Hercynian deformation and metamorphism in the Cordillera Oriental of Southern Bolivia, Central Andes

In southern Bolivia the very thick Ordovician siliciclastic rocks of the Cordillera Oriental show folds and a slaty cleavage of pre-Cretaceous age. These deformations had previously been attributed to either the late Ordovician Ocloyic or to the late Devonian to early Carboniferous Eohercynian (Chanic) orogenies. Now, we present K/Ar age determinations from phyllosilicates of the Ordovician slates, which have been interpreted in relation to illite crystallinity data. High anchizonal to epizonal metamorphism is indicated for most of the investigated samples. The majority of the samples have provided ages within the 320-290 Ma interval (late Carboniferous to early Permian), indicating a late Hercynian orogeny. Traces of synchronous orogenic processes are known from different parts of the Central Andes. This points to late Hercynian orogenic activities in that region. (C) 2002 Elsevier Science B.V All rights reserved.