Causes and Consequences of Diachronous V-Shaped Ridges in the North Atlantic Ocean

In the North Atlantic Ocean, the geometry of diachronous V-shaped
features that straddle the Reykjanes Ridge is often attributed to thermal
pulses which advect away from the center of the Iceland plume. Recently,
two alternative hypotheses have been proposed: rift propagation and buoyant
mantle upwelling. Here, we evaluate these different proposals using basinwide
geophysical and geochemical observations. The centerpiece of our analysis
is a pair of seismic reflection profiles oriented parallel to flowlines that
span the North Atlantic Ocean. V-shaped ridges and troughs are mapped
on both Neogene and Paleogene oceanic crust, enabling a detailed chronology
of activity to be established for the last 50 million years. Estimates of
the cumulative horizontal displacement across normal faults help to discriminate
between brittle and magmatic modes of plate separation, suggesting
that crustal architecture is sensitive to the changing planform of the plume.
Water-loaded residual depth measurements are used to estimate crustal thickness
and to infer mantle potential temperature which varies by ±25◦C on
timescales of 3–8 Ma. This variation is consistent with the range of temperatures
inferred from geochemical modeling of dredged basaltic rocks along
the ridge axis itself, from changes in Neogene deep-water circulation, and from the regional record of episodic Cenozoic magmatism. We conclude that radial
propagation of transient thermal anomalies within an asthenospheric channel
that is 150 ± 50 km thick best accounts for the available geophysical
and geochemical observations.