Impact of upper mantle convection on lithosphere hyperextension and subsequent horizontally forced subduction initiation

Abstract. Many plate tectonic processes, such as subduction initiation, are embedded in long-term (>100 Myr) geodynamic cycles often involving subsequent phases of extension, cooling without plate deformation and convergence. However, the impact of upper mantle convection on lithosphere dynamics during such long-term cycles is still poorly understood. We have designed two-dimensional upper-mantle-scale (down to a depth of 660 km) thermo-mechanical numerical models of coupled lithosphere–mantle deformation. We consider visco–elasto–plastic deformation including a combination of diffusion, dislocation and Peierls creep law mechanisms. Mantle densities are calculated from petrological phase diagrams (Perple_X) for a Hawaiian pyrolite. Our models exhibit realistic Rayleigh numbers between 106 and 107, and the model temperature, density and viscosity structures agree with geological and geophysical data and observations. We tested the impact of the viscosity structure in the asthenosphere on upper mantle convection and lithosphere dynamics. We also compare models in which mantle convection is explicitly modelled with models in which convection is parameterized by Nusselt number scaling of the mantle thermal conductivity. Further, we quantified the plate driving forces necessary for subduction initiation in 2D thermo-mechanical models of coupled lithosphere–mantle deformation. Our model generates a 120 Myr long geodynamic cycle of subsequent extension (30 Myr), cooling (70 Myr) and convergence (20 Myr) coupled to upper mantle convection in a single and continuous simulation. Fundamental features such as the formation of hyperextended margins, upper mantle convective flow and subduction initiation are captured by the simulations presented here. Compared to a strong asthenosphere, a weak asthenosphere leads to the following differences: smaller value of plate driving forces necessary for subduction initiation (15 TN m−1 instead of 22 TN m−1) and locally larger suction forces. The latter assists in establishing single-slab subduction rather than double-slab subduction. Subduction initiation is horizontally forced, occurs at the transition from the exhumed mantle to the hyperextended passive margin and is caused by thermal softening. Spontaneous subduction initiation due to negative buoyancy of the 400 km wide, cooled, exhumed mantle is not observed after 100 Myr in model history. Our models indicate that long-term lithosphere dynamics can be strongly impacted by sub-lithosphere dynamics. The first-order processes in the simulated geodynamic cycle are applicable to orogenies that resulted from the opening and closure of embryonic oceans bounded by magma-poor hyperextended rifted margins, which might have been the case for the Alpine orogeny.

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Impact of upper mantle convection on lithosphere hyper-extension and subsequent convergence-induced subduction

10.5194/se-2020-88 ◽

2020 ◽

Author(s):

Lorenzo G. Candioti ◽

Stefan M. Schmalholz ◽

Thibault Duretz

Keyword(s):

Upper Mantle ◽

Mantle Convection ◽

Numerical Models ◽

Unit Length ◽

Mantle Flow ◽

Suction Force ◽

Continuous Simulation ◽

Passive Margins ◽

Low Viscosity ◽

Lower Viscosity

Abstract. We present two-dimensional thermo-mechanical numerical models of coupled lithosphere-mantle deformation, considering the upper mantle down to a depth of 660 km. We consider visco-elasto-plastic deformation and for the lithospheric and upper mantle a combination of diffusion, dislocation and Peierls creep. Mantle densities are calculated from petrological phase diagrams (Perple_X) for a Hawaiian pyrolite. The model generates a 120 Myrs long geodynamic cycle of subsequent extension (30 Myrs), cooling (70 Myrs) and convergence (20 Myrs) in a single and continuous simulation with explicitly modelling convection in the upper mantle. During lithosphere extension, the models generate an approximately 400 km wide basin of exhumed mantle bounded by hyper-extended passive margins. The models show that considering only the thermal effects of upper mantle convection by using an effective thermal conductivity generates results of lithosphere hyper-extension that are similar to the ones of models that explicitly model the convective flow. Applying a lower viscosity limit of 5 × 1020 Pa s suppresses convection and generates results different to the ones for simulations with a low viscosity asthenosphere having minimal viscosity of approximately 1019 Pa s. During cooling without far-field deformation, no subduction of the exhumed mantle is spontaneously initiated. Density differences between lithosphere and mantle are too small to generate a buoyancy force exceeding the mechanical strength of the lithosphere. The extension and cooling stages generate self-consistently a structural and thermal inheritance for the subsequent convergence stage. Convergence initiates subduction of the exhumed mantle at the transition to the hyper-extended margins. The main mechanism of subduction initiation is thermal softening for a plate driving force (per unit length) of approximately 15 TN m−1. If convection in the mantle is suppressed by high effective thermal conductivities or high, lower viscosity limits, then subduction initiates at both margins leading to divergent double-slab subduction. Convection in the mantle assists to generate a single-slab subduction at only one margin, likely due to mantle flow which exerts an additional suction force on the lithosphere. The first-order geodynamic processes simulated in the geodynamic cycle of subsequent extension, cooling and convergence are applicable to orogenies that resulted from the opening and closure of embryonic oceans bounded by magma-poor hyper-extended passive margins, which might have been the case for the Alpine orogeny. 

