TSK 11 Göttingen 2006 Klimczak & Riller
 Deformation of the Onaping
 Formation in the NE-lobe of
 the Sudbury Igneous Com-
 plex, Canada: Evidence for
 fold adjustment flow in the
 core of a km-scale foldPoster
 Christian Klimczak1 Ulrich Riller2
 The synformal geometry of the 1.85Ga
 Sudbury Igneous Complex (SIC), an im-
 pact melt sheet resulting from large-
 magnitude meteorite impact, attests to
 post-impact deformation. However, in
 contrast to the overlying Onaping For-
 mation, a heterolithic impact melt brec-
 cia, the SIC shows little evidence for
 pervasive ductile strain. This pertains
 in particular to its NE-lobe character-
 ized by a curvature of about 100° in
 plain view. This curvature has been in-
 terpreted either as a fold or as a primary
 feature. In order to test these scenarios,
 a detailed structural analysis was con-
 ducted in the core of the NE-lobe, which
 consists of rocks of the Onaping Forma-
 tion.
 Structural measurements and litholog-
 ical observations made at a total of
 700 stations collectively led to the con-
 struction of a detailed structural map of
 the Onaping Formation in the NE-lobe.
 The map displays a non-systematic fold
 pattern evident by individual units of
 the Onaping Formation, which from
 bottom to top are known as the Basal,
 the Grey, the Green and the Black Mem-
 bers. The fold pattern of these units
 is characterized by elongate domes and
 basins, the axes of which trend ap-
 proximately NE–SW. These axes are
 1 Freie Universität Berlin, Institut für Ge-
 ologische Wissenschaften, Malteser Strasse
 74-100, D-12249 Berlin 2 Humboldt-Univer-
 sität Berlin, Institut für Mineralogie, Invaliden-
 strasse 43, 10115 Berlin
 collinear to the uniformly SW-dipping
 planar mineral shape fabrics suggesting
 that the formation of these fabrics is ge-
 netically related to that of the domes
 and the basins. Near km-scale struc-
 tural discontinuities, which in the field
 and digital elevation models are evident
 by their strong gradients in topography,
 the strike of the mineral fabrics gener-
 ally matches that of the discontinuities.
 In terms of scale and structures devel-
 oped, deformation of the Onaping For-
 mation in the core of the NE-lobe is,
 therefore, highly heterogeneous.
 Based chiefly on the shape-preferred
 alignment of metamorphic minerals, the
 intensity of shape fabrics was visually
 estimated. Fabric intensity is strongest
 at the top of the Onaping Formation but
 decreases dramatically towards its con-
 tact with the SIC. This intensity gradi-
 ent corresponds well with the size of ma-
 trix minerals as well as with granitoid
 and metasedimentary fragments, which
 increases toward the base of the Onap-
 ing Formation. Apart from this litholog-
 ically controlled correspondence, shape
 fabric intensity is maximal in the cen-
 tral portion of the NE-lobe and, along
 with the axial-planar geometry of the
 planar mineral fabrics, attest to gener-
 ation of the NE-lobe be folding of the
 SIC around a south-westerly plunging
 axis. During such folding, deformation
 of the mechanically less competent On-
 aping Formation was accomplished het-
 erogeneously, evident by the highly vari-
 able fold geometry and shape fabric in-
 tensity. Such heterogeneous deforma-
 tion is typical for fold-adjustment rock
 flow in fold hinge zones of mechanically
 more competent rocks, i.e., the SIC.
 1