Relationship between Subduction Regime and Back Arc Dynamics

Abstract

In all experiments presented in the previous chapter densities of the lithosphereρland the asthenosphere ρ_aare equal. Such a condition corresponds to reality only to a first approximation. In fact, ρ_l may be either less than or greater than ρ_a. The lithospheric density depends on many factors, the “thermal” age being the most important one[Oxburgh and Parmentier, 1977;Oxburgh and Turcotte, 1976;England and Wortel, 1980]. The greater the age of lithosphere (i.e., the colder and thicker it is), the higher its average density p _l. Estimates for $\Delta \rho (\Delta \rho = {\rho _l} - {\rho _a})$ vary from very small values to those in excess of 0.1 x 10³kg/m³[Yoshii, 1973;Toksoz et al., 1973;Grow, 1973;Watts and Talwani, 1975]. The average lithospheric and asthenospheric densities become equal when the age of the oceanic lithosphere reaches about 50 Ma[Oxburgh and Parmentier, 1977;Molnar and Atwater, 1978;England and Wortel, 1980;Sacks, 1983].