Simulation of the metamorphic and deformational history of the metamorphic sole of the Oman Ophiolite

Abstract

Emplacement of ophiolites onto less dense continental crust is an enigma. The rates of emplacement, the mechanisms of emplacement, and the stress and temperature histories of the rocks are all incompletely understood. The Oman ophiolite is well exposed and has been studied extensively by field geologists. An integrated thermal and kinematic model of the temperature, stress, rock type, and displacement fields during the early stages of the emplacement of the Oman ophiolite is developed here to explain field relations and provide insight into the development of the metamorphic rocks at the base of the ophiolite. The thermal evolution was calculated by a finite difference algorithm for heat conduction, considering heats of metamorphic reactions, deformational heating, and heat advection by rock. The stress and displacement fields were calculated by an analytical model using a velocity boundary condition, power law constitutive relations, and a brittle frictional sliding relationship. In simulations involving young, hot subducted lithosphere, a wider portion of the subduction zone deforms by power law creep, and deformation occurs at lower stresses and slower strain rates, minimizing the deformational heating compared to colder, older subducted lithosphere. Dehydration occurs at an accelerated rate in younger, hotter lithosphere, removing heat from the subducted plate at an earlier stage and causing the zone of brittle deformation to propagate downward more rapidly. Power law creep of subducted basaltic rocks is limited to temperatures greater than 500°C and occurs at differential stresses of the order of 100 MPa. The simulations predict that metamorphic field gradients and the spatial distribution of rock types in the metamorphic sole of Tethyan ophiolites might be used to infer the emplacement direction of the ophiolite.