From Cadomian accretion to Variscan collision: a crustal-scale traverse across the northwestern Teplá–Barrandian unit
Abstract
The Teplá–Barrandian unit (TBU), occupying a central position in the Bohemian Massif, is a superbly exposed upper-crustal fragment of the Avalonian–Cadomian orogenic belt that constituted an active plate margin along the northern Gondwana during late Neoproterozoic to early Cambrian times. Despite later involved in a broad collision zone of the internal Variscan belt, the TBU, in contrast to adjacent units, largely escaped the pervasive Variscan reworking and metamorphism.
In the Barrandian syncline, located between Plzeň and Prague, unmetamorphosed Cambrian to Middle Devonian successions rest unconformably on top of Neoproterozoic metasedimentary and metavolcanic rocks. Degree of regional metamorphism generally increases in the Neoproterozoic rocks from the Barrandian syncline (prehnite-pumpellyite facies at most) to the W and NW (amphibolite facies).
Consequently, the TBU is a fascinating geologic archive tracing protracted, more than 300 m.y. long, tectonic history of two orogenies separated by an episode of rifting, basin development along a volcanic passive margin. During this time span, the TBU witnessed an impressive continental drift from a latitude of about 60° south at the northern margin of Gondwana in the late Neoproterozoic to its near-equator position during the final assembly of Pangea at the end of the Paleozoic Era.
The GEOPilsen 2013 pre-conference field trip will take us to a selection of most instructive outcrops in the northern and northwestern TBU that record the main events of this protracted tectonic history.