Van Ark, E. M., F. C. Marton, C. R. Bina, S. A. Stein, and D. Rubie, Survival of metastable olivine in detached slabs: Difficult but not impossible, Eos, Transactions of the American Geophysical Union, 79, Spring Supplement, S164, 1998.
Some deep earthquakes occur in slabs which appear detached from near-surface manifestations of subduction. One example is the deep seismicity beneath the North Fiji Basin, thought to occur in a slab of former Pacific plate subducted at the Vitiaz trench which later detached during a late Miocene arc reversal. An analogous situation is suggested by the third-largest deep earthquake in the instrumental record, which occurred beneath Southern Spain in 1954, presumably in a slab detached after an earlier regime of subduction in the complex boundary between the Africa and Eurasia plates. It has been suggested that such earthquakes result from transformational faulting in metastable olivine regions which persist for some time after slab detachment occurred. We examine this possibility using thermo-kinetic modeling to explore how long regions of metastable olivine should persist for plausible combinations of the time since ceassation of subduction, age of the subducted lithosphere, subduction rate, and hence thermal structure of the slab at detachment. The survival of a significant metastable region for times on the order of 10 Myr appears to depend crucially on the thermal structure, implying that (as observed) such seismicity may be a relatively rare phenomenon.Copyright © 1998 American Geophysical Union