The tectonic evolution of the Mid-Atlantic Ridge between 55°55'N and the Bight Transform Fault during the past 6 Ma

Abstract:

We present a new propagating rift model of the Mid-Atlantic Ridge between 55°55'N and the Bight Transform Fault (BTF) explaining the tectonic history of the area during the past 6 Ma, using marine magnetic anomalies collected in the fall of 2013. The data consist of thirteen flowline parallel lines across the ridge and they show that the accretion across the ridge has not been symmetric. Using Magellan, a new tool to model magnetic anomalies, we obtain a tectonic evolution of the area for the past 6 Ma. The area just south of the BTF (at 0-20 km distance) is characterized by a very large asymmetry in the magnetic data. This asymmetry is most clearly seen within the Brunhes anomaly, which has a big divide in it. Our model suggests that the ridge has shifted twice some 8-12 km to the east within the past 2 Ma resulting from two very rapid rift propagations. We could not determine whether the propagations were to the south or north because of very rapid propagation rates. The tectonic evolution of the area 20-90 km south of the BTF is simpler and the model is more readily understood. The model suggests that a few short lived propagators cause asymmetry in the area. They all, but one, propagate north toward the BTF and all, but one, transfer lithosphere from the Eurasian plate to the North-American plate. Unlike the prominent far reaching (> 100km) propagators just south of Iceland these propagators are short. They play an important role in the tectonic evolution of the ridge and our results suggest that the Mid-Atlantic Ridge in this area is very dynamic.