The configuration of mid-ocean ridges subducted below North America prior to Oligocene time is unconstrained by seafloor isochrons and has been primarily inferred from upper-plate geology, including near-trench magmatism. However, many tectonic models are permitted from these constraints. We present a fully kinematic, plate tectonic reconstruction of the NW Cordillera since 60 Ma built by structurally unfolding subducted slabs, imaged by mantle tomography, back to Earth’s surface. We map in three-dimensions the attached Alaska and Cascadia slabs, and a detached slab below western Yukon (Canada) at 400−600 km depth that we call the “Yukon Slab.” Our restoration of these lower plates within a global plate model indicates the Alaska slab accounts for Pacific-Kula subduction since ca. 60 Ma below the Aleutian Islands whereas the Cascadia slab accounts for Farallon subduction since at least ca. 75 Ma below southern California, USA. However, intermediate areas show two reconstruction gaps that persist until 40 Ma. We show that these reconstruction gaps correlate spatiotemporally to published NW Cordillera near-trench magmatism, even considering possible terrane translation. We attribute these gaps to thermal erosion related to ridge subduction and model mid-ocean ridges within these reconstruction gap mid-points. Our reconstructions show two coeval ridge-trench intersections that bound an additional “Resurrection”-like plate along the NW Cordillera prior to 40 Ma. In this model, the Yukon slab represents a thermally eroded remnant of the Resurrection plate. Our reconstructions support a “northern option” Farallon ridge geometry and allow up to ∼1200 km Chugach terrane translation since Paleocene time, providing a new “tomographic piercing point” for the Baja-British Columbia debate.

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Two fully kinematic plate reconstruction files with associated videos, two data tables, and six supporting figures.

<p>One of the greatest challenges of modeling the plate tectonic history of Earth during the Mesozoic and Cenozoic eras lies in reconstructing the Pacific Ocean and its predecessor ocean, Panthalassa.  A major reason for the plate tectonic uncertainty in this region is extensive subduction, which has consumed most (>95%) of the Pacific-Panthalassan ocean lithosphere formed since 150 Ma (Törsvik et al., 2019) and recycled it into the mantle, destroying the information on past plate motions recorded by seafloor magnetic lineations.  Consequently, many circum-Pacific margin plate tectonic models, including the popular GPlates models (e.g. Matthews et al., 2016; Müller et al., 2019), necessarily extrapolate 1000’s of km of subducted seafloor (i.e. synthetic seafloor isochrons).  Given the limited constraints, it is understandable that such models also prefer more straightforward solutions with a smaller number of larger plates, avoiding the complexities of modeling intra-oceanic subduction despite geological evidence from accreted circum-Pacific oceanic terranes.</p><p>Here we build the first topologically-closed, global plate tectonic model of the circum-Pacific using structurally-restored slabs from mantle seismic tomography as our primary constraint.  We use the numerical code TERRA to assimilate three variants of our ‘tomographic’ global plate model into mantle circulation forward models and assimilate the default GPlates model as a reference.  We show our preliminary geodynamic modeling results and test our model predictions against observed mantle structure, Earth’s geoid, and oceanic realm dynamic topography. </p><p>All cases favor plate models that incorporate intra-oceanic subduction within Pacific-Panthalassa, particularly within the northern Pacific.  We find robust support for significant slab lateral advections (i.e. non-vertical slab sinking) under NW Pacific basin.  We discuss similarities and differences between our new ‘tomographic’ plate models and the GPlates model, which has been used for almost all geodynamic studies of the circum-Pacific to date. </p>

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