The Experts below are selected from a list of 267 Experts worldwide ranked by ideXlab platform
Jun Korenaga - One of the best experts on this subject based on the ideXlab platform.
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on the yield strength of Oceanic Lithosphere
Geophysical Research Letters, 2017Co-Authors: Chhavi Jain, Jun Korenaga, Shun-ichiro KaratoAbstract:The yield strength of Oceanic Lithosphere determines the mode of mantle convection in a terrestrial planet, and low-temperature plasticity in olivine aggregates is generally believed to govern the plastic rheology of the stiffest part of Lithosphere. Because, so far, proposed flow laws for this mechanism exhibit nontrivial discrepancies, we revisit the recent high-pressure deformation data of Mei et al. (2010) with a comprehensive inversion approach based on Markov chain Monte Carlo sampling. Our inversion results indicate that the uncertainty of the relevant flow law parameters is considerably greater than previously thought. Depending on the choice of flow law parameters, the strength of Oceanic Lithosphere would vary substantially, carrying different implications for the origin of plate tectonics on Earth. To reduce the flow law ambiguity, we suggest that it is important to establish a theoretical basis for estimating macroscopic stress in high-pressure experiments and also to better utilize marine geophysical observations.
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macroscopic strength of Oceanic Lithosphere revealed by ubiquitous fracture zone instabilities
Earth and Planetary Science Letters, 2016Co-Authors: Cecilia Cadio, Jun KorenagaAbstract:The origin of plate tectonics is one of the most fundamental issues in earth and planetary sciences. Laboratory experiments indicate that the viscosity of silicate rocks is so strongly temperature-dependent that the entire surface of the Earth should be one immobile rigid plate. The rheology of Oceanic Lithosphere is, however, still poorly understood, and there exist few constraints on the temperature dependency of viscosity on the field scale. Here we report a new kind of observational constraint based on the geoid along Oceanic fracture zones. We identify a large number of conspicuous small-scale geoid anomalies, which cannot be explained by the standard evolution model of Oceanic Lithosphere, and estimate their source density perturbations using a new Bayesian inversion method. Our results suggest that they are caused most likely by small-scale convection involving temperature perturbations of ∼300 K±100 K. Such thermal contrast requires the activation energy of mantle viscosity to be as low as 100±50 kJmol−1 in case of diffusion creep, and 225±112 kJmol−1 in case of dislocation creep, substantially reducing the thickness of the stiffest part of Oceanic Lithosphere. Oceanic Lithosphere may thus be broken and bent much more easily than previously thought, facilitating the operation of plate tectonics.
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localization of geoid anomalies and the evolution of Oceanic Lithosphere a case study from the mendocino fracture zone
Journal of Geophysical Research, 2012Co-Authors: Cecilia Cadio, Jun KorenagaAbstract:[1] The thermal evolution of Oceanic Lithosphere is investigated by focusing on geoid offsets occurring across the Mendocino Fracture Zone, where plates with different ages are juxtaposed. Various processing techniques have been devoted to separate the geoid signal of the age contrast from regional and shorter wavelength components unrelated to the thermal structure of Lithosphere. Nevertheless, due to processing differences, estimates of geoid offsets vary, and no agreement on the thermal evolution of Oceanic Lithosphere has been found so far. In this study, we propose to use a continuous wavelet analysis to accurately characterize the components of the geoid at different spatial scales and to estimate a new geoid slope-age relationship from localized signals. We also apply the same wavelet transform on a set of synthetic geoid calculated with different assumptions on plate cooling. The comparison of the observed geoid offsets with those predicted from cooling models indicates that our approach can successfully remove unwanted regional contributions and isolate the geoid signature due to lithospheric cooling. Our results suggest that, contrary to previous studies, geoid slopes measured at the Mendocino Fracture Zone are compatible with both the half-space cooling model and the plate model.
