Mantle Convection Research Articles

The Upper Mantle Geoid for Lithospheric Structure and Dynamics

AbstractGeoid anomalies offer crucial information on the internal density structure of the Earth, and thus, on its constitution and dynamic state. In order to interpret geoid undulations in terms of depth, magnitude and lateral extension of density anomalies in the lithosphere and upper mantle, the effects of lower mantle density anomalies need to be removed from the full geoid (thus obtaining the residual “upper mantle geoid”). However, how to achieve this seemingly simple filtering exercise has eluded consensus for decades in the solid Earth community. While there is wide agreement regarding the causative masses of degrees >10 in spherical harmonic expansions of the upper mantle geoid, those contributing to degrees <7–8 remain ambiguous. Here we use spherical harmonic analysis and recent tomography and density models from joint seismic‐geodynamic inversions to derive a representative upper mantle geoid, including the contributions from low harmonic degrees. We show that the upper mantle geoid contains important contributions from degrees 5 and 6 and interpret the causative masses as arising from the coupling between the long‐wavelength lithospheric structure and the sublithospheric upper mantle convection pattern. Importantly, the contributions from degrees 3 < l < 8 do not show a simple power‐law behavior (e.g., Kaula's rule), which precludes the use of standard filtering techniques in the spectral domain. Our upper mantle geoid model will be useful in studies of (a) lithospheric structure, (b) dynamic topography and mantle viscosity, (c) lithosphere‐asthenosphere interactions and (d) the global stress field within the lithosphere and its associated hazards.

Novel High‐Pressure Potassium Chloride Monohydrate and Its Implications for Water‐Rich Planetary Bodies

AbstractSaline water is a common fluid on the Earth‘s surface and in ice planets. Potassium chloride (KCl) is a common salt and is expected to be a ubiquitous solute in salt water in the Universe; however, few studies investigated the behavior of KCl‐H2O system at high pressures and temperatures. In this study, powder and single‐crystal X‐ray diffraction (SC‐XRD), Raman and Brillouin scattering combined with diamond anvil cells were used to investigate the phase relation in the KCl‐H2O system for different KCl concentrations at 0–4 GPa and 298–405 K. The results of powder X‐ray diffraction and Raman scattering demonstrate that a novel KCl hydrate is formed when KCl aqueous solutions transform to solid ice‐VI and ice‐VII at high pressure. Simultaneously, the single‐crystal of KCl hydrate is synthesized from a supersaturated KCl solution at 298 K and 1.8 GPa. The structure is solved by SC‐XRD, indicating a KCl monohydrate with the P21/n space group is formed. We have verified the phase stability of KCl monohydrate by using Raman spectroscopy and density functional theory. Our results indicate that KCl monohydrate is a stable phase under pressure and temperature conditions between 1.6 and 2.4 GPa and 298–359 K. By considering the thermal profile and composition of icy moons, we hypothesize that the formation and decomposition of KCl monohydrate might induce mantle convection in these moons.

P and S Wave Anisotropic Tomography of the Banda Subduction Zone

AbstractIn subduction zones with slab‐slab interactions, the pattern of mantle convection is very complex and still unclear. In this study, we jointly invert a large number of P and S wave arrival time data of local earthquakes for 3‐D isotropic and anisotropic velocity structures of the Banda subduction zone. Along the curved Banda arc, the subducting Indo‐Australian slab is detected clearly as a high‐velocity zone, and its azimuthal anisotropy changes along the arc strike, representing fossil anisotropy within the slab and modified anisotropy by the subduction processes. Around the northern edge of the Banda slab, a semi‐toroidal pattern of anisotropy appears in low‐velocity anomalies, representing mantle flow extruded from the Banda arc and escaped from a gap of the Banda‐Molucca slab toward the northeast. Our 3‐D anisotropic tomography uncovers the mantle convection pattern induced by the slab‐slab interactions, shedding new light on the complex dynamical processes in this curved subduction zone.

