KINEMATICS OF A MAJOR FAN-LIKE STRUCTURE IN THE EASTERN PART OF THE SVECONORWEGIAN OROGEN, BALTIC SHIELD, SOUTH-CENTRAL SWEDEN

The N-S-trending so-called Protogine Zone in the Baltic Shield of sout h-central Sweden is usually considered to mark a tectonic boundary bet ween the rocks of the Transscandinavian Igneous Belt (TIB) in the east and the Sveconorwegian orogen in the west. Detailed structural mappin g in the Karlskoga-Kristinehamn area has shown that an anastomosing ne twork of ductile deformation zones with generally N-S strike extends c a. 40 km east of the traditional ''Protogine Zone''. Furthermore, the: western boundary of this ductile deformation and the TIB is not constr ained in the Kristinehamn area. Reconnaissance studies indicate that t hey both extend westwards towards the so-called Mylonite Zone. It is s uggested that the eastern limit of the Sveconorwegian orogen is locate d some 40 km east of the present boundary and that the ''Protogine Zon e'' concept is obsolete. The term Sveconorwegian Frontal Deformation Z one (SFDZ) is proposed as a more appropriate alternative in southern S weden (south of lake Vattern) and to correspond to a younger set of ob lique ductile deformation zones with reverse and right-lateral compone nts of movement in the easternmost part of the orogen farther to the n orth. Ductile deformation zones older than the SFDZ in the Karlskoga-K ristinehamn area display a fan-like geometry in an E-W cross-section, with steep westerly dips in the eastern part of the section, Vertical dips farther west and moderate easterly dips in the western part of th e section. Kinematic analysis indicates that dip-slip movements predom inate with a consistent top-to-the-east sense of movement across the e ntire fan-like structure. In their present orientation, deformation zo nes are characterized by reverse movements in the eastern part and nor mal movements in the western part of the structure. Between Kristineha mn and the Mylonite Zone, the main foliation is gently dipping to subh orizontal, indicating that the regional structure is strongly asymmetr ic, and that the fan-like structure occurs close to the foreland of th e orogen. Deformation zones are spaced to semi-penetrative in the east ern part of the fan-like structure, whereas the deformation is more or less penetrative and the TIB rocks are transformed to orthogneisses w est of Kristinehamn: This east to west increase in bulk strain is in a ccordance with an increase in syn-deformational metamorphic grade acro ss the structure. Younger ductile deformation zones belonging to the S FDZ are responsible for a major change in orientation of the older def ormation zones in the easternmost part of the structure. The fan-like structure is best explained by models involving the interference of tw o separate tectonic events. Deformation occurred after similar to 1.57 Ga and prior to deposition of Neoproterozoic and younger cover sedime ntary rocks. It is not yet clear whether the initial phase of deformat ion (early Sveconorwegian or older) was related to the build-up of an imbricate thrust stack in a compressional regime, as favoured here, or to regional E-W extension. The younger deformation phase was related to rotation of these older structures into the compressional, late Sve conorwegian SFDZ.