HR: 16:00h
AN: T52F-01    [PDF]
TI: The Angular Velocity of Nubia Relative to Somalia and the Location of the Nubia-Somalia-Antarctica Triple Junction
AU: Horner-Johnson, B C
AF: Department of Earth Science, Rice University, Houston, TX 77005 United States
AU: * Gordon, R G
EM: rgg@rice.edu
AF: Department of Earth Science, Rice University, Houston, TX 77005 United States
AU: Cowles, S M
AF: Department of Earth Science, Rice University, Houston, TX 77005 United States
AU: Argus, D F
AF: Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 United States
AB: A new analysis of geologically current plate motion across the Southwest Indian Ridge and of the current location of the Nubia-Antarctica-Somalia triple junction is presented. We estimate spreading rates averaged over the past 3.2 Myr from 103 well-distributed, nearly ridge-perpendicular profiles crossing the Southwest Indian Ridge. We evaluate all available bathymetric data to estimate the azimuths and uncertainties of transform faults; six are estimated from multi-beam data and twelve from precision depth recorder data. If the Nubia-Somalia boundary is narrow where it intersects the Southwest Indian Ridge, that intersection lies between about $26\deg$ E and $32\deg$ E. This places it either along the spreading ridge segment just west of the Andrew Bain transform fault complex or along the transform fault complex itself. These limits are narrower than, and contained within, limits of about $24\deg$ E to $33\deg$ E previously found by Lemaux et al. (2002) from an analysis of the locations of magnetic anomaly 5. The data are consistent with a narrow boundary, but also consistent with a diffuse boundary as wide as about 700 km. The new Nubia-Somalia pole of rotation lies southwest of southern Africa and differs significantly from previously estimated poles, including that from data in the Red Sea and Gulf of Aden. The new pole indicates displacement rates of Somalia relative to Nubia of $3.4 \pm 1.3$\ mm\,yr$^{-1}$ (95% confidence limits) towards $176.8\deg$ between Somalia and Nubia near the Southwest Indian Ridge, and of $8.4 \pm 1.3$\ mm\,yr$^{-1}$ (95% confidence limits) towards $118.5\deg$ near Afar.
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 8158 Plate motions--present and recent (3040)
SC: Tectonophysics [T]
MN: 2003 Fall Meeting