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The importance of phase morphology for rheology of ferropericlase-bridgmanite mixtures

10.5194/egusphere-egu21-4384 ◽

2021 ◽

Author(s):

Marcel Thielmann ◽

Gregor Golabek ◽

Hauke Marquardt

Keyword(s):

Lower Mantle ◽

Mantle Convection ◽

Effective Viscosity ◽

Large Scale ◽

Numerical Models ◽

Phase Morphology ◽

Strong Impact ◽

Analytical Approximations ◽

The Impact ◽

Strong Control

The rheology of the Earth&#8217;s lower mantle is poorly constrained due to a lack of knowledge of the rheological behaviour of its constituent minerals. In addition, the lower mantle does not consist of only a single, but of multiple mineral phases with differing deformation behaviour. The rheology of Earth&#8217;s lower mantle is thus not only controlled by the rheology of its individual constituents (bridgmanite and ferropericlase), but also by their interplay during deformation. This is particularly important when the viscosity contrast between the different minerals is large. Experimental studies have shown that ferropericlase may be significantly weaker than bridgmanite and may thus exert a strong control on lower mantle rheology.Here, we thus explore the impact of phase morphology on the rheology of a ferropericlase-bridgmanite mixture using numerical models. We find that elongated ferropericlase structures within the bridgmanite matrix significantly lower the effective viscosity, even in cases where no interconnected network of weak ferropericlase layers has been formed. In addition to the weakening, elongated ferropericlase layers result in a strong viscous anisotropy. Both of these effects may have a strong impact on lower mantle dynamics, which makes is necessary to develop upscaling methods to include them in large-scale mantle convection models. We develop a numerical-statistial approach to link the statistical properties of a ferropericlase-bridgmanite mixture to its effective viscosity tensor. With this approach, both effects are captured by analytical approximations that have been derived to describe the evolution of the effective viscosity (and its anisotropy) of a two-phase medium with aligned elliptical inclusions, thus allowing to include these microscale processes in large-scale mantle convection models.

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Breaking supercontinents; no need to choose between passive or active

Solid Earth ◽

10.5194/se-8-817-2017 ◽

2017 ◽

Vol 8 (4) ◽

pp. 817-825 ◽

Cited By ~ 4

Author(s):

Martin Wolstencroft ◽

J. Huw Davies

Keyword(s):

Upper Mantle ◽

Numerical Models ◽

Finite Geometry ◽

Fundamental Principle ◽

Global Perspective ◽

Return Flow ◽

Future Studies ◽

Extensional Stress ◽

Break Up ◽

The Impact

Abstract. Much debate has centred on whether continental break-up is predominantly caused by active upwelling in the mantle (e.g. plumes) or by long-range extensional stresses in the lithosphere. We propose the hypothesis that global supercontinent break-up events should always involve both. The fundamental principle involved is the conservation of mass within the spherical shell of the mantle, which requires a return flow for any major upwelling beneath a supercontinent. This shallow horizontal return flow away from the locus of upwelling produces extensional stress. We demonstrate this principle with numerical models, which simultaneously exhibit both upwellings and significant lateral flow in the upper mantle. For non-global break-up the impact of the finite geometry of the mantle will be less pronounced, weakening this process. This observation should motivate future studies of continental break-up to explicitly consider the global perspective, even when observations or models are of regional extent.

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Impact-induced crustal dichotomy on Mars: from SPH to long-term mantle convection models

10.5194/egusphere-egu2020-10248 ◽

2020 ◽

Author(s):

Kar Wai Cheng ◽

Antoine B. Rozel ◽

Harry Ballantyne ◽

Martin Jutzi ◽

Gregor J. Golabek ◽

...

Keyword(s):

