Subduction zone rheology

Rheological flow laws can be obtained from studies using multi-anvil high-p ressure systems with synchrotron-based piezometers and strain metrics. The high flux X-ray source provides minute-scale time resolution with accurate measurement of diffraction patterns and direct sample images. Measurements of length changes with an accuracy of one part in 10(4) are being developed and will provide a new generation of theological tools. Flow laws derived from peak broadening agree well with literature data for corundum, spinel, and olivine. Properties of several mantle phases are compared for the temperature and pr essure regime appropriate to a subducting slab. Temperature dependence of t hese properties exhibits a strong, temperature insensitive low temperature region, a thermally softened region and a weak high temperature region. The middle of these could be related to the seismogenic zone of a subduction z one. The progression of the temperature for softening with mineral phase su ggests that earthquakes deeper than 400 km correspond to higher temperature s than for olivine in the upper 400 km. Plastic instabilities are suggested by these data as the origin of deep earthquakes. (C) 2001 Elsevier Science B.V. All rights reserved.