Publisher © Czech Geological Survey, ISSN: 2336-5757 (online), 0514-8057 (print)
Dyke swarms of ultrapotassic melasyenite to melagranite porphyries from the Central Bohemian Plutonic Complex and the Šumava part of the Moldanubicum
Abstract
Numerous dykes of melasyenite, quartz melasyenite and melagranite porphyries sometimes accompanied by minettes are typical for prevailing parts of the Central Bohemian Plutonic Complex (CBPC) of Variscan age and for a large part of the Šumava Moldanubicum S of CBPC. Their chemistry, contrasting with common granitoids, corresponds to ultrapotassic silica-saturated plutonic rocks cropping out in E part of CBPC. All these rocks are rich in MgO (> 3 wt%), Cr (commonly > 200 ppm), K2O (6 to 7 wt%) and many mantle-incompatible elements, namely Cs, Rb, Pb, Th, U. Their parental mafic magmas originated within anomalous domains of lithospheric mantle metasomatized with upper-crustal material. Melagranite porphyries are chemically identical with durbachitic melagranites, i.e. the "light facies" of the Čertovo břemeno type, and show petrographic features of hybrid rocks originated by magma mixing. The quartz melasyenite porphyries are very similar to the most SiO2-rich varieties of the Tábor syenitoids and lack any unequivocal petrographic criteria for their hybrid .