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subsidence of normal Oceanic Lithosphere apparent thermal expansivity and seafloor flattening
Earth and Planetary Science Letters, 2008Co-Authors: Tomoko Korenaga, Jun KorenagaAbstract:Abstract Seafloor topography has been a key observational constraint on the thermal evolution of Oceanic Lithosphere, which is the top boundary layer of convection in Earth's mantle. At least for the first ~ 70 Myr, the age progression of seafloor depth is known to follow the prediction of half-space cooling, and the subsidence rate is commonly believed to be ~ 350 m Ma − 1/2 . Here we show that, based on a new statistical analysis of global bathymetry, the average subsidence rate of normal Oceanic Lithosphere is likely to be ~ 320 m Ma − 1/2 , i.e., ~ 10% lower than the conventional value. We define the ‘normal’ seafloor as regions uncorrelated with anomalous crust such as hotspots and Oceanic plateaus, but the lower subsidence rate appears to be a stable estimate, not depending on how exactly we define the normal seafloor. This low subsidence rate can still be explained by half-space cooling with realistic mantle properties, if the effective thermal expansivity of a viscoelastic mantle is taken into account. In light of a revised model of half-space cooling, the normal seafloor unperturbed by the emplacement of anomalous crust exists for all ages, and the so-called seafloor flattening seems to be mostly caused by hotspots and Oceanic plateaus.
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effective thermal expansivity of maxwellian Oceanic Lithosphere
Earth and Planetary Science Letters, 2007Co-Authors: Jun KorenagaAbstract:Abstract The thermal expansivity of Oceanic Lithosphere is a key mineral physics parameter that controls the rate of seafloor subsidence. Because of strongly temperature-dependent mantle rheology, effective expansivity for Lithosphere as a whole could be substantially lower than indicated by mineral physics data. Viscoelastic modeling indicates that this reduction in expansivity could be as high as ∼ 15–30% for a plausible range of mantle viscosity. Though brittle relaxation by thermal cracking is likely to alleviate this reduction, tension cracking results in fractured Lithosphere with finite crack porosity, thereby prohibiting the recovery of fully equilibrated density. Even with complete brittle relaxation, effective thermal expansivity could still be lower by up to ∼ 20%.
Juan Carlos Afonso - One of the best experts on this subject based on the ideXlab platform.
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Comprehensive plate models for the thermal evolution of Oceanic Lithosphere
Geochemistry Geophysics Geosystems, 2013Co-Authors: Christopher J Grose, Juan Carlos AfonsoAbstract:[1] Seafloor spreading and the cooling of Oceanic Lithosphere is a fundamental feature of plate tectonics in the Earth, the details of which are unveiled by modeling with constraints from mineral physics and geophysical observations. To work toward a more complete model of the thermal evolution of Oceanic Lithosphere, we investigate the contributions of axial hydrothermal circulation, Oceanic crust, and temperature-pressure-dependent thermal properties. We find that models with only temperature-dependent properties disagree with geophysical observations unless properties are artificially modified. On the other hand, more comprehensive models are in better agreement with geophysical observations. Our preferred model requires a thermal expansivity reduction of 15% from a mineral physics estimate, and predicts a plate thickness of about 110–130 km. A principal result of our analysis is that the Oceanic crust is a major contributor to the cooling of Oceanic Lithosphere. The Oceanic crust acts as an insulating lid on the mantle, causing the rate of lithospheric cooling to increase from “crustal” values near the ridge to higher mantle values at old-age. Major consequences of this insulation effect are: (a) low seafloor subsidence rate in proximity to ridge axes (
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comprehensive plate models for the thermal evolution of Oceanic Lithosphere
Geochemistry Geophysics Geosystems, 2013Co-Authors: Christopher J Grose, Juan Carlos AfonsoAbstract:[1] Seafloor spreading and the cooling of Oceanic Lithosphere is a fundamental feature of plate tectonics in the Earth, the details of which are unveiled by modeling with constraints from mineral physics and geophysical observations. To work toward a more complete model of the thermal evolution of Oceanic Lithosphere, we investigate the contributions of axial hydrothermal circulation, Oceanic crust, and temperature-pressure-dependent thermal properties. We find that models with only temperature-dependent properties disagree with geophysical observations unless properties are artificially modified. On the other hand, more comprehensive models are in better agreement with geophysical observations. Our preferred model requires a thermal expansivity reduction of 15% from a mineral physics estimate, and predicts a plate thickness of about 110–130 km. A principal result of our analysis is that the Oceanic crust is a major contributor to the cooling of Oceanic Lithosphere. The Oceanic crust acts as an insulating lid on the mantle, causing the rate of lithospheric cooling to increase from “crustal” values near the ridge to higher mantle values at old-age. Major consequences of this insulation effect are: (a) low seafloor subsidence rate in proximity to ridge axes (<5 Ma), (b) the thermal structure of Oceanic Lithosphere is significantly warmer than previous models, (c) seafloor heat flow is significantly lower over young (<35 Ma) seafloor compared to simple models, (d) a low net seafloor heat flux (∼27 TW), and (e) temperature at the base of the seismogenic zone extends to 700–800°C mantle.
