LATERALLY CONSTRICTED SHEAR ZONE SYSTEM - THE NORDRE STROMFJORD STEEPBELT, NAGSSUGTOQIDIAN OROGEN, W GREENLAND

Many ductile shear zones are interpreted to operate by simple shear fl aw but some form under other flow regimes. Lineations and foliations i n such shear zones can lie obliquely to those in simple shear zones, w hich can lead to erroneous tectonic interpretations on the assumption of simple shear flow. This paper describes a gently dipping shear zone system from the N-central segment of the Palaeoproterozoic Nagssugtoq idian orogen of W. Greenland, which operated with a lateral constricti on component. This resulted in the development of upright folds with a xes parallel to the transport direction where the constriction compone nt is weak. Where it is strong, a linear fabric and even a subvertical foliation normal to the rotation axis of bulk flow developed. This st eep foliation is interpreted as the origin of the Nordre Stromfjord st eep belt, previously interpreted as a crustal-scale sinistral transcur rent shear zone. Shear zones of this type may occur elsewhere and shea r zone fabrics should therefore be carefully analysed before the direc tion of tectonic transpost can be determined.