Do continental lithospheric discontinuities exert control on tectonic plate motion directions?

Abstract

Plate motion directions, and the orientations of rift zones and oceanic spreading ridges, and of transform faults and fracture zones that are perpendicular to these ridges, are generally controlled by tectonic forces such as slab pull, mantle convection, and mantle plumes. Here, it is hypothesized that within the confines of these general orientations, the exact orientations of these structures, and therefore plate motion directions, are partially controlled by suitably oriented sets of steep continental lithospheric discontinuities (CLDs), which work in concert with these larger tectonic forces.

Previously, the observation has been made that oceanic fracture zones are contiguous with CLDs, such as suture zones and other lithospheric fault zones. Based on high-resolution bathymetry, geological and geophysical data, it is demonstrated here that continents have multiple sets of lineaments parallel to such CLDs, or contiguous with CLDs where they occur farther inland and do not reach the ocean. Published analog experiments suggest that the orientations of transform faults and fracture zones are controlled by these CLDs if the angle between the spreading direction and the CLDs is no more than ∼45°. Spreading ridge segments evolve in an orientation perpendicular to these transform faults and fracture zones, so that the spreading direction becomes parallel to the transform faults and fracture zones. The implication is that the exact plate motion directions are controlled by CLDs, if a set of CLDs is orientated at low angle with the spreading direction. When plate motion directions need to change due to tectonic forces, the new hypothesis predicts that the exact directions may be controlled by a different set of suitably orientated CLDs. During later stages of oceanic spreading, the larger tectonic forces such as slab pull, mantle convection, and mantle plumes become increasingly dominant and plate motion directions may no longer be controlled by the CLDs.

While the hypothesis needs further testing, it has potentially far-reaching implications. For example, Euler pole reconstructions are commonly based on small circle patterns formed by fracture zones and transform faults in the oceanic lithosphere. Oceanic crust older than ∼200 Ma is typically destroyed by subduction, and pre-Mesozoic Euler poles can therefore not be reconstructed based on that method. If the hypothesis presented above is correct, the orientations of CLDs and associated lineament sets may be used as proxies for orientations of past transform faults and fracture zones, at least during early oceanic spreading. The locations of past Euler poles may thus be better estimated based on these CLDs and lineaments, and pre-Mesozoic plate tectonic reconstructions may be much improved in deep geologic time.