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Effects of compositional and rheological stratifications on small‐scale convection under the oceans: Implications for the thickness of Oceanic Lithosphere and seafloor flattening
Geophysical Research Letters, 2008Co-Authors: Juan Carlos Afonso, Sergio Zlotnik, Manel FernandezAbstract:[1] Pressure-release melting at mid-ocean ridges generate compositional and rheological layering in the Oceanic mantle that may control the evolution of the Oceanic Lithosphere. We use dynamic models coupled with melting and petrological models to explore 1) the influence of this layering on the development of small-scale convection under the oceans, 2) its role in determining the thickness of Oceanic Lithosphere, and 3) its feasibility as responsible for the deviations of seafloor and surface heat flow from predictions by conductive models in mature Oceanic Lithosphere. Here we show that the existence of small-scale convection is entirely compatible with experimental creep parameters and flow laws, and that the viscosity stratification due to melt extraction (i.e., H2O removal) is the main factor controlling the plate's thermal evolution, its asymptotic thickness, and the flattening of seafloor and surface heat flow at ages ≳70 Ma. The effects of Al-rich phase transitions and compositional layering are minor.
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effects of compositional and rheological stratifications on small scale convection under the oceans implications for the thickness of Oceanic Lithosphere and seafloor flattening
Geophysical Research Letters, 2008Co-Authors: Juan Carlos Afonso, Sergio Zlotnik, Manel FernandezAbstract:[1] Pressure-release melting at mid-ocean ridges generate compositional and rheological layering in the Oceanic mantle that may control the evolution of the Oceanic Lithosphere. We use dynamic models coupled with melting and petrological models to explore 1) the influence of this layering on the development of small-scale convection under the oceans, 2) its role in determining the thickness of Oceanic Lithosphere, and 3) its feasibility as responsible for the deviations of seafloor and surface heat flow from predictions by conductive models in mature Oceanic Lithosphere. Here we show that the existence of small-scale convection is entirely compatible with experimental creep parameters and flow laws, and that the viscosity stratification due to melt extraction (i.e., H2O removal) is the main factor controlling the plate's thermal evolution, its asymptotic thickness, and the flattening of seafloor and surface heat flow at ages ≳70 Ma. The effects of Al-rich phase transitions and compositional layering are minor.
Azusa Shito - One of the best experts on this subject based on the ideXlab platform.
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evolution of the Oceanic Lithosphere inferred from po so waves traveling in the philippine sea plate
Journal of Geophysical Research, 2015Co-Authors: Azusa Shito, Daisuke Suetsugu, Takashi FurumuraAbstract:Po/So waves are characterized by their high-frequency content and long-duration travel over great distances (up to 3000 km) through the Oceanic Lithosphere. Po/So waves are developed by the multiple forward scattering of P- and S-waves due to small-scale stochastic random heterogeneities. To study the nature of these heterogeneities, Po/So waves are analyzed in the Philippine Sea Plate, which consists of three regions with different lithospheric ages. In the Philippine Sea Plate, Po/So waves propagate in the youngest region (15 Ma) and propagate more effectively in older regions. We investigate the mechanism of this propagation efficiency using numerical Finite Difference Method simulations of 2-D seismic wave propagation. The results of this study demonstrate that the increase in propagation efficiency of Po/So waves depends on the age of the Oceanic Lithosphere, and this relationship can be qualitatively explained by thickening of the Oceanic Lithosphere including small-scale heterogeneities and a reduction in the intrinsic attenuation. These small-scale heterogeneities may form continuously in Oceanic Lithosphere from the time of its formation at a spreading ridge, via the solidification of melts distributed in the asthenosphere.