Asymmetry and evolution of craton-influenced rifted margins

Abstract Rifting can result in asymmetric conjugate margins. In numerical models with laterally homogeneous lithosphere, the polarity of the asymmetry is random and results from spontaneous strain localization on a dominant fault/shear zone. However, along the central South Atlantic, margin width is well correlated to the proximity of the rift to a craton during rifting. To understand the evolution of rifting close to a craton, we used numerical experiments that included a thick craton lithosphere adjacent to a thinner, mobile-belt lithosphere. When rifting starts close to the craton, i.e., ≤ 100 km, deformation focuses along a fault/shear zone dipping toward the craton, leading to cratonward asymmetric asthenospheric uplift and rift migration. This results in a narrow margin on the craton side and a wide margin on the mobile-belt side. Craton-related asymmetry results in the wide margin subsiding more than the narrow one, inducing the formation of large synrift sag basins in the wide conjugate, as in the South Atlantic. This differential subsidence is preserved for ~100 m.y. after breakup and may partly explain the present-day higher dynamic topography close to cratons in the central South Atlantic. Mantle flow during asymmetric rifting leads to weakening of the craton lithosphere, partial intermixing, and recycling into the convective mantle, as interpreted for this sector of the South Atlantic ridge. Thus, rifting adjacent to a craton may have wide-ranging tectonic, stratigraphic, and compositional consequences that affect not only margin architecture, but also the development of subsequent dynamic topography and the spreading system.

Mantle convection and diamonds

Research subject. The present evolutionary stage of geodynamic theory is associated with the idea of thermochemical convection of various levels in the Earth's mantle, where the centrifugal branches are represented by plumes, and the centripetal - by subduction zones. Aim. The study of diamonds contributes to an understanding of when, at what level in mantle, under what P-T conditions and geochemical environment particular diamonds originated, which were then transported by centrifugal convection flows to the Earth's surface, thereby permitting characterization of this flow. Materials and methods. Generalization of published materials and characterization of mineral inclusions in diamonds allow the general structure of mantle convection to be clarified in different epochs and different regions. Results. The data obtained on mineral inclusions in diamonds, along with the experimental data on the P-T conditions of their mineral parageneses and geophysical data on mantle properties, indicate that the depth of diamond formation varies from the lower lithosphere in the upper part of the upper mantle (≈150-250 km) to the bottom of the lower mantle. At the same time, the diamonds containing mineral inclusions, characteristic of the lower mantle, account for only the first percents of the general number of diamonds. Conclusions. The transport of diamonds from different depths of their origin is a reliable indication of convection processes (as a plume activity) in the mantle. This information provides evidence to the real existence of plumes, which is important in the context of ongoing discussions on the depth of their origin. However, the study of mineral inclusions in diamonds, particularly in superdeep diamonds, is a challenging task due to the retrograde changes, resorption and sometimes complete dissolution on their way to the surface. These circumstances minimize the probability of occurrence of superdeep diamonds and require consideration when making judgements about the reality of existence of superdeep diamonds.

The role of subduction in the formation of Pangaean oceanic large igneous provinces

Abstract Large igneous provinces (LIPs) have been linked to both surface and deep mantle processes. During the formation, tenure and break-up of the supercontinent Pangaea, there is an increase in emplacement events for both continental and oceanic LIPs. There is currently no clear consensus on the origin of LIPs, but a hypothesis relates their formation to crustal emplacement of hot plume material originating in the deep mantle. The interaction of subducted slabs with the lowermost mantle thermal boundary and subsequent return flow is a key control on such plume generation. This mechanism has been explored for LIPs below the interior of a supercontinent (i.e. continental LIPs). However, a number of LIPs formed exterior to Pangaea (e.g. Ontong Java Plateau), with no consensus on their formation mechanism. Here, we consider the dynamics of supercontinent processes as predicted by numerical models of mantle convection and analyse whether circum-supercontinent subduction could generate both interior (continental) and exterior (oceanic) deep mantle plumes. Our numerical models show that subduction related to the supercontinent cycle can reproduce the location and timing of the Ontong Java Plateau, Caribbean LIP and potentially the Shatsky Rise by linking the origin of these LIPs to the return flow that generated deep mantle exterior plumes.

The Volcanic and Radial Expansion/Contraction History of the Moon Simulated by Numerical Models of Magmatism in the Convective Mantle

AbstractTo understand the evolution of the Moon, we numerically modeled mantle convection and magmatism in a two‐dimensional polar rectangular mantle. Magmatism occurs as an upward permeable flow of magma generated by decompression melting through the convecting matrix. The mantle is assumed to be initially enriched in heat‐producing elements (HPEs) and compositionally dense ilmenite‐bearing cumulates (IBC) at its base. Here, we newly show that magma generation and migration play a crucial role in the calculated volcanic and radial expansion/contraction history. Magma is generated in the deep mantle by internal heating for the first several hundred million years. A large volume of the generated magma ascends to the surface as partially molten plumes driven by melt buoyancy; the magma generation and ascent cause a volcanic activity and radial expansion of the Moon with the peak at 3.5–4 Gyr ago. Eventually, the Moon begins to radially contract when the mantle solidifies by cooling from the surface boundary. As the mantle is cooled, the activity of partially molten plumes declines but continues for billions of years after the peak because some basal materials enriched in the dense IBC components hold HPEs. The calculated volcanic and radial expansion/contraction history is consistent with the observed history of the Moon. Our simulations suggest that a substantial fraction of the mantle was solid, and there was a basal layer enriched in HPEs and the IBC components at the beginning of the history of the Moon.

