HR: 14:55h
AN: S22C-06 INVITED     [PDF]
TI: Flexural Strength Of Continental Lithosphere: What? Again? Don't We Know All About This Already?
AU: * Karner, G D
EM: garry@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, P.O. Box 1000, Palisades, NY 10964 United States
AB: A major controversy continues to exist concerning the flexural strength of the continental lithosphere despite 20+ years of active research on the subject. Lithospheric strength is often expressed as an effective elastic thickness (Te), an enginnering concept that relates the flexure of a thin elastic plate overlying a fluid substrate to its thickness. Te is used to represent the flexural strength and mechanical behavior of the lithosphere in a depth-averaged sense. Attempts to constrain Te accurately are commonly thwarted by an inadequate knowledge of load distribution (either surface or subsurface), lateral variations in Te, or appropriate geological and geophysical constraints. Two approaches are used to map the flexural strength of the lithosphere: 1) Inverse gravity admittance and coherence techniques, which exploit the statistical relationship between topography and gravity anomalies; and 2) Forward modeling strategies that attempt to model the architecture of extensional and foreland basins and their respective free-air gravity anomalies. In the latter, load amplitude and distribution are constrained by sediment thickness, stratal relationships, and the geological and tectonic history of the basin. In the former, large 2D and often significantly incomplete data sets are Fourier transformed and used with approximations for surface and subsurface loading ratios to map Te. Forward modeling of simple loading systems (e.g. rift flank topography and foreland basin architecture) and the flexural response to serendipitous surface loads (e.g. Kilimanjaro and Mt. Erebus) is probably the most reliable approach to estimate Te. The long-term temporal behavior of Te is provided by analyses using the wavelength and amplitude of free-air gravity anomalies observed in many cratons (e.g. central Australia and Brazil) and the geometry of Proterozoic foreland basins. The present failure to find a straightforward relationship between Te and the thermal structure of the continental lithosphere is likely a consequence of an incomplete, if not compromised, database of continental Te values. Research needs to concentrate on improving considerably the quality of Te estimates before statements of weak continental mantle, relationships between Te and seismogenic zone thickness, and the rheological zonation of the lithosphere can be assessed reliably.
DE: 7299 General or miscellaneous
DE: 8105 Continental margins and sedimentary basins
DE: 8110 Continental tectonics--general (0905)
DE: 8122 Dynamics, gravity and tectonics
DE: 8160 Rheology--general
SC: Seismology [S]
MN: 2003 Fall Meeting