The dynamic life of an oceanic plate

Abstract

As the Earth's primary mode of planetary cooling, the oceanic plate is created at mid-ocean ridges, transported across the planet's surface, and destroyed at subduction zones. The evolution of its buoyancy and rheology during its lifespan maintains the coherence of the plate as a distinct geological entity and controls the localised deformation and vertical material exchange at plate boundaries, which enables the horizontal ocean-plate movements. These motions intimately link the oceanic plate to the overarching overturn of Earth's mantle: The plate forms out of rising mantle material at spreading ridges; it cools the Earth's interior as the cold thermal boundary layer to mantle convection; and its sinking portions drive not only the plate itself but also dominate global flow in the mantle. We scrutinise here the entire life cycle of the oceanic plate, starting with its birth at the mid-ocean ridge, including the thermal, rheological, and chemical conditions of initiation, followed by plate maturation as it ages and cools while crossing the seafloor, and finishing with the dynamics of plate destruction as it retires at the subduction zone to become a deeper part of Earth's convective system. We find that the full range of dynamic behaviour of the oceanic plate, including its forcing and overall framework within Earth's convecting system, is not fully captured by the existing concept of Plate Tectonics, which describes solely the horizontal surface kinematics of all plates. Therefore, we introduce a more specific and at the same time more integral concept named "Ocean-Plate Tectonics" that more specifically describes the dynamic life of the oceanic plate and accounts for the knowledge gained during the past fifty years. This "Ocean-Plate Tectonics" must have emerged on Earth at least 1 Billion years ago, and dominates Earth's dynamics today.

Pulsated Global Hydrogen and Methane Flux at Mid‐Ocean Ridges Driven by Pangea Breakup

“…The transition at 40 mm/a is important because this is the spreading rate above which MOR systems begin to transition between the cooler, amagmatic ridges dominated by tectonic accretion to warmer spreading regimes controlled by magmatic accretion (e.g., Canales et al, 2005; Dick et al, 2003; Small, 1994). This is supported by numerical modeling, which indicates that as spreading rates approach 40 mm/a, the thickness of oceanic crust is stabilized at 6–8 km (Crameri et al, 2019). Dick et al (2003) place the transition between slow and intermediate slightly higher, at 55 mm/a, we opt for a more conservative value for two reasons.…”

“…For our analysis we define spreading asymmetry as the distinct proportion of differing volumes of oceanic crust formed and preserved on each ridge flank integrated on a 1 Ma timescale. It occurs variably at all ridges, though appears more prominent at slow and ultraslow ridges (e.g., Crameri et al, 2019; Müller et al, 2008). At ridges spreading below 40 mm/a, asymmetry is as high as 60%, along segments of the Southwest Indian Ridge and Northern Mid‐Atlantic, though these appear to be outliers, with the cluster of data for slow and ultraslow ridge segments showing a mean that is much lower, between 10 and 20% asymmetry (Crameri et al, 2019).…”

“…It occurs variably at all ridges, though appears more prominent at slow and ultraslow ridges (e.g., Crameri et al, 2019; Müller et al, 2008). At ridges spreading below 40 mm/a, asymmetry is as high as 60%, along segments of the Southwest Indian Ridge and Northern Mid‐Atlantic, though these appear to be outliers, with the cluster of data for slow and ultraslow ridge segments showing a mean that is much lower, between 10 and 20% asymmetry (Crameri et al, 2019). In effect the increasing asymmetry with decreasing spreading rate is a function of the increasing proportion of tectonic accretion, at the cost of magmatic accretion, that occurs at ultraslow and slow spreading segments (e.g., Tucholke et al, 2008).…”

Tectonic Controls on Carbon and Serpentinite Storage in Subducted Upper Oceanic Lithosphere for the Past 320 Ma

“…In constructing bottom-up approaches to model volatile storage in oceanic lithosphere, we must consider a range of dependent and independent variables and the observational and analytical data that best constrain them (Crameri et al, 2019). Calculating estimates of carbon storage requires data constraining the: (i) thicknesses of each volcanic layer, (ii) proportion of peridotite exhumed into the upper oceanic lithosphere, (iii) degree of serpentinization, (iv) degree of basalt alteration, (v) bottom water temperature, and (vi) spreading rate.…”

“…The structure, composition, and potential volatile storage capacity of the oceanic lithosphere can be inferred as a function of the spreading rate of the ridge at which it formed. As the spreading rate varies both spatially and temporally (Müller et al, 2008;Crameri et al, 2019), the subduction of carbonates and water-rich serpentinites must also be allowed to vary spatially and temporally in any subduction flux model. The time-dependent storage capacity of oceanic lithosphere presents the second major challenge in a bottom-up approach.…”