HR: 14:30h
AN: G23C-05    [Abstracts]
TI: Using a geodetic strain rate model for western North America to improve our understanding of the driving forces behind Basin and Range extension
AU: * Kreemer, C
EM: kreemer@unr.edu
AF: Nevada Geodetic Laboratory, Nevada Bureau of Mines and Geology, University of Nevada, MS 178, Reno, NV 89557 United States
AU: Hammond, W C
EM: whammond@unr.edu
AF: Nevada Geodetic Laboratory, Nevada Bureau of Mines and Geology, University of Nevada, MS 178, Reno, NV 89557 United States
AB: The past and present-day extensional deformation fields in the northern Basin and Range (BR) Province have variably been explained to be the result of a variety of geodynamic forces. Particularly, stresses resulting from gravitational potential energy (GPE) differences (due to lithospheric and/or asthenospheric density variations) have been invoked in many studies to explain all or most of the extensional deformation. An alternative hypothesis is that BR extension could be explained on purely kinematic grounds; i.e., as a result of the Pacific plate pulling away from the Colorado Plateau. To separate the two mechanisms, areas of extension and contraction (ie, kinematic `sources' and `sinks') need to be recognized and compared to GPE gradients. The relative Pacific-North America (PA-NA) motion implies a transform plate boundary zone between the two plates, as is evident along the Queen Charlotte and southern Imperial Valley Faults in the north and south, respectively. Between these faults lies a part of the plate boundary zone, including the BR, that is much wider and more complex. Yet, when Juan de Fuca (JdF) motion is accounted for as a rotating block within the PA-NA boundary, the crustal flow field within the diffuse plate boundary zone must satisfy the condition of being part of a transform plate boundary zone. That is, the net-flux of material in or out the plate boundary zone is expected to be zero. When we apply Gauss' Theorem to a strain rate field derived from geodetic velocities and imposed JdF motion, we show that there is indeed no net-flux; i.e., the net-dilatation within the boundary zero is zero. The constraint of no net-dilatation allows us to compare BR extension with zones of contraction within the plate boundary zone, as indicated by the strain rate model. If the relative position of the identified source and sink are not consistent with GPE gradients, the present-day BR extension is probably of kinematic origin. A correlation, on the other hand, would be consistent with (but not necessarily proof of) a causal relationship between GPE gradients and extension.
UR: http://geodesy.unr.edu
DE: 1206 Crustal movements--interplate (8155)
DE: 8109 Continental tectonics--extensional (0905)
DE: 8123 Dynamics, seismotectonics
SC: Geodesy [G]
MN: 2005 Joint Assembly