Back to list of UTIG abstract submissions, Fall Agu 2003

P. Mann, F.W. Taylor, L. Lavier, and H. Van Avendonk, Institute for Geophysics, University of Texas at Austin, Austin, TX 87859-8500 (paulm@ig.utexas.edu)

The Owen Stanley fault system (OSFS) is a regional, normal to transpressive plate boundary fault zone that traverses the entire 600 km length of the Papuan Peninsula and has controlled the location and Plio-Pleistocene uplift history of metamorphic core complexes (MCC’s) in the Dayman-Suckling massif and on the D’Entrecasteaux Islands. Near the eastern end of the peninsula, the Gwoira fault zone of the OSFZ is well exposed as an exhumed, striated, concave-downward normal fault surface across the Dayman-Suckling MCC. The Gwoira fault plane dips north at an angle of 14º; megastriations on the fault plane indicate dipslip displacement; earthquake focal mechanisms constrain active, north-south dipslip extension; GPS measurements constrain extension rates of 19 mm/yr. Pliocene-age marine sedimentary rocks entrained as a coherent, 170 km2 sheet on the fault plane constrain its post-Pliocene dipslip motion. The 25-32 km length of the exhumed Gwoira fault plane exposed across the Dayman-Suckling MCC provides a minimum estimate for offset along the normal fault. The footwall block is characterized by high topography up to 2-4 km at the crest of the Papuan Peninsula, Holocene coral reefs uplifted at rates of 4.3 mm/yr, and flights of terraces along deeply incised river valleys. The hanging wall block is occupied by a low relief coastal plain and a half-graben structure underlying Goodenough Bay (water depth: 1 km; 1.2 km of Miocene-recent sedimentary fill). In order to understand the relationship between this fault and now subsiding MCC’s located 80 km north of the Gwoira fault zone in the D’Entrecasteaux Islands, we present three numerical models that simulate three possible physical processes previously proposed for this area or for analogous areas: 1) extension controlled and focussed by crustal diapirism of a lower density and viscous lower crust; modeling predicts a crustal diapir ascending from a mid-crustal, low density layer; 2) mantle exhumation is controlled by a lithosphere-penetrating rolling hinge; modeling predicts an asymmetrical rolling hinge at a concave-upward normal fault after 10’s of kms of low-angle fault offset; and 3) extension is dominated by active mantle upwelling.