MOHO TEMPERATURE AND COMPOSITIONAL CONTROLS ON LITHOSPHERIC BENDING STRENGTH IN THE WESTERN UNITED STATES
Using a range of estimates of crustal heat production values, surface heatflow measurements are extrapolated to depth under the assumption of steady-state conduction, and with the constraint that Pn velocity observations are fit. Preliminary results are very encouraging, and also provide an indication of where Pn velocities are modulated by composition rather than temperature or where the assumption of steady-state heat flow is invalid.
These geotherms are used to predict lithospheric bending strength parameterized as effective elastic thickness, Te, for various assumed rheologies. The model predictions are compared to measurements [Lowry & Pérez-Gussinyé, 2011], to show that a weak, hydrous rheology and/or hydrous partial melt is required to fit observations in the westernmost U.S. The hydrous rheology zone significantly overlaps with the part of North America formed from accreted terranes over the last 300 M.y. To the east of this region, a dryer and stronger rheology is needed to fit the Te observations.