The Brno Batholith: an insight into the magmatic and metamorphic evolution of the Cadomian Brunovistulian Unit, eastern margin of the Bohemian Massif

Abstract

The Brno Batholith, a part of the larger Brunovistulian Unit, consists of three genetically independent complexes, Western Granitoid Complex (part of the Thaya Terrane), Ophiolite Belt (formerly Metabasite Zone or Central Basic Belt), and Eastern Granitoid Complex (part of the Slavkov Terrane). The field with geochronological evidence indicate younger age of both granitoid complexes compared with the ophiolite. The composition of the Eastern Granitoid Complex (not newly studied in this paper) points to a relatively primitive Cadomian volcanic-arc environment. The Ophiolite Belt comprises a tilted segment of an almost complete metamorphosed ophiolite sequence with lithologically and geochemically obvious suprasubduction signature. Three main granite suites, with distinct S, I, and A type affinities, are exposed in the Western Granitoid Complex. Abundance of crustal xenoliths, complex morphological zircon population, overall S type chemistry, as well as geophysical and petrological evidence for basalt underplating, all point to the origin of the Tetcice suite via melting of the older metasedimentary crust. The Rena suite consists of I type volcanic-arc granodiorites to granites, whereas small intrusions of granites with certain A type affinity are characteristic of the Hlina suite. Equivalents of all three suits were recognized in the northern part of the Dyje Batholith, which represents the direct continuation of the western branch of the Brno Batholith. The geological structure and geochronological data from both the Brno and Dyje batholiths exhibit some similarities with those documented in the Eastern Desert in Egypt. This may indicate a probable Gondwana affinity to the whole Brunovistulian assembly.