Some remarks on lithospheric forces and decompression magmatism

Abstract

During lithospheric extension the upwelling mantle melts if it crosses the solidus. To model this process we have used a dynamic model where strain rate varies with time as a function of a constant tensile force. For forces larger than ~ 6–12 TN/m there is after a protracted period with a nearly linear increase in the stretching factor, a short period with rapidly increasing strain rates and adiabatic conditions are effectively realized. The stretching factor at which this is achieved is about 1.1–1.3, increasing with decreasing force. The model could explain the observation of late-stage voluminous magmatism in some rifts and at divergent margins that have evolved for several tens of millions of years.