Pegmatitic Rocks and Their Geodynamic Setting in the Central European Variscides

Abstract

AbstractPegmatitic rocks are not randomly distributed across the Variscan/Hercynian basement in Central Europe. The evolution of pegmatites s.l. in the course of a complex orogeny of Meso-Europe took rather long, from the Devonian (419 Ma) through the Permian (252 Ma). In terms of structural geology and geodynamics, pegmatitic deposits primarily occur in ensialic Variscan-type orogens (calc-alkaline) with a thickened crust and a preponderance of thrusting and nappe stacking. In Rift-type settings (alkaline) a strong subcrustal impact is evident and as reactivated/reworked pseudopegmatites in Alpine-type orogens (calc-alkaline) these deposits developed during the initial stages when the crustal section was still rather thick. Both types pertain to the marginal ensimatic settings. They left their hallmarks to some extent also within the Central European Variscides and at its southern edge in the Alpine-Carpathian Orogen. The geodynamic units subjected to very-low-grade- to low-grade stage metamorphism at the margin of the Central European Variscides are barren with regard to pegmatites and aplites. Pegmatoids with minor B-(Li)-P-REE-U-Be mineralization occur along a suture zone extending across the present-day continents. It resulted from the late Variscan closure of the Rheic Ocean between Gondwana and Laurussia with remnants of an arc-related plutonism. Within allochthonous metamorphic complexes and nappes barren feldspar-quartz pegmatoids plus metapegmatites developed. Further south another part of this former coherent nappe also contains a small Be-Nb-P mineralization. Within the Subfluence zone, marked by continent-continent collision and thickening of the crust pegmatite, granite- pegmatite (miarolitic), pegmatite-aplite and pegmatoid abundant in B, Be, F, Li, Sn, U, P and As are encountered. Heading further to the core zone of the Variscan orogen, strong diapthoresis and shearing in the contact zone between the Saxothuringian and Moldanubian zones sensu lato favored the emplacement of pegmatite and aplite enriched in B, P, Be, Nb, As, Zr and F. High grade metamorphic rocks in an autochthonous position with a protolith mainly of Proterozoic age exist in the core zone. At the margin they are overthrusted onto adjacent geodynamic units and penetrated by multiple intrusions. The Hagendorf-Pleystein Pegmatite Province is located near the root zone for the nappe complexes thrusted onto the north-western geodynamic realms. Pegmatites and aplites with minor pegmatoids of the Hagendorf-Pleystein Pegmatite Province show the most varied concentration of rare elements in pegmatitic and aplitic rocks in this crustal section (B-P-REE-Nb/Ta-Li-Sc-Zn-Be). In some parts in core zone pegmatites can also be observed associated with skarns. Variscan lithologies were incorporated into the Alpine orogen and reactivated during the Alpine orogeny at the southern edge of the Meso-Europe. They contain granitic pegmatites, meta-pegmatites, pegmatoids and pseudo-pegmatites (B-Be-P-Nb-U-F-As-Li-Sn-REE-U). By quality this element assemblage is not very much different from that of the neighboring Variscan parent rocks. The suite of pegmatitic and aplitic mineral deposits is associated with mineral deposits of non-pegmatitic origin. They include thrustbound deposits (Au-As-Sb-(Hg)-Fe-Cu-Pb-Zn), plutonic/granite-related deposits (Sn-W-Mo-Pb-Ag-Zn-(In)-Cu-U), and unconformity-related (U-Pb-Zn-F-Ba). While the deposits can at least in parts structurally and compositionally related to the various types of pegmatites and aplites, stratabound deposits are mainly marker deposits for geodynamic units prone to aplitic or pegmatitic rocks in an ensialic orogen (SMS > > VM FeS-Cu-Zn, SEDEX Fe deposits, black-shale –hosted U-Cu-Mo-Sb-Zn-REE (low-grade-large-tonnage) and graphite). As an exception from this rule, the two last-mentioned mineralization with organic compounds can be considered (see geophysical surveys).KeywordsBohemian MassifGneiss ComplexRheic OceanMoldanubian ZoneRhenohercynian ZoneThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.