The north-subducting Rheic Ocean during the Devonian: consequences for the Rhenohercynian ore sites

Base metal mining in the Rhenohercynian Zone has a long history. Middle-Upper Devonian to Lower Carboniferous sediment-hosted massive sulfide deposits (SHMS), volcanic-hosted massive sulfide deposits (VHMS) and Lahn-Dill-type iron, and base metal ores occur at several sites in the Rhenohercynian Zone that stretches from the South Portuguese Zone, through the Lizard area, the Rhenish Massif and the Harz Mountain to the Moravo-Silesian Zone of SW Bohemia. During Devonian to Early Carboniferous times, the Rhenohercynian Zone is seen as an evolving rift system developed on subsiding shelf areas of the Old Red continent. A reappraisal of the geotectonic setting of these ore deposits is proposed. The Middle-Upper Devonian to Early Carboniferous time period was characterized by detrital sedimentation, continental intraplate and subduction-related volcanism. The large shelf of the Devonian Old Red continent was the place of thermal subsidence with contemporaneous mobilization of rising thermal fluids along activated Early Devonian growth faults. Hydrothermal brines equilibrated with the basement and overlying Middle-Upper Devonian detrital deposits forming the SHMS deposits in the southern part of the Pyrite Belt, in the Rhenish Massif and in the Harz areas. Volcanic-hosted massive sulfide deposits (VHMS) formed in the more eastern localities of the Rhenohercynian domain. In contrast, since the Tournaisian period of ore formation, dominant pull-apart triggered magmatic emplacement of acidic rocks, and their metasomatic replacement in the apical zones of felsic domes and sediments in the northern part of the Iberian Pyrite belt, thus changing the general conditions of ore precipitation. This two-step evolution is thought to be controlled by syn- to post- tectonic phases in the Variscan framework, specifically by the transition of geotectonic setting dominated by crustal extension to a one characterized by the subduction of the supposed northern slab of the Rheic Ocean preceding the general Late Variscan crustal shortening and oroclinal bending

European Atlas of Natural Radiation

Natural ionizing radiation is considered as the largest contributor to the collective effective dose received by the world population. The human population is continuously exposed to ionizing radiation from several natural sources that can be classified into two broad categories: high-energy cosmic rays incident on the Earth’s atmosphere and releasing secondary radiation (cosmic contribution); and radioactive nuclides generated during the formation of the Earth and still present in the Earth’s crust (terrestrial contribution). Terrestrial radioactivity is mostly produced by the uranium and thorium radioactive families together with potassium. In most circumstances, radon, a noble gas produced in the radioactive decay of uranium, is the most important contributor to the total dose. This Atlas aims to present the current state of knowledge of natural radioactivity, by giving general background information, and describing its various sources. This reference material is complemented by a collection of maps of Europe displaying the levels of natural radioactivity caused by different sources. It is a compilation of contributions and reviews received from more than 80 experts in their field: they come from universities, research centres, national and European authorities and international organizations. This Atlas provides reference material and makes harmonized datasets available to the scientific community and national competent authorities. In parallel, this Atlas may serve as a tool for the public to: • familiarize itself with natural radioactivity; • be informed about the levels of natural radioactivity caused by different sources; • have a more balanced view of the annual dose received by the world population, to which natural radioactivity is the largest contributor; • and make direct comparisons between doses from natural sources of ionizing radiation and those from man-made (artificial) ones, hence to better understand the latter.JRC.G.10-Knowledge for Nuclear Security and Safet

European Atlas of Natural Radiation

Natural ionizing radiation is considered as the largest contributor to the collective effective dose received by the world population. The human population is continuously exposed to ionizing radiation from several natural sources that can be classified into two broad categories: high-energy cosmic rays incident on the Earth’s atmosphere and releasing secondary radiation (cosmic contribution); and radioactive nuclides generated during the formation of the Earth and still present in the Earth’s crust (terrestrial contribution). Terrestrial radioactivity is mostly produced by the uranium and thorium radioactive families together with potassium. In most circumstances, radon, a noble gas produced in the radioactive decay of uranium, is the most important contributor to the total dose.This Atlas aims to present the current state of knowledge of natural radioactivity, by giving general background information, and describing its various sources. This reference material is complemented by a collection of maps of Europe displaying the levels of natural radioactivity caused by different sources. It is a compilation of contributions and reviews received from more than 80 experts in their field: they come from universities, research centres, national and European authorities and international organizations.This Atlas provides reference material and makes harmonized datasets available to the scientific community and national competent authorities. In parallel, this Atlas may serve as a tool for the public to: • familiarize itself with natural radioactivity;• be informed about the levels of natural radioactivity caused by different sources;• have a more balanced view of the annual dose received by the world population, to which natural radioactivity is the largest contributor;• and make direct comparisons between doses from natural sources of ionizing radiation and those from man-made (artificial) ones, hence to better understand the latter.Additional information at: https://remon.jrc.ec.europa.eu/About/Atlas-of-Natural-Radiatio

Alkalibasaltische Intrusionen im Devon der Lahnmulde (südliches Rheinisches Schiefergebirge)

