Global Eocene tectonic unrest: Possible causes and effects around the North American plate

摘要

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