Reconstructing lost plates of the Panthalassa Ocean

Abstract

Compared to continental lithosphere, oceanic lithosphere has a limited lifespan at the Earth’s surface. As a result of its continuous subduction and formation at mid-ocean ridges, modern oceanic crust is almost nowhere older than ~200 Ma. This implies that the lithosphere that was underlying ancestral oceans, such as the Panthalassa Ocean surrounding Pangea during its culmination in late Paleozoic – early Mesozoic times, has (almost) all 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 plates that host continents through geological time, but generally lack (or include only conceptual) plate motions and -geometry in the oceanic domains. In this thesis, approaches are developed and data is collected that improve deep-time global plate kinematic reconstructions of the Panthalassa Ocean through quantitative restoration of lost oceanic plates. First, all available data from oceanic lithosphere of the present-day descendant of the Panthalassa, the Pacific Ocean, that did not (yet) subduct is used. The oldest part of the Pacific Plate, which originated in Jurassic time, contains magnetic lineations in three orientations that constrain relative plate motions of three conceptual plates conjugate to the Pacific (Izanagi in the northeast, Farallon in the northeast and Phoenix in the south) back to ~190 Ma. In chapter 1, the plate tectonic configuration that led to the birth of the Pacific Plate is reconstructed. Second, the location and tectonic nature of the boundaries of the Panthalassa Ocean through time are defined, which relies on reconstruction of Pangea’s (and post-Pangea’s) external trenches relative to the surrounding continents, and involves the restoration of complex crustal deformation at subduction plate boundary zones. In chapters 2-5 regional reconstructions are presented of the Pacific margin of Mexico and Caribbean region. The third step involves the use of data from fully subducted lithosphere. This includes paleomagnetic and stratigraphic data from ‘Ocean Plate Stratigraphy’ materials that were scraped off during subduction and are now exposed in the circum-Panthalassa accretionary complexes. Furthermore, seismic tomographic images reveal the locations of subducted material in the mantle that are correlated to reconstructed intra-oceanic or continental margin subduction zones, thereby constraining the position of these subduction zones relative to the mantle. Chapters 6 and 7 present reconstructed Permian-Cretaceous plate motions of the Farallon, Izanagi and Phoenix plates based on paleomagnetic data from OPS remnants exposed in the accretionary prisms of Mexico, Costa Rica, Japan and New Zealand, as well as of an intra-oceanic subduction zone of which the remnant arc is exposed in Japan.