Mantle Convection ◽

Thickness Distribution ◽

Three Dimensional ◽

Physical Nature ◽

Hybrid Origin ◽

Geophysical Research ◽

Probable Impact ◽

The Impact ◽

Crustal Dichotomy

The formation process of the crustal dichotomy of Mars has remained elusive since its discovery more than three decades ago.&#160; Workers put forward different theories including (i) an endogenic origin, where the dichotomy is formed by degree-1 mantle convection [1, 2]; (ii) an exothermic origin, where the northern crust is excavated by an impact [3]; and (iii) a hybrid origin, where an impact generated large amounts of melt, followed by crust production shaping the crustal dichotomy [4].&#160;In this study we focus on the last hypothesis. Our previous results using a parameterized impact show that a dichotomy can be formed in this manner.&#160; In order to confirm whether these results still hold when using a realistic impact, and to consider the most probable impact angles and velocities, a SPH code [5] is used to model both the impact itself and the first 24 hours of post-impact evolution. The result is then transferred into mantle convection code StagYY [6] in order to simulate the long-term evolution of both crust and mantle for 4.5 Gyrs.&#160; Due to the different physical nature and assumptions between the SPH impact models and long-term mantle convection models, care in data treatment is required when coupling the two simulations.&#160; In this study, different setups regarding the transfer of data are tested and explored, including the treatment of temperature profiles, the choice of density and viscosity of materials, and the time of transfer.Preliminary results from coupled SPH-geodynamics evolution models are presented, involving the crust thickness and topography maps after 4.5 Gyrs of evolution.&#160;[1] Roberts, J., & Zhong, S. (2006). Degree-1 convection in the Martian mantle and the origin of the hemispheric dichotomy. Journal Of Geophysical Research, 111(E6).[2] Keller, T., & Tackley, P. (2009). Towards self-consistent modeling of the martian dichotomy: The influence of one- ridge convection on crustal thickness distribution. Icarus, 202(2), 429-443.[3] Andrews-Hanna, J., Zuber, M., & Banerdt, W. (2008). The Borealis basin and the origin of the martian crustal dichotomy. Nature, 453(7199), 1212-1215.[4] Golabek, G., Keller, T., Gerya, T., Zhu, G., Tackley, P., & Connolly, J. (2011). Origin of the martian dichotomy and Tharsis from a giant impact causing massive magmatism. Icarus, 215(1), 346-357.[5] Emsenhuber, A., Jutzi, M., Benz, W. (2018). SPH calculations of Mars-scale collisions: The role of the equation of state, material rheologies, and numerical effects. Icarus, 301, 247-257[6] Tackley, P. (2008). Modelling compressible mantle convection with large viscosity contrasts in a three- dimensional spherical shell using the yin-yang grid. Physics Of The Earth And Planetary Interiors, 171(1-4), 7-18.

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Whole-mantle convection with tectonic plates preserves long-term global patterns of upper mantle geochemistry

Scientific Reports ◽

10.1038/s41598-017-01816-y ◽

2017 ◽

Vol 7 (1) ◽

Cited By ~ 8

Author(s):

T. L. Barry ◽

J. H. Davies ◽

M. Wolstencroft ◽

I. L. Millar ◽

Z. Zhao ◽

...

Keyword(s):

Upper Mantle ◽

Mantle Convection ◽

Tectonic Plates ◽

Mantle Geochemistry ◽

Global Patterns

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Driving Forces of Forest Landscape Change in Ślęża Landscape Park (Southwestern Poland) in Period 1883-2013

10.20944/preprints201808.0533.v1 ◽

2018 ◽

Cited By ~ 1

Author(s):

Piotr Krajewski ◽

Iga Solecka ◽

Karol Mrozik

Keyword(s):

Driving Forces ◽

Demographic Data ◽

Buffer Zone ◽

Global Perspective ◽

Forest Landscape ◽

Location Factors ◽

Landscape Transformations ◽

The Impact ◽

Socio Economic Factors

Abstract: Changes in forest landscapes have been connected with human activity for centuries, which can be considered as one of the main driving forces of change in the global perspective. The spatial distribution of forests changes along with the geopolitical situation, demographic changes, intensification of agriculture, urbanization or changes in the land use policy. However, due to the limited availability of historical data, the driving forces of changes in forest landscapes are most often considered in relation to recent decades, without taking into account long-term analyzes. The aim of this paper is to determine the impact of natural and socio-economic factors on changes in forest landscapes within the protected area – Ślęża Landscape Park and its buffer zone in the aspect of long-term analyzes covering the period of 140 years (1883-2013). The comparison of historical and current maps, demographic data on 4 different periods as well as natural and location factors by using the ArcGIS software allowed analyzing selected driving forces of forest landscape transformations. We took into account natural factors like altitude, slope, exposure of the hillside and socio-economic drivers like population changes, distances to centers of municipalities, main roads and built-up areas.

