HR: 12:00h
AN: U52A-06    [Abstracts]
TI: Horizontal Thermal Contraction of Oceanic Lithosphere and Implications for the Rigid Plate Approximation
AU: * Kumar, R
EM: rkumar@rice.edu
AF: Rice University, Earth Science--MS 126 6100 Main Street, Houston, TX 77025 United States
AU: Gordon, R G
EM: rgg@rice.edu
AF: Rice University, Earth Science--MS 126 6100 Main Street, Houston, TX 77025 United States
AB: It is well accepted that predictable thermal contraction accounts for the subsidence of oceanic lithosphere with age. The same models imply horizontal contraction of the lithosphere as well. The total cooling of the seismogenic upper oceanic lithosphere is about 10³ Kelvin. A linear coefficient of thermal expansion of about 10^-5 implies a contraction of about 1%. For a global plate motion circuit (e.g., Pacific to Antarctic to Nubia to North America), this indicates a potential bias of up as much as several hundred kilometers, an order of magnitude larger than the formal errors on some published estimates. The contraction is largely concentrated in young lithosphere. Simple models indicate that the average rate of contraction for lithosphere during its first 10 Myr of existence is on the order of 0.1%/Myr. It is convenient to separate the horizontal contraction into two components---one parallel and one perpendicular---to the direction of relative plate motion. The effect of the former implies a simple correction to the angular velocity, which causes plate motion estimated from marine magnetic anomalies to be upward biased by about 1%, an effect which may eventually be detectable in comparisons with space geodetic data. The effect of the latter is more complex and depends on the details of plate geometry and plate motion circuits. Insofar as the contraction is symmetrical, there may be no bias introduced to plate motions estimated across a mid-ocean ridge. The effect may be very large in global plate motion circuits, however, with biases possibly as large as ~10 mm/year.
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8149 Planetary tectonics (5475)
DE: 8155 Plate motions: general (3040)
SC: Union [U]
MN: Fall Meeting 2005