Publisher © Czech Geological Survey, ISSN: 2336-5757 (online), 0514-8057 (print)
Occurrence of minerals with pre-Variscan shock metamorphosis in granite of Melechov granite body
AbstractThe metamorphic restite in the autochthonous Lipnice-and Kouty granites (the Melechov granite body, Moldanubian batholith, Bohemian Massif) contains some records of shock metamorphism. These include mainly planar deformation of ilmenite and apatite. The lack of significant post-Variscan deformation in the rocks shows that the impact event occurred prior to Variscan granitization, which deleted other impact textures, if they haven't been deleted earlier. Unexplained planar intergrowths of quartz and unaltered biotite, alternating on very fine (several micrometers) scale, were observed in the Lipnice granite. Their connection to the impact is not sure, however. The abundance of shock-deformed ilmenite at various localities of the granites and no signs of exogenous transport of the ilmenite exclude the possibility that this ilmenite could be a local contamination. Also the chemical compositions of deformed ilmenite and apatite are comparable to composition of these minerals (undeformed) in granites. The specification of both time and spatial extent of the impact event requires detailed investigation tracing the pre-Variscan history in the northern Moldanubian area, and thus it is rather at the beginning now.