Generation and evolution of the oceanic lithosphere in the North Atlantic

Half a century ago, our view of the Earth shifted from that of a Planet with fixed continents and ancient stable ocean basins to one with wandering continents and young,
active ocean basins, reviving Wegener’s Continental Drift that had rested dormant for
years. The lithosphere is the external, mostly solid and relatively rigid layer of the
Earth, with thickness and composition different below the oceans and within the continents. We will review the processes leading to the generation and evolution of the
Earth’s lithosphere that lies beneath the oceans. We will discuss how the oceanic lithosphere is generated along mid-ocean ridges due to upwelling of convecting hot mantle.
We will consider in particular lithosphere generation occurring along the northern Mid
Atlantic Ridge (MAR) from Iceland to the equator, including the formation of transform offsets. We will then focus on the Vema fracture zone at 10°–11° N, where a
~ 300 km long uplifted and exposed sliver of lithosphere allows to reconstruct the
evolution of lithosphere generation at a segment of the MAR from 25 million years
ago to the Present. This axial ridge segment formed 50 million years ago, and reaches
today 80 km in length. The degree of melting of the subridge mantle increased from
16 million years ago to today, although with some oscillations. The mantle presently
upwelling beneath the MAR becomes colder and/or less fertile going from Iceland to
the Equator, with “waves” of hot/fertile mantle migrating southwards from the Azores
plume. Scientific revolutions seem to occur periodically in the history of Science; we
wonder when the next revolution will take place in the Earth Science, and to what
extent our present views will have to be modified