Detachment tectonics at Mid-Atlantic Ridge 26°N.

ABSTRACT

Spreading processes associated with slow-spreading ridges are a complex interplay of volcanic accretion and tectonic dismemberment of the oceanic crust, resulting in an irregular seafloor morphology made up of blocks created by episodes of intense volcanic activity or tectonic deformation. These blocks undergo highly variable evolution, such as tilts or dissection by renewed tectonic extension, depending on their positions with respect to the spreading axis, core complexes, detachment or transform faults. Here, we use near-seafloor magnetic and bathymetric data and seismic profiles collected over the TAG Segment of the Mid-Atlantic Ridge to constrain the tectonic evolution of these blocks. Our study reveals that the presence and evolution of oceanic core complexes play a key role in triggering block movements. The deep subvertical detachment fault roots on the plate boundary, marked by a thermal anomaly and transient magma bodies. Thermal and magmatic variations control the structure and morphology of the seafloor above the subhorizontal detachment surface, occasionally leading to relocating the detachment.