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Article Dans Une Revue Earth and Planetary Science Letters Année : 2020

Controls on the magmatic fraction of extension at mid-ocean ridges

Jean-Arthur Olive
Pierre Dublanchet

Résumé

The fraction M of plate separation accommodated by magma emplacement at mid-ocean ridges has been recognized as the main control on seafloor spreading modes, yet the factors that control M itself are poorly understood. Here we put forward a simple theoretical framework explaining M in terms of short-term cycles of earthquakes and dike intrusions interacting with one another by modulating the stress state of the ridge axis. Axial lithospheric thickness and the rate of pressure build-up in shallow, replenishing magma sills are the two main parameters controlling M in our simulations. Combined with plausible scenarios for the increase of pressure build-up rate and the decrease of lithospheric thickness with increasing spreading rate, our model appropriately brackets available measurements of M from slow, intermediate, and fast-spreading ridges. Our model further suggests that the transitions between major modes of seafloor spreading (detachment faulting, symmetric faulting, and fully-magmatic) correspond to thresholds in axial lithospheric thickness, and that the great variability in M at slow and ultraslow ridges directly reflects along-axis variability in thermal structure. More generally, this implies that the balance between bottom-up magmatic heating and top-down hydrothermal cooling fully determines the time-averaged rate of magmatic intrusions in the brittle lithosphere, and thus the modes of mid-ocean ridge faulting which shape ∼2/3 of Earth's surface.
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Dates et versions

hal-02921482 , version 1 (25-08-2020)

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Jean-Arthur Olive, Pierre Dublanchet. Controls on the magmatic fraction of extension at mid-ocean ridges. Earth and Planetary Science Letters, 2020, 549, pp.116541. ⟨10.1016/j.epsl.2020.116541⟩. ⟨hal-02921482⟩
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