Seismic Imaging Beneath Cascadia Shows Shallow Mantle Flow Patterns Guide Lower Mantle Upwellings

AbstractThe mantle transition zone (MTZ) plays an important role in modulating material transport between the upper mantle and the lower mantle. Constraining this transport is essential for understanding geochemical reservoirs, hydration cycles, and the evolution of the Earth. Slabs and hotspots are assumed to be the dominant locations of transport. However, the degree of material transport in other areas is debated. We apply P‐to‐S receiver functions to an amphibious data set from Cascadia to image the MTZ discontinuities beneath mid‐ocean ridges, a hotspot, and a subduction zone. We find a MTZ thinned by 10 ± 6 km beneath the ridges and by 8 ± 4 km beneath the base of the slab, closely resembling the 660 discontinuity topography. Depressions on the 410 discontinuity are smaller, 5 ± 2 km on average, focused in the north and the south and accompanied by supra‐410 discontinuity melt phases. The depressions occur away from locations of uplifted 660 discontinuity, but near slow seismic velocity anomalies imaged in the upper mantle. This suggests lower mantle upwellings occur beneath ridges and beneath the base of slabs but stall in the transition zone, with upper mantle convection determining upward material transport from the transition zone. Therefore, upper mantle dynamics play a larger role in determining transfer than typically assumed.

GLOBAL GEODYNAMIC MODEL OF THE EARTH AND ITS APPLICATION FOR ANTARCTICA

A geodynamic model of the modern Earth is constructed based on the SMEAN 2 global seismic tomography model. On the basis of mantle temperature anomalies, numerical modeling of spherical mantle convection is performed for the parameters of the real Earth. For Antarctica, an explanation was obtained for the existence of the West Antarctic Rift System, which contains one of the largest and least known volcanic provinces on Earth, which is consistent with the increased surface heat flow and modern volcanism of the West Antarctic Rift System and part of the Antarctic Peninsula. The increased heat flow and volcanoes in this region are causing instability and accelerating the flow of glaciers from the West Antarctic Ice Sheet into the ocean, which could lead to a significant rise in global sea level.

Numerical modeling of stresses and deformation in the Zagros–Iranian Plateau region

Abstract. The Zagros orogenic system resulted due to collision of the Arabian plate with the Eurasian plate. The region is characterized by ocean–continent subduction and continent–continent collision, and the convergence velocity shows variations from east to west. Therefore, this region shows the complex tectonic stress and a wide range of diffuse or localized deformation between both plates. The in situ stress and GPS data are very limited and sparsely distributed in this region; therefore, we performed a numerical simulation of the stresses causing deformation in the Zagros–Iran region. The deviatoric stresses resulting from the variations in lithospheric density and thickness and those from shear tractions at the base of the lithosphere due to mantle convection were computed using thin-sheet approximation. Stresses associated with both sources can explain various surface observations of strain rates, SHmax, and plate velocities, thus suggesting a good coupling between lithosphere and mantle in most parts of Zagros and Iran. As the magnitude of stresses due to shear tractions from density-driven mantle convection is higher than those from lithospheric density and topography variations in the Zagros–Iranian Plateau region, mantle convection appears to be the dominant driver of deformation in this area. However, the deformation in the east of Iran is caused primarily by lithospheric stresses. The plate velocity of the Arabian plate is found to vary along the Zagros belt from the north–northeast in the southeast of Zagros to the northwest in northwestern Zagros, similarly to observed GPS velocity vectors. The output of this study can be used in seismic hazards estimations.

