Seafloor topography and the thermal budget of Earth

Korenaga, Jun

doi:10.1130/2015.2514(11)

Cited by 9 publications

(24 citation statements)

References 89 publications

(135 reference statements)

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“…In addition to using the plate model, which helps to explain the subsidence of old seafloor, Grose and Afonso [] reduced thermal expansivity to fit the subsidence of young seafloor. We do not adopt the plate model as it hinders our effort to understand seafloor subsidence in a dynamically meaningful manner [ Korenaga , ], and by the same token, we would like to identify physically plausible mechanisms that can explain the discrepancy between the predicted and observed subsidence rates. This will be discussed in the next section.…”

Section: Resultsmentioning

confidence: 99%

“…Seafloor subsidence can also be affected by a slight temperature gradient in the convecting mantle produced by radiogenic heat production [ Korenaga , ]. The amount of heat‐producing elements such as U and Th in the convecting mantle is very small, with the estimate of their total heat production being on the order of 1‐3×10 −12 W kg −1 (equivalent to 4–12 TW for the entire mantle) [ Jochum et al , ; Korenaga , ], which would lead to only <10 K increase over 100 Myr.…”

Section: Resultsmentioning

confidence: 99%

“…Whereas some numerical studies suggest younger seafloor ages for the onset of sublithospheric, small‐scale convection [e.g., Buck and Parmentier , ; Dumoulin et al , ; Zlotnik et al , ], the onset time depends critically on the rheology of the upper mantle [ Korenaga and Jordan , ], our understanding of which is still limited [ Korenaga and Karato , ; Mullet et al , ]. Although there is a considerable time lag between the onset of sublithospheric convection and its manifestation in surface heat flow [ Korenaga , ], the onset of convection would be immediately reflected in surface topography even with realistic mantle rheology [ Korenaga , ]. As the global depth‐age relation of seafloor does not exhibit notable deviations from the half‐space cooling trend up to 70 Ma [ Parsons and Sclater , ; Stein and Stein , ; Korenaga and Korenaga , ], the possibility of convective instability can be excluded when modeling the global behavior of young oceanic lithosphere.…”

Section: Numerical Modeling Of Thermal Evolutionmentioning

confidence: 99%

“…The observed subsidence rate of ∼320 m Myr −1/2 [ Korenaga and Korenaga , ], however, appears to be too low to be explained by the thermal expansivity of mantle minerals [ Korenaga , ; Grose and Afonso , ], presenting another challenge for our theoretical understanding of the evolution of suboceanic mantle. Two disparate mechanisms have been put forward to explain this discrepancy: reduction in effective thermal expansivity caused by incomplete viscous relaxation within oceanic lithosphere [ Korenaga , ] and dynamic topography caused by radiogenic heat production in the sublithospheric mantle [ Korenaga , ]. It is currently unresolved which mechanism is more important.…”

Section: Introductionmentioning

confidence: 99%

“…In this paper, we model thermal evolution for the duration of 100 Myr and focus on the first ∼70 Myr. Seafloor older than ∼70 Myr old is known to deviate from the prediction of simple half‐space cooling [ Parsons and Sclater , ; Stein and Stein , ], and such deviation can be explained by, for example, the occurrence of small‐scale convection [ Huang and Zhong , ; Korenaga , ]. Here we restrict ourselves to the simple, early phase of lithospheric evolution.…”

Section: Introductionmentioning

confidence: 99%

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

Korenaga

2016

JGR Solid Earth

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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.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Numerical Modeling Of Thermal Evolutionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Korenaga

2016

JGR Solid Earth

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Imaging Pacific lithosphere seismic discontinuities—Insights from SS precursor modeling

et al. 2017

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Oceanic lithosphere provides an ideal location to decipher the nature of the lithosphere‐asthenosphere system which is vital to our understanding of plate tectonics. It is well established that oceanic lithosphere cools, thickens, and subsides as it ages according to the conductive cooling models. Yet this simple realization fails to explain various observations. For example, old oceanic lithosphere does not subside as predicted. Further, precise imaging of the lower boundary of the oceanic lithosphere has proven challenging. Here we use SS precursors to image the discontinuity structure across the Pacific Ocean using 24 years of teleseismic data. We image a sharp pervasive velocity discontinuity (3–15% drop over <21 km) at 30–80 km depth that increases in depth with age from the ridge to at least 36 ± 9 Myr along the 1100°C conductive cooling isotherm. Beneath seafloor >36 Myr, there is no age‐depth dependence, and we image the discontinuity at an average depth of 60 ± 1.5 km. The amplitude and sharpness of the boundary suggests that a compositional variation and/or layered carbonatitic melt may be required to explain our observations rather than temperature alone. The strength and pervasiveness of the boundary suggest that it is likely related to the lithosphere‐asthenosphere boundary. An additional deeper discontinuity at 80–120 km depth is imaged intermittently that in most cases likely represents a continuing negative velocity gradient in depth.

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