Rheology of the plate interface — Dissolution precipitation creep in high pressure metamorphic rocks

Abstract

Subduction zone models invoke deformation to be concentrated along the plate interface, in a region of particularly low temperature. Geophysical observations do not provide constraints on temperature, stress and deformation patterns with desired resolution. In contrast, the record of high pressure metamorphic rocks exhumed from subduction zones provides details on P–T-history, deformation mechanisms, and stress state, albeit not readily correlated with the former dynamic situation on larger scale. Here we review available information on dissolution precipitation creep (DPC) in high pressure metamorphic rocks, which – if representative for subduction zones in general – can pose constraints on conditions, rheology, and flow patterns along the plate interface. The key observations and conclusions are that: (1) Deformation is typically highly inhomogeneous and localized into shear zones; (2) stresses are generally too low to drive crystal plastic deformation; (3) microfabrics suggest dissolution precipitation creep to be the predominant deformation mechanism; (4) an aqueous fluid at quasi-lithostatic pressure is available throughout, allowing for tensile fracturing and crack healing or sealing; (5) low stress combined with high strain rates required for localized deformation at typical subduction rates implies low viscosity; and (6) contribution of shear heating to the thermal budget of subduction zones should be moderate. The dominant deformation mechanism DPC is reviewed in some detail, including experimental and theoretical approaches. Various examples of DPC in high pressure metamorphic rocks are illustrated, emphasizing the role of interphase boundaries as sites of dissolution. Rheology governed by DPC is proposed to control interplate coupling and development of a subduction channel with return flow, being a likely candidate for rapid exhumation of high pressure metamorphic rocks.