Reconstructing plate motions of subducted oceanic plates using paleomagnetic data from subduction complexes – with examples from Japan, New Zealand, Mexico and Costa Rica

Dr. Lydian Boschman, Postdoc
ETH Zurich – Department of Environmental Systems Sciences

Wednesday, April 14th, 2021
watch Dr. Boschman’s talk

Compared to continental lithosphere, oceanic lithosphere has a limited lifespan at the Earth’s surface. With the continuous generation of new oceanic lithosphere at mid-ocean ridges, balanced by the consumption of older oceanic lithosphere in subduction zones, oceanic lithosphere at the surface is renewed every ~200 Myr. This implies that the lithosphere that was underlying ancestral oceans has largely been lost to subduction. As a result, deep-time plate tectonic reconstructions rely primarily on geological, paleontological and paleomagnetic data from the continents. Such reconstructions portray the distribution of continents through geological time, but lack information on plate motions and plate geometry in the oceanic domains. The key to improve such deep-time plate kinematic reconstructions, which are crucial in understanding for example whole-Earth mantle convection or true polar wander, is restoration of lost oceanic plates, albeit highly challenging.
In this presentation, I will focus on the plate kinematic history of the Mesozoic Panthalassa Ocean, the predecessor of the modern Pacific Ocean, which surrounded the supercontinent Pangea. Even though the former Panthalassa plates are no longer at the surface, their formation and demise has left an imprint upon the Earth and their plate motions can be reconstructed from indirect sources of data. First, marine magnetic anomalies and fracture zones preserved on the Pacific Plate provide constraints on the past motions of plates conjugate to the Pacific Plate (the conceptual Izanagi, Farallon and Phoenix plates) back to ~190 Ma. Second, remnants of oceanic ridges, rises, seamounts, and intra-oceanic arcs, scraped off the downgoing plates during subduction and presently exposed in circum-Pacific accretionary complexes, enables the acquisition of geological and paleomagnetic data from the rock record representative of the former Panthalassa plates. Such accreted materials range from fragments to entire sequences of ‘Ocean Plate Stratigraphy’ (OPS), which provide valuable geological information on the age and nature of lost oceanic plates. Moreover, paleomagnetic data from OPS rocks may provide paleolatitudes of the subducted oceanic plate, thereby constraining latitudinal plate motion.
Here, we present a plate kinematic reconstruction of the Panthalassa Ocean using new paleomagnetic data from accreted Permian to Cretaceous OPS rocks exposed in the accretionary complexes and subduction mélanges of Cedros Island (Baja California, Mexico), the Santa Elena Peninsula (Costa Rica), the North Island of New Zealand, and Japan, yielding plate motions of the Farallon, Phoenix and Izanagi plates, respectively. We develop a plate reconstruction since 260 Ma that satisfies the available paleomagnetic data and is consistent with constraints from upper plate deformation and accretion in the circum-Pacific continental margins. This work explores the possibility of developing reconstructions of subducted oceanic plates using paleomagnetic data, and develops a method that may be applied to any other ancient lost ocean, as long as associated accretionary complexes are identified exposing off-scraped remnants of the former oceanic plates.