The Bohemian Massif (Hercynian Europe) is characterized, by the presence of high-P (depths of 50km) low-T granulites in Moldanubian and Saxothuringian units. Granulites underwent different degrees of progressive and retrogressive metamorphism along similar PT-t paths.
The "crustal" xenoliths present in Tertiary volcanic rocks in North Bohemia (Ohre-Eger rift) and isolated occurences of basalts in western Bohemia contain granulite (charnockite) parageneses (Vrána and Opletal, 1985). The charnockite xenoliths contrary to Moldanubian and Saxothuringian granulite massifs appear to have suffered high-T. Similarly to charnockites the gabbroic rocks that occur as xenoliths in basalts indicate relatively low-P and high-T of last "complete" equilibria. The gabbroes are apparently high-T cummulates. Contrasting PT conditions of formation could be shown in the upper mantle rocks that
were emplaced into Moldanubian metamorphic sequences (high P) and those occuring as xenoliths in basalts (high T). The differences still exist within the North Bohemian high-T occurences and Ulrych et al., 1996 have suggested that ultramafic and ultra-alkaline lavas of Cretaceous Tertiary volcanism of Ohøe (Eger) area are older i.e., 79-50 Ma and pre-date rifting and occur in the external blocks of Ohøe rift, whereas younger i.e., 40 - 24 Ma volcanic rocks are bimodal (basanite - fonolite), have a alkaline character and occur in the Ohøe rift.
We note that ultramafic and mafic volcanic rocks contain gabbro xenoliths, whereas charnockites occur in the bimodal series. Both series i.e., charnockitic and gabbroic xenoliths have similar PT-t paths characterized by the high -T.
The geochemistry of low and high pressure granulites shows principal differences in LIL and REE. The absence of gabbro cummulates in southern Bohemia and their presence in north Bohemia associated with charnockites suggest differences in PT evolution of granulites and upper mantle rocks.
Different orientations of mantle anisotopy and contrasting petrology and geochemistry of lower crustal and upper mantle rocks suggest the presence of different lithospheric lithologies in northern and southern parts of Bohemian massif. Though we are aware of the fact that we compare lithospheric sections that are of different age of closing temperatures (North Bohemian lithospheric section is much younger) we believe that the contrasting lithospheric sections result from different processes and may represent the Gondwana lithosphere (south), and Baltica (north)