HR: 1340h
AN: U43B-0837    [Abstracts]
TI: Post-Rift Deformation of Passive Margins
AU: * Jackson, J S
EM: jackson.js@comcast.net
AF: Geology Department, Portland State University, P. O. Box 751, Portland, or 97206 United States
AB: A variety of post-rift deformations occur across basins on the passive margins of the Atlantic and Indian Oceans. These deformations are most pronounced in deep water settings, but are also observed in shallow water and onshore. The resulting structures range in scale from local uplift and inversion to regional exhumation. Small scale compression is observed on the margins of the North Atlantic Ocean, and on the Australian Northwest Shelf of the Indian Ocean. The effects include small scale doming and minor inversion of normal faults. These features occur near fracture zones and transform faults. The reorganization of sea floor spreading appears to be coeval with the development of these compressional features. Although ocean plates appear to behave as first-order, large-scale rigid plates, these observations suggest that fracture zones and transform faults subdivide ocean plates. The smaller plates deform in response appropriate ridge-push stresses. In the Equatorial Atlantic long transform faults offset the ocean crust, and appear to be intermittently active into the Holocene. Strike-slip deformation is inferred from positive and negative flower structures found on both the African and South American margins. Movement on the transform faults appears to result from minor changes in sea-floor spreading along the mid-ocean ridge. On a larger scale, Neogene regional doming is observed in Scandinavia and North America. These features do not appear related to changes in sea floor spreading. A wedge of sediments shed from these domes is found in the adjoining ocean basins. The base of these sediments appears to precede the onset of glaciation. Mantle flow is inferred to be downward beneath the older portions of the ocean basins, and/or upward beneath adjoining continental domes. These observations suggest that mantle upwelling processes continue to effect passive margins long after continental rifting and the onset of sea-floor spreading. It is well known that the rate of upwelling varies after rifting, as seen in ocean floor ages. The lateral flow of mantle away from the mid-ocean ridges is inferred to also vary, resulting in deformation seen on both oceanic and continental crust.
DE: 3039 Oceanic transform and fracture zone processes
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 9325 Atlantic Ocean
DE: 9340 Indian Ocean
SC: Union [U]
MN: Fall Meeting 2005