TY - JOUR
T1 - Structure and origin of the Fleurieu and Nackara Arcs in the Adelaide fold-thrust belt, South Australia
T2 - Salient and recess development in the Delamerian Orogen
AU - Marshak, Stephen
AU - Flöttmann, T.
N1 - Funding Information:
Acknowledgemenfs-We are very grateful to Pat James for making this project possible and for his insightful suggestions at all stages of the project. We also wish to thank Tony Belperio, John Foden, Dick Glen, Alex Grady, David Gray, Bob Hatcher, Richard Hillis, Richard Jenkins, Nick Lemon, David Miller, Wolfgang Preiss, Mike Sandiford, Kurt Stiiwe, Rowlv Twidale, Rob Menpes, Martin Fairclough, Jerome Randabel, Pasquaie Cesare, and Mark Twining for helpful discussions, and Dick Glen. Vicki Hansen. Jerrv Manlouehlin. Dick Norris. Nick Woodward, Scott Wilkerson, and Tom Wright for criticism of earlier versions of the manuscript. We do not intend to imply that the colleagues listed above agree with all of our conclusions. Grants from the University of Illinois Research Board and the National Geographic Society (U.S.A) provided partial funding to S. Marshak, and a grant from the Australian Research Council to P.R. James provided partial funding to Flottmann. We carried out our field work while Marshak was on leave at the University of Adelaide.
PY - 1996/7
Y1 - 1996/7
N2 - The regional map pattern of structural trends in the Early Paleozoic Adelaide fold-thrust belt of South Australia resembles an upright letter 'S'. In general, structures in the fold-thrust belt verge toward the Gawler craton to the west, so the northern curve (Nackara Arc) of the 'S' is a salient, whereas the southern curve (Fleurieu Arc) is a recess. The map-view axial trace of the Nackara Arc coincides with the thickest portion of the Adelaidean (Late Proterozoic) basin, and the map-view axial trace of the Fleurieu Arc coincides with the intersection between the Adelaidean and Kanmantoo (Cambrian) basins. Our structural analysis of the Adelaide fold-thrust belt demonstrates that the cross-sectional structural geometry of the Nackara Arc contrasts markedly with that of the Fleurieu Arc. In the Nackara Arc, the belt consists of open detachment folds that probably formed above an evaporite-hosted décollement, whereas in the Fleurieu Arc, the belt consists of an imbricate fan of basement-involved thrusts. Further, the foreland edge of the Nackara Arc coincides with a blind ramp whose strike parallels fold axes of the arc, whereas the foreland edge of the Fleurieu Arc coincides with emergent thrusts that cut obliquely across earlier formed folds of the arc. In the transition region between the two arcs, the fold-thrust belt consists of an intensely sheared basal duplex overlain by open folds. Structural contrasts between the Nackara and Fleurieu Arcs indicate that the two curves did not form in the same way. We present a model for development of these curves based on a comparison of their structural features to those of curves in other fold-thrust belts, and based on previous studies of curve formation using sandbox analogs. We suggest that curvature of the Nackara Arc reflects the control of basin stratigraphy on the width of a fold-thrust belt, while curvature of the Fleurieu Arc reflects oroclinal bending of the fold-thrust belt when it impinged on the southeastern corner of the Gawler craton. Our model explains the structural contrast between the two arcs and illustrates correlations between fold-thrust belt curve formation and pre-deformational basin geometry.
AB - The regional map pattern of structural trends in the Early Paleozoic Adelaide fold-thrust belt of South Australia resembles an upright letter 'S'. In general, structures in the fold-thrust belt verge toward the Gawler craton to the west, so the northern curve (Nackara Arc) of the 'S' is a salient, whereas the southern curve (Fleurieu Arc) is a recess. The map-view axial trace of the Nackara Arc coincides with the thickest portion of the Adelaidean (Late Proterozoic) basin, and the map-view axial trace of the Fleurieu Arc coincides with the intersection between the Adelaidean and Kanmantoo (Cambrian) basins. Our structural analysis of the Adelaide fold-thrust belt demonstrates that the cross-sectional structural geometry of the Nackara Arc contrasts markedly with that of the Fleurieu Arc. In the Nackara Arc, the belt consists of open detachment folds that probably formed above an evaporite-hosted décollement, whereas in the Fleurieu Arc, the belt consists of an imbricate fan of basement-involved thrusts. Further, the foreland edge of the Nackara Arc coincides with a blind ramp whose strike parallels fold axes of the arc, whereas the foreland edge of the Fleurieu Arc coincides with emergent thrusts that cut obliquely across earlier formed folds of the arc. In the transition region between the two arcs, the fold-thrust belt consists of an intensely sheared basal duplex overlain by open folds. Structural contrasts between the Nackara and Fleurieu Arcs indicate that the two curves did not form in the same way. We present a model for development of these curves based on a comparison of their structural features to those of curves in other fold-thrust belts, and based on previous studies of curve formation using sandbox analogs. We suggest that curvature of the Nackara Arc reflects the control of basin stratigraphy on the width of a fold-thrust belt, while curvature of the Fleurieu Arc reflects oroclinal bending of the fold-thrust belt when it impinged on the southeastern corner of the Gawler craton. Our model explains the structural contrast between the two arcs and illustrates correlations between fold-thrust belt curve formation and pre-deformational basin geometry.
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U2 - 10.1016/0191-8141(96)00016-8
DO - 10.1016/0191-8141(96)00016-8
M3 - Article
AN - SCOPUS:0030185155
SN - 0191-8141
VL - 18
SP - 891
EP - 908
JO - Journal of Structural Geology
JF - Journal of Structural Geology
IS - 7
ER -