Intra-Plate Deformation of the Pacific: Evidence from Oceanic Plateaux and Geodynamic Models

The theory of plate tectonics acknowledges that drifting lithospheric plates are rigid and do not undergo substantial deformation except near or at plate boundaries. However, studies have shown that intra-plate deformation is a feature for continental lithosphere and can originate from different mechanisms such as lithospheric drips, delamination, and in-plane stresses. On the other hand, there is not well-known understanding of tectonic deformation within the interior of ocean plates. We compile data to show there is geological and geophysical evidence documenting that the drifting Pacific plate has been undergoing appreciable extensional deformation at the locations of its oceanic plateaux. Namely, the Ontong Java, Shatsky Rise, Hess Rise, and Manihiki plateaux show extensive evidence for normal faults, horst-graben structures, and extension related magmatic activity at a significant distance from plate boundaries. Furthermore, this deformation occurred after the initial emplacement of their associated large igneous provinces (LIPs) and before their arrival to subduction zones.

We present numerical geodynamic experiment results demonstrating that terranes embedded in ocean plates can undergo extensional deformation prior their accretion to the overriding plate due to slab-pull (e.g., a “subduction pulley”).  Our numerical models show that the subduction pulley is also a valid mechanism for the extensional deformation of the Pacific oceanic plateaux even at remote locations from the plate boundaries. For instance, tensional stress originated from down-going slabs can be transmitted through strong oceanic lithosphere over long distances (>1000 km) and deform the plate at its weak oceanic plateaux regions. The numerical experiments further demonstrate that high crustal thickness reduces the bulk strength of ocean lithosphere at the location of oceanic plateaux and makes them susceptible to slab-pull related extension—manifesting on the surface as intra-ocean plate deformation.