Dependencies of morphology and lithological variations on tectonics, thermal structure and ocean loading at ultra-slow and slow ridges.

Why do some mid-ocean ridges have morphology that expresses oceanic core complexes with large gabbro bodies, while others have smooth seafloors with large exposures of serpentinized mantle or rough seafloors, while lavas are observed almost everywhere?

Over the past few decades, numerical models have inferred that the fundamental mechanism controlling the wide diversity of lithology, crustal thickness, and ridge morphology is the balance between magmatism and tectonics. Key controls on this modeled equilibrium are the melt supply rate, which varies to account for the discontinuous volcanism observed on slow ridges, and the thermal structure, which depends on the balance between heat injected during magmatic accretion and heat removed by hydrothermal cooling, modulated by the spreading rate.

Based on this paradigm, it has been established that the fraction of melt that is accreted into the crust controls the formation of large oceanic core-complexes and flip-flop detachments, with the former being formed at fractions corresponding of half of spreading rate and the latter being formed when the melt supply is much smaller.

However, several fundamental questions remain poorly understood or unanswered. Why can slip on oceanic detachment faults continue and why does it stop? How do serpentinization and magmatic intrusions play a role in crustal growth and how do they interact? How and why do mechanisms related to magma supply switch from magmatic to detachment dominated mode during oceanic accretion?

Here we present self-consistent numerical simulations of the development of mid-ocean ridges, starting  from continental rifting and breakup. In our models melt supply varies dynamically with extension velocity and is affected by faulting. We focus on understanding how tectonism, melting, serpentinisation and hydrothermal cooling interact to form smooth-seafloor, core complexes and normal igneous seafloor, and their diverse crustal lithology.