Along-strike magma-poor/magma-rich spreading transitions


 1D/2D data-based studies of active spreading centers brought the knowledge of extension rate-dependent stretching-dominated versus buoyancy-dominated spreading. 3D reflection seismic data from the extinct center of an initial oceanic corridor in the Caribbean allow us to see an along-strike transition between stretching- and buoyancy-dominated spreading where the spreading through detachment faulting is a precursor to the magma-assisted spreading. Studying progressively more evolved portions of the spreading center, going from its end towards its center, we see a progressively higher ascent of the asthenosphere, which heats the developing core complex in the exhuming footwall of the initial stretching-dominated system. The asthenospheric ascent is associated with thermal weakening of the core complex, which eventually results in ductile deformation reaching the upper portion of the complex. Subsequently, the core complex is penetrated by the dyke located at the top of the asthenospheric body. The dyke, which subsequently evolves to diapir-shaped body, reaches the sea floor and establishes a magma-assisted steady-state seafloor spreading. These observations lead to a model explaining the initiation of the magma-assisted spreading in the initial oceanic corridor. Furthermore, they also improve our knowledge of multiple interacting mechanisms involved in the breakup of the last continental lithospheric layer, subsequent disorganized spreading and younger organized spreading.
 
 Supplementary material at
 https://doi.org/10.6084/m9.figshare.c.6332993
