El 27-11-2007, a les 12:00 h., a la Sala de Conferències de l'Institut J. Almera (CSIC), organitzat conjuntament pel CSIC i la UB, El Dr. Vlad Manea, Visiting Associate Seismological Laboratory CalTech, Pasadena, dels EEUU d'Amèrica, impartirà la conferència Role of low viscosity wedges and channels in the evolution of subducting systems

Comentaris: Dehydration of subducting lithosphere likely transports fluid into the mantle wedge where the viscosity is decreased. Such a decrease in viscosity could form a low viscosity wedge (LVW) or a low viscosity channel (LVC) on top of the subducting slab. Using numerical models, we investigate the influence of low viscosity wedges and channels on subduction zone structure. Slab dip changes substantially with the viscosity reduction within the LVWs and LVCs. For models with or without trench rollback, overthickening of slabs is greatly reduced by LVWs or LVCs. Two divergent evolutionary pathways have been found depending on the maximum depth extent of the LVW and wedge viscosity. Assuming a viscosity contrast of 0.1 with background asthenosphere, models with a LVW that extends down to 400 km depth show a steeply dipping slab, while models with an LVW that extends to much shallower depth, such as 200 km, can produce slabs that are flat lying beneath the over-riding plate.
There is a narrow range of mantle viscosities that produces flat slabs (5 to10 x1019 Pa s) and the slab flattening process is enhanced by trench rollback. Slab can be decoupled from the overriding plate with a LVC if the thickness is at least a few 10s of km, the viscosity reduction is at least a factor of two and the depth extent of the LVC is several hundred km. These models have important implications for the geochemical and spatial evolution of volcanic arcs and the state of stress within the over-riding plate. The models explain the poor correlation between traditional geodynamic controls, subducting plate age and convergence rates, on slab dip. We predict that when volcanic arcs change their distance from the trench, they could be preceded by changes in arc chemistry. We predict that there could be a larger volatile input into the wedge when arcs migrate toward the trench and visa-versa. The transition of a subduction zone into the flat lying regime could be preceded by change.