A. Rowland et Jh. Davies, Buoyancy rather than rheology controls the thickness of the overriding mechanical lithosphere at subduction zones, GEOPHYS R L, 26(19), 1999, pp. 3037-3040
The thickness of Earth's mechanical lithosphere is poorly defined. To inves
tigate whether rheology controls the thickness of the overriding plate's me
chanical lithosphere in subduction zones, the thermal structure was modelle
d numerically assuming a temperature dependent mantle viscosity. It was fou
nd that the overriding lithosphere was ablated such that very high temperat
ures reached close to the surface near the apex of the wedge corner, leadin
g to unrealistically high heat flow. Since temperature dependent rheology c
learly does not control the thickness of the mechanical lithosphere, we sug
gest that it is instead controlled by buoyancy. The source of buoyancy we a
ssume is compositional, e.g, buoyant crust. Two end-member models with crus
tal thickness of 10 and 70 km respectively were then undertaken, these had
lower heat flow. This work supports the assumption of some earlier workers
(e.g. Plank and Langmuir, 1988) who equated the mechanical lithosphere with
the crust of the overriding plate.