DEFORMATION-INDUCED CLINOPYROXENE FABRICS FROM ECLOGITES

Clinopyroxene (omphacite) microfabric studies in eclogites are useful in characterizing the deformation that has affected deeper parts of subduction zones. We present the microfabrics and TEM structures of four samples representative of the various deformation types known in eclogites. The [001] axis tends to be parallel to the lineation while the (010) plane is close to the foliation, but these general features undergo strong variations in relation to the shape fabric: in strongly-lineated samples, [010] tends to be spread out in a great circle normal to the lineation, whereas [001] is dispersed in the foliation in the case of strongly-foliated samples. The slip systems identified by TEM are [001](100), [001]{110} and 1/2 < 110 >{($) over bar 110}. Operation of dislocation creep is testified by the presence of dislocations and dislocation walls, but this process alone cannot explain all the observed features, particularly some aspects of the crystallographic preferred orientation, hence other deformation mechanisms must be involved. These may be dynamic migration recrystallization by grain boundary migration, as well as mass transfer processes. This study illustrates that not every crystallographic mineral preferred orientation can be explained by dislocation glide and/or twinning processes alone. In addition, it also demonstrates that eclogite microfabrics can be used to unravel deformation parameters in subduction and/or collision zones.