Thermal state of earth's mantle during accretion
Abstract
We investigate the thermal evolution of the Earth's mantle during accretion, assuming that the initial proto-Earth grows by accreting 25 Moon to Mars-sized planetary embryos in 100 Myr. The initial proto-Earth is a differentiated planetary embryo with a liquid iron core of 1670 km radius overlain by a silicate mantle of 3430 km radius. Each embryo is assumed to impact vertically with a modified escape velocity and completely merges to the proto-Earth. The impact heating creates a large partially molten magma pond in the mantle beneath the impact site that directly interacts with the core. The iron content of the embryo sinks through the pond and merges to the core, while the partially molten buoyant silicate with temperatures higher than the stiff magma temperature pours out and spreads on the proto-Earth, forming a superheated global magma ocean. The ocean cools to the atmosphere by convection until it behaves like solid, and then cools by thermal conduction. The successive embryo impacts result in overlapping high temperature solidified magma oceans with thicknesses of 70-135 km, which hamper the creation of global mantle convection. We examine the effects of a few key physical parameters; the kinetic viscosity of the magma ocean, the total accretion time, the impact velocities of the embryos, the atmospheric temperature, and the impact time intervals using 12 thermal evolution models. The high temperature solid surface layers are the main characteristics of all of the models. It takes about 150 Myr after the accretion for the mantle to create a global convection.
- Publication:
-
Physics of the Earth and Planetary Interiors
- Pub Date:
- October 2022
- DOI:
- 10.1016/j.pepi.2022.106925
- Bibcode:
- 2022PEPI..33106925A
- Keywords:
-
- Impact;
- Accretion;
- Magma ocean;
- Convection;
- Mantle