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small scale heterogeneities in the Oceanic Lithosphere inferred from guided waves
Geophysical Research Letters, 2013Co-Authors: Azusa Shito, Daisuke Suetsugu, Takashi Furumura, Hiroko SugiokaAbstract:[1] We analyze seismic waveforms from deep-focus earthquakes occurring in the subducting slab beneath Japan, recorded by broadband ocean bottom seismometers (BBOBSs) installed on the northwestern Pacific Ocean seafloor. The data reveal waveforms with a low-frequency direct P onset, followed by large-amplitude, high-frequency, long-duration Po and So waves. From the analysis of the BBOBS records and a numerical finite-difference method simulation of seismic wave propagation, we elucidate the generation and propagation processes of such guided waves. We demonstrate that the low-frequency direct P and S waves propagate in the asthenosphere and that the following high-frequency, long-duration Po and So waves are developed by multiple forward scattering of P and S waves. The scattering occurs due to laterally elongated heterogeneities in both the subducting and horizontal parts of the Oceanic Lithosphere, with the apparent velocities (Vp = 8.1 km/s, Vs = 4.6 km/s) being close to the velocities of Oceanic Lithosphere.
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Small‐scale heterogeneities in the Oceanic Lithosphere inferred from guided waves
Geophysical Research Letters, 2013Co-Authors: Azusa Shito, Daisuke Suetsugu, Takashi Furumura, Hiroko SugiokaAbstract:[1] We analyze seismic waveforms from deep-focus earthquakes occurring in the subducting slab beneath Japan, recorded by broadband ocean bottom seismometers (BBOBSs) installed on the northwestern Pacific Ocean seafloor. The data reveal waveforms with a low-frequency direct P onset, followed by large-amplitude, high-frequency, long-duration Po and So waves. From the analysis of the BBOBS records and a numerical finite-difference method simulation of seismic wave propagation, we elucidate the generation and propagation processes of such guided waves. We demonstrate that the low-frequency direct P and S waves propagate in the asthenosphere and that the following high-frequency, long-duration Po and So waves are developed by multiple forward scattering of P and S waves. The scattering occurs due to laterally elongated heterogeneities in both the subducting and horizontal parts of the Oceanic Lithosphere, with the apparent velocities (Vp = 8.1 km/s, Vs = 4.6 km/s) being close to the velocities of Oceanic Lithosphere.
Manel Fernandez - One of the best experts on this subject based on the ideXlab platform.
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Effects of compositional and rheological stratifications on small‐scale convection under the oceans: Implications for the thickness of Oceanic Lithosphere and seafloor flattening
Geophysical Research Letters, 2008Co-Authors: Juan Carlos Afonso, Sergio Zlotnik, Manel FernandezAbstract:[1] Pressure-release melting at mid-ocean ridges generate compositional and rheological layering in the Oceanic mantle that may control the evolution of the Oceanic Lithosphere. We use dynamic models coupled with melting and petrological models to explore 1) the influence of this layering on the development of small-scale convection under the oceans, 2) its role in determining the thickness of Oceanic Lithosphere, and 3) its feasibility as responsible for the deviations of seafloor and surface heat flow from predictions by conductive models in mature Oceanic Lithosphere. Here we show that the existence of small-scale convection is entirely compatible with experimental creep parameters and flow laws, and that the viscosity stratification due to melt extraction (i.e., H2O removal) is the main factor controlling the plate's thermal evolution, its asymptotic thickness, and the flattening of seafloor and surface heat flow at ages ≳70 Ma. The effects of Al-rich phase transitions and compositional layering are minor.
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effects of compositional and rheological stratifications on small scale convection under the oceans implications for the thickness of Oceanic Lithosphere and seafloor flattening
Geophysical Research Letters, 2008Co-Authors: Juan Carlos Afonso, Sergio Zlotnik, Manel FernandezAbstract:[1] Pressure-release melting at mid-ocean ridges generate compositional and rheological layering in the Oceanic mantle that may control the evolution of the Oceanic Lithosphere. We use dynamic models coupled with melting and petrological models to explore 1) the influence of this layering on the development of small-scale convection under the oceans, 2) its role in determining the thickness of Oceanic Lithosphere, and 3) its feasibility as responsible for the deviations of seafloor and surface heat flow from predictions by conductive models in mature Oceanic Lithosphere. Here we show that the existence of small-scale convection is entirely compatible with experimental creep parameters and flow laws, and that the viscosity stratification due to melt extraction (i.e., H2O removal) is the main factor controlling the plate's thermal evolution, its asymptotic thickness, and the flattening of seafloor and surface heat flow at ages ≳70 Ma. The effects of Al-rich phase transitions and compositional layering are minor.
