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The amalgamation of Laurentia’s Archean provinces ca. 1830 Ma was followed by ~700 m.y. of accretionary orogenesis along its active southeastern margin, marked by subduction of oceanic lithosphere, formation of arcs and back-arcs, and episodic accretion. This prolonged period of active-margin tectonic processes, spanning the late Paleoproterozoic and Mesoproterozoic eras, resulted in major accretionary crustal growth and was terminated by closure of the Unimos Ocean (new name). Ocean closure was associated with rapid motion of Laurentia toward the equator and resulted in continental collision that led to profound reworking of much of the accreted Proterozoic crust during the ca. 1090–980 Ma Grenvillian orogeny. The Grenvillian orogeny resulted in formation of a large, hot, long-duration orogen with a substantial orogenic plateau that underwent extensional orogenic collapse before rejuvenation and formation of the Grenville Front tectonic zone. The Grenvillian orogeny also caused the termination and inversion of the Midcontinent Rift, which, had it continued, would likely have split Laurentia into distinct continental blocks. Voluminous mafic magmatic activity in the Midcontinent Rift ca. 1108–1090 Ma was contemporaneous with magmatism in the Southwestern Laurentia large igneous province. We discuss a potential link between prolonged subduction of oceanic lithosphere beneath southeast Laurentia in the Mesoproterozoic and the initiation of this voluminous mafic magmatism. In this hypothesis, subducted water in dense, hydrous Mg-silicates transported to the bottom of the upper mantle led to hydration and increased buoyancy, resulting in upwelling, decompression melting, and intraplate magmatism. Coeval collisional orogenesis in several continents, including Amazonia and Kalahari, ties the Grenvillian orogeny to the amalgamation of multiple Proterozoic continents in the supercontinent Rodinia. These orogenic events collectively constituted a major turning point in both Laurentian and global tectonics. The ensuing paleogeographic configuration, and that which followed during Rodinia’s extended breakup, set the stage for Earth system evolution through the Neoproterozoic Era.

A new regional S‐velocity study resolving the Eurasia-Africa plate boundary region from the Azores to the eastern Mediterranean Sea is presented. The resolution of existing velocity models has been complemented by using new seismic broad‐band data recorded by the temporary MIDSEA network and at permanent European seismic stations. Following the partitioned waveform inversion method, we interactively fitted the waveforms of S and Rayleigh wave trains of more than 1100 seismograms. The linear constraints on upper‐mantle S velocity provided by the waveform fits have been combined with independent estimates of Moho depth in a linear damped least‐squares inversion for S velocity and crustal thickness. The resulting S‐velocity structure for the Mediterranean Sea shows strong lateral variations, confirming the complex evolution of this plate boundary region. The upper mantle along the Eurasia-Africa suture zone is characterized by high‐velocity material representing subducted oceanic lithosphere. This signature can be followed to depths of 300-500 km, depending on the region and resolution. A high‐velocity body, possibly representing a fragment of subducted lithosphere, has been imaged beneath eastern Spain at a depth between 250 and 500 km. Not only convergence has been recorded in the upper mantle, but extension also has its own signature beneath the Mediterranean region. This is particularly clear for the Algero‐Provençal and Tyrrhenian basins, where a shallow asthenospheric layer is observed. The lithosphere-asthenosphere system of the western Mediterranean clearly differentiates itself from the structure of the older eastern Atlantic Ocean. Differences in comparison to the structure of a 4 to 20 Ma ocean are also present. These observations support the idea that, rather than a young ocean, the western Mediterranean could be a strongly stretched continent, partly affected by spreading, formed at the back of a slab. The structure characterizing the eastern Mediterranean points to a continuation of the northern African continental lithosphere beneath the sea. Major structural differences in the eastern Atlantic Ocean are imaged between the mid‐Atlantic ridge and the older oceanic basins: the north Atlantic lithosphere is characterized by lower velocities beneath the spreading ridge than under the old ocean basins. Despite the strong differences observed in the crustal structure between the mid‐Atlantic ridge and the Azores, no significant differences are observed in the S‐velocity structure of the upper mantle