Schichtkonkordante Intrusionen basischer Schmelzen sind im Paläozoikum der südwestlichen Lahnmulde verhältnismäßig rar. Im Gegensatz zu den zahlreichen metatholeiitischen Lagergängen der mittleren und östlichen Lahnmulde, die zumindest größtenteils unterkarbonischen Alters sind, handelt es sich hierbei um ehemalige Alkalibasalte des Givets. Diese werden in ihrer geologischen Stellung, mineralogisch-petrographischen Zusammensetzung und geochemischen Entwicklung beschrieben. Ihre Merkmale, insbesondere ihr Verhalten während der Differentiation, werden herausgestellt und gegenüber den tholeiitischen Intrusionen abgegrenzt. Ihre geotektonische Position wird kurz diskutiert.Abstract: Sills of basic chemistry are comparitively rare within the Palaeozoic of the southwestern Lahn syncline. They are exclusively of alkali basalfic origin of Givetian age and contrast in thaf fo the rather frequent meta-fholeiitic sills of the middle and easfern Lahn syncline which are at least mainly of Carboniferous age. The meta-alkali basaltic sills are described in their geological setting as well as in their mineralogy, petrography, and geochemistry. Their characteristics, especially their development during differentiation are outlined and compared with those of meta-tholeiitic sills. The geotectonic setting of the meta-alkali basaltic sills is briefly discussed.researc

Clay mineral formation in Permian rocks of a geothermal borehole at Northern Upper Rhine Graben, Germany

Hydrothermally altered rhyolite rocks in the Permian Donnersberg Formation of a geothermal borehole in the Northern Upper Rhine Graben (Germany) were investigated to find out answers for the low hydraulic conductivity of the rocks. The composition of clay minerals and the temperature of smectite–illite transformation were carried out using X-ray diffraction, X-ray fluorescence, transmission electron microscopy, Fourier transform infrared spectroscopy, and polarized-light microscopy analyses. Clay mineral (CM) composition includes illite/muscovite (1M and 2M1 polytypes), illite–smectite interstratifications (IS-ml), smectite, and chlorite; and non-clay minerals such as quartz, feldspars, epidote, calcite, dolomite, and hematite were detected. The 2M1-polytype mica might be the only primary sheet silicates from the parent rocks, while the others occur as authigenic neo-formed CMs under heat flow and geothermal gradient. The development of CMs indicates different mechanisms of illitization and smectitization. Based on the texture, morphology, structure/polytype, and chemistry of rocks and minerals, in particular CMs, the study grouped the CM formation into three transformation processes: smectitization during magma cooling and possible contact metamorphisms with decreasing and low temperature, smectite illitization controlled by burial diagenesis and hydrothermal alteration, and illite smectitization followed exhumation and Cenozoic subsidence with decreasing temperature. The rhyolites were altered to all of the orders IS-R0, IS-R1, and IS-R3 by the dissolution-precipitation and layer-to-layer mechanisms. The first one supported small xenomorphic plates and flakes of 1Md, elongated particles of 1M, and pseudo-hexagonal forms of 2M1. The second one could lead to the platy particles of 1Md and 2M1 polytypes. The dominant temperature range for the transformation in the area has been 140–170 °C– ~ 230 °C.Technische Universität Darmstadt (3139

The Carboniferous in the Stratigraphic Table of Germany 2016

The Carboniferous timescale in the Stratigraphic Table of Germany 2016 (STD 2016) relies on slightly modified composite ages already used in the Stratigraphic Table of Germany 2002 (STD 2002). They differ from the Geological Time Scale 2012 (GTS 2012). Besides the international stages, the western European Mississippian regional stages are shown. The traditional German subdivision of the Kulm was discarded. Mississippian (lower Carboniferous) sedimentary successions are widespread in the mountainous regions and hills in the central part of Germany (Rhenish Mountains, Harz, Thuringian Forest, Franconian Forest and adjoining regions of Saxony). They are also widespread in the subsurface of Northern Germany. Paralic Pennsylvanian (upper Carboniferous) successions crop out in the Subvariscan Basin between Aachen and Osnabruck, and continue into the subsurface of Northern Germany. Intramontane successions, with few exceptions starting in the Pennsylvanian, occur in several, in part extended basins in southwestern and central Germany. They are known from outcrop and subsurface. The diversified facies of the Carboniferous in Germany is controlled by the northwestern progradation of the Variscan Orogeny and its finalisation during the late Westphalian. During the Mississippian, megafacies realms include deeper water basinal sediments and flysch deposits, and laterally adjoining shallow-water platform carbonates (Kulm facies and Carboniferous Limestone facies, respectively). Locally starting in the later Mississippian (upper Visean), paralic and purely continental intramontane molasse deposits prevail during the Pennsylvanian. The traditional lithostratigraphic terms of the Mississippian regional standard profiles of Aachen and the western and northern Rhenish Mountains (Velbert, Sauerland) were completely substituted by new formations. Lithostratigraphic terms of the northeastern and eastern Rhenish Mountains (Kellerwald, Lahn-Dill area) were completely revised, as provenance analyses of detrital zircons enabled the differentiation of Rhenohercynian and Armorican nappes. Also the Mississippian of the Thuringisch-Frankisches Schiefergebirge and the Frankenwald (Franconian Forest) are better differentiated; formations were introduced for most lithostratigraphic units. Minor modifications concern the Namurian of the Subvariscan Basin at the northwestern border of the Rhenish Mountains and the intramontane Pennsylvanian successions of several basins in central Germany