Intraoceanic subduction drove both the Pacific plate’s ~80- to 47-Ma northward motion and its redirection at ~47 Ma.

The vestiges of the pre-Caledonian magma-poor hyperextended margin of Baltica are preserved in a mélange zone in southern Norway. The rock assemblage in the distal domains of magma-poor hyperextended margins includes extensional allochthons and basement slivers, which share a pre-rift tectonometamorphic history with the non-rifted basement. After incorporation into an orogenic belt, these distinct fingerprints may be used to test whether such heterogeneous mélange units were derived from the basement units below or have been transported to the orogen from elsewhere. Later magmatic additions and tectonometamorphic events may provide additional information on the geological evolution of the margin. We present U–Pb results from 12 gneisses and meta-igneous rocks from the mélange zone. We find Proterozoic gneisses of Telemarkian affinity over the length of the mélange zone that support the formation of the mélange along the ancient Baltican margin. We also find latest Cambrian–early Ordovician meta-igneous rocks that may be linked either to shortening of transitional crust formed in the Ediacaran or, alternatively, to an episode of extension in the Ordovician. Scandian thrusting initiated between 438 and 427 Ma and was followed by the emplacement of syntectonic ‘Scandian’ granitoids at 421 Ma; that emplacement coincides with peak metamorphism. Supplementary material: A high-resolution photomicrograph of the chlorite schist from Stølsheimen is available at https://doi.org/10.6084/m9.figshare.c.3592064 .

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Many of our planet's "crises" were the result of sudden changes in plate tectonic 10! configuration or catastrophic outbursts of volcanism caused by mantle plume 11! impingement at the base of the lithosphere. At the Paleocene-Eocene boundary and in 12! the Early Eocene several mantle plumes, continental collision and mid-ocean ridge 13! subduction triggered a series of changes in seafloor spreading dynamics. We have 14! constructed a detailed global model of oceanic lithosphere age and spreading rates for 15! the 60 to 35 Ma interval. We revise evidence for changes in seafloor spreading 16! direction in the North Atlantic, Arctic and NE Pacific oceans. At least two periods of 17! spreading rate highs, which are separated by sharp value decrease, occurred along the 18! entire eastern North American plate boundary from C25 to C18 time (c. 57 to 40 Ma). 19! The collision and incipient subduction of the Early Eocene Siletzia oceanic LIP may 20! have caused the sharp decrease in spreading rate at C23 time in the Labrador Sea and 21! north of Charlie-Gibbs fracture zone. The post C23 rapid Farallon slab-break-off and 22! subsequent upper mantle flow upwelling may have led to further variations in North 23! Atlantic spreading rates at C22-21 time. Eastward Pacific subduction may have 24! resumed at c. 43 Ma as indicated by a steady NE Pacific seafloor-spreading regime 25! which resumed at or shortly after C21. The North Atlantic realm shows a delayed 26!response to tectonic events west of North America, with an increase in spreading rate 27! south of Charlie-Gibbs fracture zone from C20 to C18 time, followed by a steady 28! decrease until the Oligocene. North American Late Paleocene-Early Eocene 29! kimberlite magma that erupted more than 1000 km from its western plate boundary 30! constitutes additional evidence that tectonic stresses due to changes in the mantle-31! lithosphere interactions may have affected the entire plate, and therefore also its 32! eastern boundaries.