Geological Survey of Sweden

About: Geological Survey of Sweden is a government organization based out in Uppsala, Sweden. It is known for research contribution in the topics: Metamorphism & Zircon. The organization has 316 authors who have published 671 publications receiving 18333 citations. The organization is also known as: Sveriges Geologiska Undersökning.

Floating stones off El Hierro, Canary Islands: xenoliths of pre-island sedimentary origin in the early products of the October 2011 eruption

Abstract: . A submarine eruption started off the south coast of El Hierro, Canary Islands, on 10 October 2011 and continues at the time of this writing (February 2012). In the first days of the event, peculiar eruption products were found floating on the sea surface, drifting for long distances from the eruption site. These specimens, which have in the meantime been termed "restingolites" (after the close-by village of La Restinga), appeared as black volcanic "bombs" that exhibit cores of white and porous pumice-like material. Since their brief appearance, the nature and origin of these "floating stones" has been vigorously debated among researchers, with important implications for the interpretation of the hazard potential of the ongoing eruption. The "restingolites" have been proposed to be either (i) juvenile high-silica magma (e.g. rhyolite), (ii) remelted magmatic material (trachyte), (iii) altered volcanic rock, or (iv) reheated hyaloclastites or zeolite from the submarine slopes of El Hierro. Here, we provide evidence that supports yet a different conclusion. We have analysed the textures and compositions of representative "restingolites" and compared the results to previous work on similar rocks found in the Canary Islands. Based on their high-silica content, the lack of igneous trace element signatures, the presence of remnant quartz crystals, jasper fragments and carbonate as well as wollastonite (derived from thermal overprint of carbonate) and their relatively high oxygen isotope values, we conclude that "restingolites" are in fact xenoliths from pre-island sedimentary layers that were picked up and heated by the ascending magma, causing them to partially melt and vesiculate. As they are closely resembling pumice in appearance, but are xenolithic in origin, we refer to these rocks as "xeno-pumice". The El Hierro xeno-pumices hence represent messengers from depth that help us to understand the interaction between ascending magma and crustal lithologies beneath the Canary Islands as well as in similar Atlantic islands that rest on sediment-covered ocean crust (e.g. Cape Verdes, Azores). The occurrence of "restingolites" indicates that crustal recycling is a relevant process in ocean islands, too, but does not herald the arrival of potentially explosive high-silica magma in the active plumbing system beneath El Hierro.

The evolution of a uranium province in northern sweden

Abstract: The Arjeplog-Arvidsjaur uranium province contains epigenetic uranium deposits formed at the culmination of Svecofennian orogenesis at about 1750 Ma ago, stratabound deposits in subsequent volcanics and enhanced uranium contents in a wide variety of rock types. The province is situated along the southern margin of an early Proterozoic continent and may have been underlain both by older basement and, more speculatively, by a subduction zone. The movement of uranium is clearly related to processes of magmatism and metamorphism during the Svecofennian orogenesis. Pre-Svecofennian basement is a potential source of uranium.

A summary of Caledonian front stratigraphy, northern Jämtland/southern Västerbotten, central Swedish Caledonides

Abstract: The sedimentary rocks of the Caledonian front in northern Jamtland and southernmost Vasterbotten described here include late Pre-Cambrian, Cambrian and Ordovician sequences occurring beneath the metamorphic allochthon of the Seve-Koli Nappe Complex. Three groups are recognized. The lowest, the Risback Group (c. 700 m) includes four formations in the type area, dominated by alluvial sandstones. Tillites (Varangian) and a quartzite-shale formation compose the overlying Sjoutalven Group (c. 300 m), which ranges into the Middle Cambrian. The overlying Tasjon Group (c. 250 m) contains a lower black shale and an upper greywacke-dominated formation, ranging in age from the Middle Cambrian into the Middle Ordovician. The full succession, represented in the west, thins eastwards, and in the autochthon only the uppermost part of the Sjoutalven and the Tasjon Group are present. The paper briefly discusses the correlation of the three groups elsewhere in the Caledonides.