Pangaea's breakup: the roles of mantle plumes, orogens and subduction retreat

Abstract What drives the breakup of a supercontinent remains contentious. Previously proposed mechanisms include mantle plumes, subduction retreat and basal traction from mantle convection. Here we review the geological record of plumes, orogens and subduction zones during the breakup of Pangaea and investigate the potential roles played by these factors through 4D spherical geodynamic modelling. We found that mantle plumes provided the dominant force that drove the breakup of Pangaea, particularly in triggering the initial breakup. Young orogens as continental lithospheric weak zones generally guided the development of continental rifts, consistent with the geological record that rifting within Pangaea commonly developed along pre-existing orogens. However, the marginal drag force produced by subduction retreat, and basal traction associated with subduction-related mantle flow, likely also played a role in the breakup of Pangaea. In addition, the weakening effect of plume-induced melts can sometimes help to break the continental lithosphere away from orogens, as exemplified by the breakup between Antarctica and Australia. Furthermore, geodynamic modelling suggests that subduction is responsible for generating mantle plumes. A particular such example is the formation of the Kerguelen plume, triggered by subduction along the northern margin of Australia, which facilitated the breakup between East Antarctica and Australia.

FoilTrack: a package to increase strain-resolution by improved X-radiographic image processing

ABSTRACT In high pressure multi-anvil experiments X-radiography is used to ascertain strain in deforming samples because the tooling prevents optical or other direct observations of the sample. The processing of these X-radiographic images to determine bulk sample strain is one of the limiting factors to making measurements closer to the strains and strain-rates that occur during mantle convection or the passage of seismic waves. Typically, sample deformation in these experiments is tracked by the displacement of high-contrast marker foils in X-radiographs. X-radiographs are treated individually or pairwise in a multi-step process that tracks the displacement of marker foils during experiments. Here I develop a new algorithm, FoilTrack, that treats all the X-radiographic observations in a single-step process, resulting in improved accuracy and consistency of length changes determined from X-radiographic images, as well as providing more realistic parameter uncertainty. The improvements are demonstrated using data from small-strain sinusoidal deformation experiments.

Rapid transition from primary to secondary crust building on the Moon explained by mantle overturn

Geochronology indicates a rapid transition (tens of Myrs) from primary to secondary crust building on the Moon. The processes responsible for initiating secondary magmatism, however, remain in debate. Here we test the hypothesis that the earliest secondary crust (Mg-suite) formed as a direct consequence of density-driven mantle overturn, and advance 3D mantle convection models to quantify the resulting extent of lower mantle melting. Our modeling demonstrates that overturn of thin ilmenite-bearing cumulates ≤ 100 km triggers a rapid and short-lived episode of lower mantle melting which explains the key volume, geochronological, and spatial characteristics of early secondary crust building without contributions from other energy sources, namely KREEP (potassium, rare earth elements, phosphorus, radiogenic U, Th). Observations of globally distributed Mg-suite eliminate degree-1 overturn scenarios. We propose that gravitational instabilities in magma ocean cumulate piles are major driving forces for the onset of mantle convection and secondary crust building on differentiated bodies.

Influence of the asthenosphere on earth dynamics and evolution

The existence of a thin, weak asthenospheric layer beneath Earth’s lithospheric plates is consistent with existing geological and geophysical constraints, including Pleistocene glacio-isostatic adjustment, modeling of gravity anomalies, studies of seismic anisotropy, and post-seismic rebound. Mantle convection models suggest that a pronounced weak zone beneath the upper thermal boundary layer (lithosphere) may be essential to the plate tectonic style of convection found on Earth. The asthenosphere is likely related to partial melting and the presence of water in the sub-lithospheric mantle, further implying that the long-term evolution of the Earth may be controlled by thermal regulation and volatile recycling that maintain a geotherm that approaches the wet mantle solidus at asthenospheric depths.

Small-scale heterogeneities in the convective upper mantle beneath circum-Pacific subduction zones: Evidence for fragments of recycled basaltic crust

We show evidence for the presence of compositional heterogeneities at 10 km scale in the convective upper mantle below the circum-Pacific subduction zones. By array-processing we examine seismograms of intermediate-depth earthquakes recorded by large-aperture seismic networks at teleseismic distances. In the P coda until about 25 s after direct P waves, we observe anomalous and significant signals arriving from the directions close to the P waves. The amplitude and duration of the signals decrease with focal depth within the range from about 180 to 300 km. We show that the signals arise mainly from S-to-P scattering in the mantle below the foci. Using the scattering theory for randomly heterogeneous media we also show that the observed features of the signals are matched by 5 to 10 km-scale density and rigidity anomalies that diminish below about 400 km depth. The rigidity anomaly is of the same sign and nearly twice as large as the density anomaly. These properties of the scattering objects could be consistent with basalt embedded in depleted mantle. The results indicate that the upper mantle transition zone beneath subducting slabs is not well mixed even by vigorous convection.

