NW Pacific‐Panthalassa Intra‐Oceanic Subduction During Mesozoic Times From Mantle Convection and Geoid Models.

Pacific‐Panthalassa plate tectonics are the most challenging on Earth to reconstruct during the Mesozoic and Cenozoic eras due to extensive subduction, which has resulted in large (>9,000 km length) unconstrained gaps between the Pacific and Laurasia (now NE Asia) back to the Early Jurassic. We build four contrasted NW Pacific‐Panthalassa global plate reconstructions and assimilate their velocity fields into global geodynamic models. We compare our predicted present mantle structure, synthetic geoid and dynamic topography to Earth observations. P‐wave tomographic filtering of predicted mantle structures allows for more explicit comparisons to global tomography. Plate reconstructions that include intra‐oceanic subduction in NW Pacific‐Panthalassa fit better to the observed geoid and residual topography, challenging popular models of Andean‐style subduction along East Asia. Our geodynamic models predict significant SE‐ward lateral slab advections within the NW Pacific basin lower mantle (∼2,500 km from Mesozoic times to present) that would confound "vertical slab sinking"‐style restorations of imaged slabs and past subduction zone locations. Plain Language Summary: Our knowledge of Earth's past tectonic plate configurations becomes increasingly uncertain going back into geologic time. Northwest Pacific‐Panthalassa plate tectonics along East Asia and the northern Pacific margin are among the most uncertain place on Earth to reconstruct during the Mesozoic‐Cenozoic eras. Numerous hypotheses have been proposed: one popular hypothesis suggests a large oceanic plate subducted continuously and exclusively under the eastern margin of Asia throughout Jurassic and Cretaceous times (i.e., Andean‐type subduction); a second hypothesis assumes that a number of smaller plates existed within the Northwestern Pacific that subducted both under the Asian margin and at offshore subduction zones (i.e., intra‐oceanic subduction). Using numerical models of mantle convection, we computed where each hypothesis predicts the subducted lithospheric plates to be at present in the Earth's interior. We compared these predictions against tomographic images of the Earth's mantle. We also calculated the gravitational attraction caused by the predicted mass distributions and compared them against the observed geoid. The warping of the Earth's surface caused by mantle flow was also computed and compared against non‐hydrostatic topography measurements. Our results favor plate reconstructions featuring intra‐oceanic subduction within Northwestern Pacific‐Panthalassa, with implications for past global CO2 and reconstructing disappeared ocean basins. Key Points: Six fully kinematic, end‐member western Pacific plate tectonic reconstructions were assimilated into global geodynamic modelsIntra‐oceanic subduction in western Pacific produces synthetic geoid and dynamic topography best fit observed geoid and residual topographyGeodynamic models predict significant SE‐ward lateral slab advections within NW Pacific lower mantle (∼2,500 km from Jurassic to present) [ABSTRACT FROM AUTHOR]