Takashi Furumura - One of the best experts on this subject based on the ideXlab platform.
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evolution of the Oceanic Lithosphere inferred from po so waves traveling in the philippine sea plate
Journal of Geophysical Research, 2015Co-Authors: Azusa Shito, Daisuke Suetsugu, Takashi FurumuraAbstract:Po/So waves are characterized by their high-frequency content and long-duration travel over great distances (up to 3000 km) through the Oceanic Lithosphere. Po/So waves are developed by the multiple forward scattering of P- and S-waves due to small-scale stochastic random heterogeneities. To study the nature of these heterogeneities, Po/So waves are analyzed in the Philippine Sea Plate, which consists of three regions with different lithospheric ages. In the Philippine Sea Plate, Po/So waves propagate in the youngest region (15 Ma) and propagate more effectively in older regions. We investigate the mechanism of this propagation efficiency using numerical Finite Difference Method simulations of 2-D seismic wave propagation. The results of this study demonstrate that the increase in propagation efficiency of Po/So waves depends on the age of the Oceanic Lithosphere, and this relationship can be qualitatively explained by thickening of the Oceanic Lithosphere including small-scale heterogeneities and a reduction in the intrinsic attenuation. These small-scale heterogeneities may form continuously in Oceanic Lithosphere from the time of its formation at a spreading ridge, via the solidification of melts distributed in the asthenosphere.
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small scale heterogeneities in the Oceanic Lithosphere inferred from guided waves
Geophysical Research Letters, 2013Co-Authors: Azusa Shito, Daisuke Suetsugu, Takashi Furumura, Hiroko SugiokaAbstract:[1] We analyze seismic waveforms from deep-focus earthquakes occurring in the subducting slab beneath Japan, recorded by broadband ocean bottom seismometers (BBOBSs) installed on the northwestern Pacific Ocean seafloor. The data reveal waveforms with a low-frequency direct P onset, followed by large-amplitude, high-frequency, long-duration Po and So waves. From the analysis of the BBOBS records and a numerical finite-difference method simulation of seismic wave propagation, we elucidate the generation and propagation processes of such guided waves. We demonstrate that the low-frequency direct P and S waves propagate in the asthenosphere and that the following high-frequency, long-duration Po and So waves are developed by multiple forward scattering of P and S waves. The scattering occurs due to laterally elongated heterogeneities in both the subducting and horizontal parts of the Oceanic Lithosphere, with the apparent velocities (Vp = 8.1 km/s, Vs = 4.6 km/s) being close to the velocities of Oceanic Lithosphere.
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Small‐scale heterogeneities in the Oceanic Lithosphere inferred from guided waves
Geophysical Research Letters, 2013Co-Authors: Azusa Shito, Daisuke Suetsugu, Takashi Furumura, Hiroko SugiokaAbstract:[1] We analyze seismic waveforms from deep-focus earthquakes occurring in the subducting slab beneath Japan, recorded by broadband ocean bottom seismometers (BBOBSs) installed on the northwestern Pacific Ocean seafloor. The data reveal waveforms with a low-frequency direct P onset, followed by large-amplitude, high-frequency, long-duration Po and So waves. From the analysis of the BBOBS records and a numerical finite-difference method simulation of seismic wave propagation, we elucidate the generation and propagation processes of such guided waves. We demonstrate that the low-frequency direct P and S waves propagate in the asthenosphere and that the following high-frequency, long-duration Po and So waves are developed by multiple forward scattering of P and S waves. The scattering occurs due to laterally elongated heterogeneities in both the subducting and horizontal parts of the Oceanic Lithosphere, with the apparent velocities (Vp = 8.1 km/s, Vs = 4.6 km/s) being close to the velocities of Oceanic Lithosphere.