Effects of Composite Rheology on Plate‐Like Behavior in Global‐Scale Mantle Convection

AbstractEarth's upper mantle rheology controls lithosphere‐asthenosphere coupling and thus surface tectonics. Rock deformation experiments and seismic anisotropy measurements indicate that composite rheology (co‐existing diffusion and dislocation creep) occurs in the Earth's uppermost mantle, potentially affecting convection and surface tectonics. Here, we investigate how the spatio‐temporal distribution of dislocation creep in an otherwise diffusion‐creep‐controlled mantle impacts the planform of convection and the planetary tectonic regime as a function of the lithospheric yield strength in numerical models of mantle convection self‐generating plate‐like tectonics. The low upper‐mantle viscosities caused by zones of substantial dislocation creep produce contrasting effects on surface dynamics. For strong lithosphere (yield strength > 35 MPa), the large lithosphere‐asthenosphere viscosity contrasts promote stagnant‐lid convection. In contrast, the increase of upper mantle convective vigor enhances plate mobility for lithospheric strength <35 MPa. For the here‐used model assumptions, composite rheology does not facilitate the onset of plate‐like behavior at large lithospheric strength.

Equation of state for Mg3Al2Si3O12 pyrope: Implications for post-garnet transitions and mantle dynamics

Mantle convection is the dominant process driving the upwelling of hot materials and subduction of cold slabs. These processes are density-dependent and influenced by post-spinel and post-garnet transitions in the mantle transition zone (MTZ)/ lower mantle (LM). Knowledge of the Clapeyron slope of these transformations is used to express the dynamics of mantle blocks and is necessary for understanding the deep Earth. Here, we provide the Kunc-Einstein equation of state (EoS) for the pyrope Mg3Al2Si3O12 (Prp) calculated from a joint analysis of the experimentally measured isobaric heat capacity, bulk moduli, thermal expansion, pressure (P), unit cell volume (V), temperature (T) data. Based on our model, the bulk modulus and its pressure derivatives were K0,T0 = 168.5 GPa, K′0,T = 4.77, and V0 = 1501.7 Å. The optimised parameters include two Einstein temperatures, i.e., θ1 = 331 and θ2 = 1093 K, Grüneisen parameter at ambient condition γ0 = 1.77, infinite compression γ∞ = 0 with β = 1.12 and an intrinsic anharmonicity parameter a0 = –20. The value for the thermal expansion coefficient was calculated to be α = 2.33·10−5 K−1, and the thermodynamic Grüneisen parameter was estimated as γth = 1.42. The obtained EoS for Prp and the preliminarily fitted EoS for Al-bearing akimotoite (Al-Aki), in combination with literature data on bridgmanite (Bdm) and corundum (Crn), allowed the calculation of the phase diagram of the system with 75 mol% MgSiO3 + 25 mol% Al2O3 under LM conditions. The transformation from Prp to Bdm + Crn was computed at 24 GPa and 1570 K and exhibited a slightly positive Clapeyron slope (dP/dT = 2.1 MPa/K). The stability field of Al-Aki was detected at T = 1250–1570 K and P = 23–27 GPa. At P values higher than 24–27 GPa, the Al-Aki transforms into a Bdm + Crn assemblage with a highly negative Clapeyron slope. Calculations of sound velocities for the studied phases showed that the transformation from Prp to Bdm + Crn increased Vp and Vs by up to 9 and 20%, respectively. Such a big jump in the sound velocities indicates that the post-garnet transition is a better candidate than the post-Aki transition for producing a double discontinuity at the base of the MTZ, in combination with the transformation of ringwoodite into the Bdm + ferropericlase assemblage. The increase in sound velocities associated with the formation and dissolution of Al-Aki is unlikely to be sensitive to the MTZ. The combination of post-garnet, post-spinel, and post-Aki transitions near 660–720 km depths may have sluggished both the upwelling hot mantle and the subducted cold plates. The stagnant, hot LM material at the base of MTZ warmed the harzburgite and eclogite layers stacked during subduction. The heated MTZ may have been involved in further upwelling.

