Geochemistry of the Görcsöny Ridge amphibolites ( Tisza Unit , SW Hungary ) and its geodynamic

The Görcsöny Ridge is part of the complicated Variscan metamorphic basement of the SW Tisza plate. It was penetrated by several wells, one of which (Baksa-2) has 1200 m of well core available for petrological examination. Amphibolite samples of this core are of two different sorts: the fi rst group contains biot ite, rutile, and garnet, while the second group contains ilmenite and is free of garnet. The two rock types occur separately in the borehole, defi ning a lower and an upper unit (LU, UU). Based on their major and trace element compositions, LU samples represent within-plate (WP) tholeiites which assimilated pelagic sediments, while those of the UU represent WP alkali basalts. Thermobarometric calculations suggest that the difference in chemical composition itself does not explain the above differences in mineralogy, so the two units must also differ in their metamorphic histories. Consequently, the crystalline basement of the Görcsöny Ridge possibly consists of amalgamated fragments of different origins which became juxtaposed during the variscan collisional orogeny.