Toward Reconstructing Mantle Convection Using a Minimum-Continent-Motion Reference Frame

Abstract

Studying geodynamic processes at the plate-mantle interface requires knowledge of how plates move over and subduct into the mantle. The absolute motion of plates relative to the mantle since ∼120 Ma is classically estimated using hotspot tracks. However, for older times only hybrid frames are available that integrate multiple types of constraints, such as trench kinematics, plate velocity, net lithosphere rotation, true polar wander, and eruptions of kimberlites and large igneous provinces. This diminishes the number of independent constraints that we can use to learn about geodynamic processes. Here, we compute absolute plate motions by minimizing absolute continent velocity in a global plate model, in 10 Ma timesteps back to 1 Ga, assuming that continental keels resist relative continent-mantle motion. We estimate uncertainty by adding a ±5 Ma temporal uncertainty to each step and find absolute plate motion is reliable for the last 350 Ma, but not before. The “continent frame” predicts a Cretaceous episode of high net lithosphere rotation due to fast Izanagi plate motion that may signal an anomalously weak NW Pacific upper mantle. Furthermore, the continent frame predicts that Indo-Atlantic hotspots moved parallel to the edges of large low shear velocity provinces and kimberlite eruption sites moved parallel to plate motion. We show that by constructing a global absolute plate motion model based on one assumption, minimal continent motion, allows placing the mantle in a plate tectonic reference frame and unlocks all other constraints of plate-mantle interaction to kinematically reconstruct mantle convection.