Stability and growth of continental shields in mantle convection models including recurrent melt production

Abstract

The long-term growth and stability of compositionally layered continental upper mantle has been investigated by numerical modelling. We present the first numerical model of a convecting mantle including differentiation through partial melting resulting in a stable compositionally layered continental upper mantle structure. This structure includes a continental root extending to a depth of about 200 km. The model covers the upper mantle including the crust and incorporates physical features important for the study of the continental upper mantle during secular cooling of the Earth since the Archaean. Among these features are: a partial melt generation mechanism allowing consistent recurrent melting, time-dependent non-uniform radiogenic heat production, and a temperature-and pressure-dependent rheology. The numerical results reveal a long-term growth mechanism of the continental compositional root. This mechanism operates through episodical injection of small diapiric upwellings from the deep layer of undepleted mantle into the continental root which consists of compositionally distinct depleted mantle material. Our modelling results show the layered continental structure to remain stable during at least 1.5 Ga. After this period mantle differentiation through partial melting ceases due to the prolonged secular cooling and small-scale instabilities set in through continental delamination. This stable period of 1.5 Ga is related to a number of limitations in our model. By improving on these limitations in the future this stable period will be extended to more realistic values.

The Role of History-Dependent Rheology in Plate Boundary Lubrication for Generating One-Sided Subduction

“…To check the effect of the maximum viscosity truncation on the solutions, we performed calculations with varying value of the truncation viscosity g 0 (10 24 PaÁs, 3 Â 10 24 PaÁs, and 10 26 PaÁs) under the same condition in the other parameters as that of Case ST1 (g 0 ¼ 10 25 PaÁs) although this maximum viscosity truncation is commonly used in the previous studies (e.g., DE SMET et al, 1998;TETZLAFF and SCHMELING, 2000). The features obtained for the subduction structure and the evolution history were very similar to each other.…”

Dynamic recrystallization and strain softening of olivine aggregates in the laboratory and the lithosphere

“…The water content of continental lithosphere is expected to be more variable. Continental cratonic lithosphere formed by accretion of asthenosphere diapirs (de Smet et al 1998) should be dry owing to extensive melting (Karato 2003), but as continental lithosphere ages it can become progressively hydrated by infiltrating fluids. It is likely that hydrous regions such as the mantle wedge above subduction zones and hydrated lithospheric shear zones are strongly water weakened (Karato & Wu 1993;Kohlstedt et al 1995;Hirth & Kohlstedt 2003).…”

Global-scale modelling of melting and isotopic evolution of Earth's mantle: melting modules for TERRA

“…After that study was published, many followed a similar approach, either tracking preset heterogeneities (e.g. Davies, 2002;Zhong and Hager, 2003;Nakagawa and Tackley, 2004), or having the chemical heterogeneities emerge via melting during the calculation at fixed melting zones (Walzer and Hendel, 1999;Davies, 2002;Huang and Davies, 2007a, b, c), moving melting zones that follow force-balanced plates or imposed plate motions (Brandenburg and van Keken, 2007a, b;Brandenburg et al, 2008), or freely moving melting location via a melting phase diagram (De Smet et al, 1998;Van Thienen et al, 2004;Xie and Tackley, 2004a, b;Nakagawa et al, 2009Nakagawa et al, , 2010.…”