Czech eclogites; terrane settings and implications for Variscan tectonic evolution of the Bohemian Massif

Eclogite and peridotite of different types and ages occur in different terranes in the Czech part of the Bohemian Massif: the Tepla, Monotonous and Varied, and Gfohl terranes. 1) Tepla terrane: prograde eclogite occurs in metabasite units of the Marianske Lazne metaophiolite. Minimum TP conditions are 625 degrees -730 degrees C, 13.7-16.4 kbar. Spinel peridotite in the complex is recrystallized to tremolite schist and serpentinite. Eclogite formed as a result of B-type subduction related to Devonian closure of a Saxothuringian ocean. 2) Monotonous and Varied terrane: prograde eclogite occurs as lenses and boudins in gneiss and in serpentinized spinel peridotite. Minimum TP conditions are 615 degrees -705 degrees C, 13.4-15.1 kbar. This eclogite group probably formed from basaltic protoliths during continental collision and imbrication, but the age of this event remains undetermined. 3) Gfohl terrane: retrograde eclogite occurs as lenses or layers in garnet peridotite in Gfohl gneiss, but is rare in granulite. Minimum TP conditions are 765 degrees -1190 degrees C, 12.4-19.8 kbar. These eclogites formed by high-pressure crystal accumulation of garnet and clinopyroxene. High-temperature garnet and spinel peridotites occur in Gfohl gneiss and granulite. The Gfohl assemblage may have originated as a Devonian volcanic arc and associated back-arc basin that was telescoped and imbricated during Carboniferous collision of Gondwana and Laurasia. Rapid exhumation, perhaps due to extensional collapse, must have closely followed the collisional event in order to preserve the high-temperature characteristics of Gfohl peridotites and eclogites.