Thermal structure due to solid-state flow in the mantle wedge beneath arcs

Abstract

We summarize petrological and seismic constraints on the temperature of arc lower crust and shallow mantle, and show that published thermal models are inconsistent with these constraints. We then present thermal models incorporating temperature-dependent viscosity, using widely accepted values for activation energy and asthenospheric viscosity. These produce thin thermal boundary layers in the wedge corner, and an overall thermal structure that is consistent with other temperature constraints. Some of these models predict partial melting of subducted sediment and/or basalt, even though we did not incorporate the effect of shear heating We obtain these results for subduction of 50 Myr old oceanic crust at 60 km/Myr, and even for subduction of 80 Myr old crust at 80 km/Myr, suggesting that melting of subducted crust may not be not restricted to slow subduction of young oceanic crust.

Late Triassic high-Mg andesite/dacite suites from northern Hohxil, North Tibet: Geochronology, geochemical characteristics, petrogenetic processes and tectonic implications

“…The compositional disequilibrium characteristics of the augites suggest that the Hohxil high-Mg andesites were likely derived by interaction between melts and mantle (e.g., Rapp et al, 1999;Yogodzinski and Kelemen, 1998). However, the origin of the melts requires further clarification, given that similar melts have been attributed to partial melting of delaminated or subducted continental crust (e.g., Gao et al, 2004;Wang et al, 2006bWang et al, , 2008cXu et al, 2008), subducted basaltic oceanic crust, or sediments (e.g., Kay et al, 1993;Kelemen et al, 2003;Shimoda et al, 1998;Tatsumi, 2001;Tatsumi and Hanyu, 2003;Yogodzinski and Kelemen, 1998;Yogodzinski et al, 1994Yogodzinski et al, , 1995.…”

Rheologic controls on slab dynamics

“…Localized regions of low viscosity caused by high water or melt content in the mantle wedge could allow the hot mantle to advect to shallower depths and thereby decrease the length of the coupled plate boundary [Kelemen et al, 2003], or could decrease the magnitude of the dynamic pressure in the wedge corner [Billen et al, 2003]. Both effects would lead to steeper slab dips.…”

“…The thermal structure of the plate directly above the slab is most important for the slab evolution. While the age of overriding plates varies significantly, the island arc region is thought to have temperatures of 1200-1400°C at depths of 50 km due in part to convective erosion from melt and volatile weakening of the overriding lithosphere [Kelemen et al, 2003;Arcay et al, 2007; A.-M. Cagnioncle et al, The effect of solid flow above a subducting slab on water distribution and melting at convergent plate boundaries, submitted to Journal of Geophysical Research, 2007]. Therefore a warm and thin overriding plate is appropriate and it is assigned an initial thermal structure determined by a half-space cooling model for a 40 my old plate.…”

Intermediate to felsic middle crust in the accreted Talkeetna arc, the Alaska Peninsula and Kodiak Island, Alaska: An analogue for low‐velocity middle crust in modern arcs

“…The Triassic to Jurassic arc is exposed in four volcanic and plutonic sections in the Chugach Mountains, the Talkeetna Mountains, the Kodiak archipelago and the Alaska Peninsula (Figure 1). Previous research has principally focused on the Chugach Mountains, which preserve a faulted crustal section from residual subarc mantle to subaerial volcanic rocks [DeBari and Coleman, 1989;Kelemen et al, 2003aKelemen et al, , 2003bMehl et al, 2003;Behn and Kelemen, 2006;Greene et al, 2006;Hacker et al, 2008]. The Jurassic batholith on the Alaska Peninsula is distinctly more felsic than the crustal section in the Chugach Mountains and has the potential to provide new insight into the role of silicic magmas in intraoceanic settings.…”