Abstract Title: The role of lateral heat conduction in continental extensional 
tectonics.

Abstract Author(s):   Harry, Dennis (Colorado State)

Abstract: Geodynamic models of extension in the Great Basin and West Antarctica 
show that tradeoffs between extension rate, dynamically evolving thermal 
conditions, and inititial conditions (structural fabrics, crustal heat 
production, and lithosphere and asthenosphere thicknesses) play a major role in 
determining the evolution of extensional provinces. Both of these are unusually 
wide regions of diffuse extension. In the Great Basin, extension began in a 
central region and spread outward with time. In West Antarctic extension was 
initially distributed over a broad region and became more focused with time. 
Geodynamic models indicate that the difference is due to a complex interaction 
between extension rates and initial lithospheric structure and thermal state. 
Slow extension promotes conductive cooling of the lithosphere, resulting in an 
increase in strength and a shift of extensional deformation to other regions 
(e.g., the Great Basin). Juxtaposition of two very different lithospheric 
terrains in Antarctica appears to have interrupted this process, resulting in 
late stage lithospheric necking near the East Antarctica-West Antarctica 
boundary. Extremely diffuse extension such as that seen in the Great Basin and 
West Antarctica, although not common, can be re-produced in the geodynamic 
models under a wide variety of conditions if the crust is sufficiently thick 
and the extension rate sufficiently slow. Extremely diffuse extension that 
transitions to later a later stage of more focused extension, such as occurred 
in West Antarctica, appears to require the presence of a major 
lithosphere-scale boundary and a specific pre-extension thermal state.