Marton, F. C., C. R. Bina, S. Stein, and D. C. Rubie, Are all Phi created equal?, Eos, Transactions of the American Geophysical Union, 78, Fall Supplement, F662, 1997.
A classic parameterization of subduction zone thermal structure is that for simple thermal models the depth to which isotherms penetrate should vary with the thermal parameter Phi: the product of age of the subducting lithosphere at the trench, convergence rate, and dip angle. Observations of subduction zones show that although the depth of the deepest seismicity increases with Phi, it is not a continuous function of Phi. The deepest earthquakes jump from about 300 km to >600 km at Phi ~ 5000 km. In general terms, modeling of subducting slabs suggests that metastable wedges of olivine, which may provide conditions necessary for deep seismicity, should grow increasingly larger and deeper as a function of Phi. Given the observed complex variation of seismicity with depth, it is natural to explore further how the thermal and mineralogical structures of slabs vary with changes in the constituents of Phi rather than simply with Phi itself.
We examine the temperature fields of a set of model subducting slabs of constant Phi and age, but we vary the convergence rate and dip of the slab, both with and without the latent heat of transformation of alpha (olivine) to beta (wadsleyite) or gamma (ringwoodite), to analyze the roles of these variables. These models are then compared to the distribution of seismicity for subduction zones with comparable thermal parameters. We also examine the shape and size of the predicted metastable wedge as a function not only of the components of Phi but also of the uncertainties in both the temperature models and the kinetic rate laws that govern the olivine transformations.Copyright © 1997 American Geophysical Union