an elastic plate. Three wells in close proximity SW of the STZ have different data and exhibit characteristic differences in erosion estimates but are consistent with the formation of a thick chalk sequence, followed by minor Cenozoic erosion during relaxation inversion. The well on the inversion ridge requires ca. 1.7 km Jurassic-Early Cretaceous sedimentation followed by Late Cretaceous–Palaeocene erosion during inversion. No well demands thick Cenozoic sedimentation followed by equivalent significant Neogene exhumation. When data are of high quality and models are consistent, the thermal indicator method yields significant results with important tectonic and geodynamic implications.     

Analysis of coprolites from the extinct mountain goat Myotragus balearicus

Humans colonized the Balearic Islands 5–4 ka ago. They arrived in a uniquely adapted ecosystem with the Balearic mountain goat Myotragus balearicus (Bovidae, Antilopinae, Caprini) as the only large mammal. This mammal went extinct rapidly after human arrival. Several hypotheses have been proposed to explain the extinction of M. balearicus. For the present study ancient DNA analysis (Sanger sequencing, Roche-454, Ion Torrent), and pollen and macrofossil analyses were performed on preserved coprolites from M. balearicus, providing information on its diet and paleo-environment. The information retrieved shows that M. balearicus was heavily dependent on the Balearic box species Buxus balearica during at least part of the year, and that it was most probably a browser. Hindcast ecological niche modelling of B. balearica shows that local distribution of this plant species was affected by climate changes. This suggests that the extinction of M. balearicus can be related to the decline and regional extinction of a plant species that formed a major component of its diet. The vegetation change is thought to be caused by increased aridity occurring throughout the Mediterranean. Previous hypotheses relating the extinction of M. balearicus directly to the arrival of humans on the islands must therefore be adjusted.