Seismic observations along the European Geotraverse (EGT) Central Segment indicate an overall felsic composition of the Variscan crust, including 15 vol. % of mafic lower-crustal (MLC) rocks. As the Variscan continental crust is largely post-Archaean, its bulk composition should be basaltic andesitic rather than felsic (tonalitic), because primitive post-Archaean crust was formed by mantle extracted basaltic andesite magmas. The observed proportions of the Variscan continental crustal layers do not match the requirement of a mafic overall crust. Combining laboratory-derived, in situ seismic data (VP) with the refraction seismic data and the evidence from geological and geochemical investigations suggests that large amounts of MLC rocks are missing in the present-day lower crust. A mass balance calculation of the basaltic andesite bulk crust, considering a refined compilation of the Variscan MLC, gives a volume proportion of 37 vol. % for the felsic and 63 vol. % for the mafic components, for primitive crust prior to collision tectonics and orogenic root delamination. If large parts of this MLC have undergone eclogite-facies metamorphism at the orogenic root, large amounts of former basaltic-gabbroic and MLC cumulates could have been subtracted from the crust by its subsequent delamination processes which results in the currently observed proportion of the continental crust of the Variscan Orogen with a predominance of felsic rocks.
This editorial reports on a thorough analysis of the abundance and scarcity distribution of chemical elements and the minerals they form in the Earth, Sun, and Universe in connection with their number of neutrons and binding energy per nucleon. On one hand, understanding the elements’ formation and their specific properties related to their electronic and nucleonic structure may lead to understanding whether future solutions to replace certain elements or materials for specific technical applications are realistic. On the other hand, finding solutions to the critical availability of some of these elements is an urgent need. Even the analysis of the availability of scarce minerals from European Union sources leads to the suggestion that a wide-ranging approach is essential. These two fundamental assumptions represent also the logical approach that led the European Commission to ask for a multi-disciplinary effort from the scientific community to tackle the challenge of Critical Raw Materials. This editorial is also the story of one of the first fulcrum around which a wide network of material scientists gathered thanks to the support of the funding organization for research and innovation networks, COST (European Cooperation in Science and Technology).
The major share of raw materials needed to sustain our present lifestyle and even more importantly, required for the crucial green transition, are sourced outside Europe. The European Commission aims to enhance Europe's resilience and strengthen domestic sourcing. Although Europe has a long tradition of mining and extractive activities, it is acknowledged that there are several challenges to achieve European sourcing of certain raw materials such as the critical raw materials. A basic prerequisite to enable access to domestic raw materials is information on raw material occurrences, current and past mining activities, resources and reserves. The Geological Survey Organisations (GSOs) of Europe play a key role in generating, compiling, gathering, and storing the most up to date information as well as long-term data series on raw materials at national and regional levels. Over the last decade, the GSOs have joined forces and taken essential steps to harmonise and share data on raw materials. The results of this cooperation are illustrated as interactive maps on the European Geological Data Infrastructure (EGDI). This paper describes the data compiled in cooperation between the GSOs, and analyses the strengths and weaknesses of as well as opportunities for and threats towards the data.
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