A MECHANISM FOR CRUSTAL RECYCLING ON VENUS

Entrainment of lower crust by convective mantle downflows is proposed as a crustal recycling mechanism on Venus. The mechanism is characteri zed by thin sheets of crust being pulled into the mantle by viscous fl ow stresses. Finite element models of crust/mantle interaction are use d to explore tectonic conditions under which crustal entrainment may o ccur. The recycling scenarios suggested by the numerical models are an alogous to previously studied problems for which analytic and experime ntal relationships assessing entrainment rates have been derived. We u se these relationships to estimate crustal recycling rates on Venus. E stimated rates are largely determined by (1) strain rate at the crust/ mantle interface (higher strain rate leads to greater entrainment); an d (2) effective viscosity of the lower crust (viscosity closer to that of mantle lithosphere leads to greater entrainment). Reasonable geolo gic strain rates and available crustal flow laws suggest entrainment c an recycle almost-equal-to 1 km3 of crust per year under favorable con ditions.