High‐Resolution Mantle Flow Models Reveal Importance of Plate Boundary Geometry and Slab Pull Forces on Generating Tectonic Plate Motions

AbstractMantle convection models based on geophysical constraints have provided us with a basic understanding of the forces driving and resisting plate motions on Earth. However, existing studies computing the balance of underlying forces are contradicting, and the impact of plate boundary geometry on surface deformation remains unknown. We address these issues by developing global instantaneous 3‐D mantle convection models with a heterogeneous density and viscosity distribution and weak plate boundaries prescribed using different geometries. We find that the plate boundary geometry of the Global Earthquake Model (GEM, Pagani et al., 2018, https://doi.org/10.1177/8755293020931866), featuring open plate boundaries with discrete lithospheric‐depth weak zones in the oceans and distributed crustal faults within continents, achieves the best fit to the observed GPS data with a directional correlation of 95.1% and a global point‐wise velocity residual of 1.87 cm/year. A good fit also requires plate boundaries being 3 to 4 orders of magnitude weaker than the surrounding lithosphere and low asthenospheric viscosities between 5 × 1017 and 5 × 1018 Pa s. Models without asthenospheric and lower mantle heterogeneities retain on average 30% and 70% of the plate speeds, respectively. Our results show that Earth's plate boundaries are not uniform and better described by more discrete plate boundaries within the oceans and distributed faults within continents. Furthermore, they emphasize the impact of plate boundary geometry on the direction and speed of plate motions and reaffirm the importance of slab pull in the uppermost mantle as a major plate driving force.

Inferring the relationship between core-mantle heat flux and seismic tomography from mantle convection simulations

The heat flux pattern at Earth’s core-mantle boundary (CMB) imposes a heterogeneous boundary condition on core dynamics that may profoundly affect the geodynamo. Owing to the expected temperature dependence of seismic velocities, this pattern is classically approximated as proportional to the lowermost layer of seismic tomography models for the global mantle. Two biases however undermine such a simple linear relationship: 1) other contributions than thermal (compositional and mineralogical) influence seismic velocities and 2) the radial average is inherent to tomographic models whereas the local thermal state at the CMB is relevant for the heat flux. We analyze here simulations of thermochemical mantle convection where, owing to their spatial characteristics, specific mantle components are readily identified: hot thermochemical piles (TCPs), “normal” mantle (NM) and, when post-peroskite (pPv) is included, a cold region where this phase is present. Synthetic seismic velocities (i.e. from the mantle simulations) are then computed based on thermal, compositional and mineralogical sensitivities. A formalism to infer the CMB heat flux from these seismic shear velocity anomalies is derived. In this formalism, within each mantle population (i.e. TCPs, NM or pPv) the CMB heat flux vs. seismic anomalies follows a unique fitting function. The transition from one mantle population to another is marked by a jump in the seismic anomaly, i.e. a range of seismic anomalies in between two mantle populations corresponds to a similar CMB heat flux. Applying our formalism to the seismic anomalies from the mantle convection simulations provides far superior fits than the commonly used linear fits. The results highlight reduced negative heat flux anomalies beneath large low shear velocity provinces (LLSVPs), while positive heat flux anomalies are enhanced, both with respect to the classical linear interpretation.

Effect of the supercontinent cycle on the longest-term sea-level change from a simple conceptual and theoretical model

The longest-term (first-order) sea-level change is considered to be within ∼ 200–300 million years, which is roughly half or less of the period of the supercontinent cycle of ∼ 500–700 Myr. It is recognized that the assembly of supercontinents involves either the closure of the “interior ocean” that resulted from the breakup of the supercontinent or the closure of the “exterior ocean” that surrounded the supercontinent. The former process is termed “extroversion,” while the latter is termed “introversion,” both of which are an end-member scenario of the supercontinent cycle. A “combination” process is also proposed to explain the complex behavior of continental drift on the actual Earth. Despite recent advances in a time-dependent mantle convection model, some difficulties still remain in self-consistently recovering plate tectonics and continental drift of the past Earth. Therefore, it is worth addressing the fundamental physics of the effects of the history of plate motion and the associated continental drift on the longest-term sea-level change from the perspevtive of the supercontinent cycle in a timescale of the order of 100 million years. In this study, a simple conceptual model of mantle convection with various supercontinent cycle processes was constructed, and the effects of the supercontinent cycle on the longest-term sea-level change were addressed. The sea-level change is estimated from bathymetry over the oceanic plates under different free parameters that control the fluctuation of the sea-level change. The present analytical results suggest that the asymptotic bathymetry due to the plate flattening effect of oceanic plates in the exterior and interior oceans is essential to recover the realistic magnitude of sea-level fluctuations that is comparable to the sea-level curve of the past Earth. In addition, the absolute volume change in the seawater due to its recycling into the mantle may be important to fit the observed sea-level curves from stratigraphic studies since 200 million years ago.