The Dynamic History of 220Million Years of Subduction Below Mexico: A Correlation Between Slab Geometry and Overriding Plate Deformation Based on Geology, Paleomagnetism, and Seismic Tomography

Global tectonic reconstructions of pre-Cenozoic plate motions rely primarily on paleomagnetic and geological data from the continents, and uncertainties increase significantly with deepening geological time. In attempting to improve such deep-time plate kinematic reconstructions, restoring lost oceanic plates through the use of geological and seismic tomographical evidence for past subduction is key. The North American Cordillera holds a record of subduction of oceanic plates that composed the northeastern Panthalassa Ocean, the large oceanic realm surrounding Pangea in Mesozoic times. Here we present new paleomagnetic data from subduction-related rock assemblages of the Vizcaino Peninsula of Baja California, Mexico, which yield a paleolatitudinal plate motion history equal to that of the North American continent since Late Triassic time. This indicates that the basement rocks of the Vizcaino Peninsula formed in the forearc of the North American Plate, adjacent to long-lived eastward dipping subduction at the southern part of the western North American continental margin. Tomographic images confirm long-lived, uninterrupted eastward subduction. We correlate episodes of overriding plate shortening and extension to flat and steep segments of the imaged slab. By integrating paleomagnetic, geological, and tomographic evidence, we provide a first-order model that reconciles absolute North American plate motion and the deformation history of Mexico since Late Triassic time with modern slab structure. Plain Language Summary Reconstruction of deep-time global tectonic plate motions relies primarily on data derived from the rock record of the continents, as the vast majority of pre-Cenozoic oceanic crust has been recycled into the Earth's mantle in subduction zones. To improve deep-time plate tectonic reconstructions, adding information on the plate motions and the geometry of lost oceanic plates is therefore key. In this study, we attempt at reconstructing the subduction of oceanic plates of the eastern Panthalassa Ocean, which surrounded the supercontinent Pangea. We present new paleomagnetic data from the geological record of the Vizcaino Peninsula of central Baja California and conclude that the Vizcaino peninsula has since 220Ma been part of the North American Plate below which the Panthalassa plates subducted. Furthermore, we analyze mantle tomographic images, illustrating the presence of an extraordinary long anomaly interpreted as subducted lithosphere. By integrating geological, paleomagnetic, and seismic tomographic data, we present a model that reconciles absolute North American plate motion and the deformation history of Mexico since the Triassic with modern slab structure.