Evolution of young oceanic lithosphere and the meaning of seafloor subsidence rate

Abstract

Plate tectonics, a special class of mantle convection so far observed only on the Earth, is responsible for a vast array of geological processes, from the generation of continental crust to the modulation of atmospheric composition. Whereas conditions for its operation are still debated, the minimum requirement is generally thought that surface plates become denser than the underlying asthenosphere so that they can subduct. Recent studies, however, have raised the possibility that even mature oceanic plates remain buoyant because chemical buoyancy is too high to be overcome by negative thermal buoyancy, challenging the basic tenet of plate tectonics. Here we show that on the basis of new integrated geophysical and petrological modeling, oceanic plates do become negatively buoyant after ∼30 Myr. Our modeling also indicates that the seafloor would subside at a rate of ∼500 m Myr−1/2, which is considerably faster than the observed rate of ∼320 m Myr−1/2. We suggest that this discrepancy in subsidence rate is best explained by the combined effect of incomplete viscous relaxation within oceanic plates, radiogenic heat production in the convecting mantle, and the secular cooling of the Earth.

Geodynamics of divergent double subduction: 3‐D numerical modeling of a Cenozoic example in the Molucca Sea region, Indonesia

“…Alternatively, the observed plate convergence and arc‐arc collision in this region can be explained by self‐sustaining subduction of the Molucca Sea plate. Once subduction is initiated, a mature oceanic plate has sufficient negative buoyancy to maintain its subduction by the slab pull force [ Cloos , ; Korenaga and Korenaga , ]. Our results show that self‐consistent DDS can be solely achieved by slab pull and further leads to arc‐arc collision (e.g., Figures , and and Movie S1).…”

“…This drives the tectonic movement including convergence and final collision between the overriding plates. In general, density contrast between the oceanic lithosphere and the surrounding upper mantle increases due to thermal contraction and eclogitization of the basaltic crust [e.g., Cloos , ; Korenaga and Korenaga , ]. Here we run extra models modified based on reference model DDS_Ref to investigate the effect of negative buoyancy on DDS by using plate with variable density contrast Δ ρ = 40, 80 kg/m 3 with respect to that of the ambient upper mantle (DDS_Δρ40 and DDS_Δρ80; Table ).…”

“…For the top viscoplastic layer, von Mises yield criterion is employed with cohesion of 30 MPa and initial viscosity of 1000 × η um , and when yield occurs, the effective viscosity is replaced by where σ yield is the cohesive strength and is the second invariant of the deviatoric strain rate. The density of subducting plate is laterally uniform and is 40–80 kg/m 3 denser than the ambient upper mantle [ Cloos , ; Korenaga and Korenaga , ]. This structure mimics the nature of normal mature oceanic lithosphere, which becomes dense enough to subduct due to cooling and mineral phase transformation if the oceanic lithosphere is older than ~30 Myr [ Korenaga and Korenaga , ], facilitating subduction when the topmost viscoplastic layer yields and weakens.…”

“…The density of subducting plate is laterally uniform and is 40–80 kg/m 3 denser than the ambient upper mantle [ Cloos , ; Korenaga and Korenaga , ]. This structure mimics the nature of normal mature oceanic lithosphere, which becomes dense enough to subduct due to cooling and mineral phase transformation if the oceanic lithosphere is older than ~30 Myr [ Korenaga and Korenaga , ], facilitating subduction when the topmost viscoplastic layer yields and weakens. DDS is triggered by two bending tips of the presubducting plate at both sides (Figure ), each with initial lengthes of 150–200 km and dipping angles of 20°–30°, depending on configuration for specific models.…”

Reassessing the Thermal Structure of Oceanic Lithosphere With Revised Global Inventories of Basement Depths and Heat Flow Measurements

“…Their optimal model has a plate thickness of 106 km and a potential temperature of 1315 ∘ C. By including the temperature dependence of k, , and C P , McKenzie et al (2005) predicted that the seismogenic thickness of oceanic lithosphere approximately corresponds to the depth to the 600 ∘ C isothermal surface. More recently, increasingly sophisticated plate models that include lithostatic pressure, mineralogic phase transitions, and hydrothermal circulation within oceanic crust have also been developed (Afonso et al, 2007;Grose & Afonso, 2013;Korenaga & Korenaga, 2016;Schmeling et al, 2017; Figure 1c).…”