Multistage metamorphism and deformation in high-pressure metabasites of the northern Adula Nappe Complex (Central Alps, Switzerland)

Metabasites from the northern Adula Nappe Complex (ANC) display a complex microstructural evolution recording episodes of deformation and metamorphic re-equilibration that were obliterated in the surrounding phengite-bearing schists. Pre-DI and DI deformation episodes are preserved as mineral inclusions within garnet cores of some amphibole-bearing eclogites and record high-temperature greenschist-/amphibolite-facies conditions. D2 produced an eclogite-facies foliation which developed at 580 +/- 70 degrees C and 19 +/- 3 kbar. D3 was a composite deformation episode which can be divided into three sub-episodes D3m, D3a and D3b which occurred as the metamorphism evolved from post-eclogitic high-pressure and low-temperature conditions through to amphibolite-facies conditions at 590 +/- 30 degrees C and 11.7 +/- 1.3 kbar. The D3 deformation episode was responsible for the development of the S3 regional-scale foliation in the surrounding schists, whilst D4 caused the development of an S4 greenschist foliation. The composite nature of the D3 episode indicates that rocks of the northern ANC experienced a protracted post-eclogitic structural reworking and that the current structure of this part of the Alps is a late-Alpine feature. Copyright (C) 2010 John Wiley & Sons, Ltd.