Pre-Mesozoic lamprophyres and associated dyke intrusions of the Bohemian Massif (Czech Republic, Poland, Germany, Austria): a reviewArticle PDF
Pre-Mesozoic lamprophyres and associated dyke intrusions of the Bohemian Massif (Czech Republic, Poland, Germany, Austria): a review
This contribution summarizes and comments the most important published results on pre-Mesozoic lamprophyres of the Moravo-Silesian, Moldanubian, Kutná Hora-Svratka, Central Bohemian, Saxothuringian and Lusatian Region.
The contribution also brings a current view on a definition and nomenclature of lamprophyres. After more then one hundred years growing the family of lampropfyric rocks, we can now restore the Rosenbuch’s initial concept based only on five principal lamprophyre types: minette, kersantite, spessartite, vogesite and camptonite. Due to the differentiation processes (e.g. magma mixing, fractional crystallization), the lamprophyres are often accompanied by contemporaneous dyke rocks petrographically ranging from microgabbro/microdiorite to microgranite.
Based on the new results of Ar-Ar step-heating dating, the majority of lamprophyres of the Bohemian Massif is late Variscan. The temporal range of lamprophyric magmatic activity is at least 60 Ma (334–274 Ma). Two peaks of lamprophyric magmatism occurred close to the Lower/Upper Carboniferous and Upper Carboniferous/Permian boundary. The youngest (uppermost Lower Permian) lamprophyre intrusive event. occurs in the eastern orogenic foreland in the Moravo-Silesian Region. Important demonstration of the Variscan mantle magmatic activity of lamprophyric composition is the occurrence of hybrid intrusions of durbachites (Moldanubicum) and redwitzites (Saxothuringicum). Mantle (lamprophyric) magmatism also played important role during the genesis of post-collisional granitic plutons at the NE margin of the Bohemian Massif, such as those of Krkonoše-Jizera, Strzegom-Sobótka, Kłodzko-Złoty Stok, Strzelin and Žulová.
Distribution of lamprophyres within the single regions of the Bohemian Massif is not uniform. They show distinct connection to important sutures and tectonic zones. Some minettes cropping out close to the Bohemicum/Moldanubicum boundary, or its presumed equivalent in Lugicum, show a negative Eu anomaly as a primary feature of contamination of their mantle source by subducted evolved continental crust. These minettes bring petrographic and geochemical characteristics gradational between typical lamprophyres and lamproites. Additionally, unique post-collisional potassium-rich dyke rocks characterized by mineral assemblage K-rich amphibole – microcline ± phlogopite ± aegirine ± quartz were encountered in the Moldanubian and in the Lasutian Region. The dykes have been originally described under local or incorrect names such as “raabsite” (“peralkaline minette”), “thuresite” (“peralkaline microsyenite”) and “karlsteinite” (“peralkaline microgranite”). Despite their previous petrogenetic classification as intrusions of the “minette differentiation series”, the dykes show mineralogical and geochemical features similar to SiO2-rich orogenic (postcollisional) lamproites of Mediterranean-type. Lamprophyres of the Saxothuringian Region are spatially and/or genetically connected with regionally important (indium-bearing) ore districts.
Lukáš Krmíček, Institute of Geological Sciences, Masaryk University, Brno, Kotlářská 2, 611 37 Brno, Czech Republic, email: email@example.com