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Forced subduction initiation at passive continental margins: Numerical modeling

10.5194/egusphere-egu2020-1761 ◽

2020 ◽

Author(s):

Xinyi Zhong ◽

Zhong-Hai Li

Keyword(s):

Subduction Zones ◽

Plate Tectonics ◽

Numerical Models ◽

Oceanic Lithosphere ◽

Ocean Basin ◽

Passive Margin ◽

Complex Case ◽

Subduction Initiation ◽

Boundary Force ◽

Time Required

Subduction initiation (SI) induced by the tectonic boundary force may play a significant role in the Wilson cycle. In the previous analog and numerical models, the constant convergent velocity is generally applied, which may lead to large boundary forces for SI. In this study, we begin with testing the simple case of SI at passive margin with constant convergent force. The results indicate that the boundary force required to trigger the SI at passive margin with a thin and young oceanic lithosphere is much lower than that with a thick and old one. It is consistent with the multiple Cenozoic subduction zones in the Southwest Pacific, which are young ocean basin within 40 Ma and compressed by the India-Australia plate. Furthermore, we extended our model to explore a more complex case, forced SI during the collision-induced subduction transference, which is critical for Tethyan evolution. Both collision and SI processes are integrated in the numerical models. The results indicate that the forced convergence, rather than pure free subduction, is required to trigger and sustain the SI in the neighboring passive margin after collision of terrane. In addition, a weak passive margin can significantly promote the occurrence of subduction initiation, by decreasing required boundary force within reasonable range of plate tectonics. However, the lengths of subducted oceanic slab and accreting terrane play secondary roles in the occurrence of SI after collision. Under the favorable conditions of collision-induced subduction transference, the time required for subduction initiation after collision is generally within 10 Myrs, which is consistent with the general geological records of Neo-Tethys. In contrast, both Atlantic passive margin and Indian passive margin are old and stable with absence of subduction initiation in the present, which remains an open question.

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Passive-margin delta stratigraphy from source-to-sink numerical models: parametric studies and comparison with natural systems

10.5194/egusphere-egu2020-18895 ◽

2020 ◽

Author(s):

Brendan Simon ◽

Cécile Robin ◽

Delphine Rouby ◽

Xiaoping Yuan ◽

Laure Guerit ◽

...

Keyword(s):

Landscape Evolution ◽

Numerical Models ◽

Input Parameter ◽

Passive Margin ◽

Geometrical Parameters ◽

Natural Systems ◽

Passive Margins ◽

Source To Sink ◽

Deposition Processes ◽

The Impact

One major and under-appreciated aspect of coupled erosion-deposition numerical modeling is the ranges of input parameter values used to simulate natural source to sink systems without considering their meaning in term of erosion, transport and deposition processes. Most of the time, numerical models are used as a semi-inversion tool based on a &#8220;best-fit&#8221; approach, especially in its marine part where it aims to reproduce well-constrained sedimentary architectures which are great recorders of landscape evolution through time.In this study, we performed several simulations using a new numerical landscape evolution model that accounts for both erosion and deposition onshore, as well as sediment deposition in the marine domain (Yuan et al., 2019; COLORS project, funded by Total). In the marine domain, sediment dynamic is described by a diffusion equation and the diffusion or transport coefficient has been calibrated from natural delta geometries. This model is highly efficient and allows the separation of the different processes involved and exploration of various setups and parameters values in order to address a large variety of questions. Its efficiency also allows inverse simulations that are powerful to determine the best possible scenarios in terms of climatic or tectonic reconstructions, or to determine the evolution of several key parameters.In order to evaluate the model reliability to reproduce realistic sedimentary geometries, we explore the impact of perturbations in climatic, eustatic or tectonic parameters of the model on the stratigraphic architecture of passive margins shelf-edge deltas and discuss its feedbacks with the erosion dynamic of the onshore domain. This sensitivity analysis also allowed us to define the most relevant geometrical parameters of observed or theoretical stratigraphic architectures that have to be include in the misfit function of the inversions and optimization scheme.This study is part of the COLORS project, funded by Total.

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The impact of rheological uncertainty on dynamic topography predictions: Gearing up for dynamic topography models consistent with observations

10.5194/se-2019-73 ◽

2019 ◽

Author(s):

Ömer F. Bodur ◽

Patrice F. Rey

Keyword(s):

Mantle Convection ◽

Numerical Models ◽

Mantle Flow ◽

Dynamic Topography ◽

Dynamic Component ◽

Density Anomaly ◽

Low Viscosity ◽

Local Reduction ◽

Non Linear ◽

The Impact

Abstract. Much effort has been given on extracting the dynamic component of the Earth’s topography, which is driven by density heterogeneities in the mantle. Seismically mapped density anomalies have been used as an input into mantle convection models to predict the present-day mantle flow and stresses applied on the Earth’s surface, resulting in dynamic topography. However, mantle convection models give dynamic topographies generally larger by a factor of ∼2 compared to dynamic topographies estimated from residual topography after extraction of the isostatically compensated topography. Our 3D thermo-mechanical numerical experiments suggest that this discrepancy can be explained by the use of a viscosity model, which doesn’t account for non-linear viscosity behaviour. In this paper, we numerically model the dynamic topography induced by a spherical density anomaly embedded into the mantle. When we use non-linear viscosities, our numerical models predict dynamic topographies lesser by a factor of ∼2 than those derived from numerical models using isoviscous rheology. This reduction in dynamic topography is explained by either the formation of a low viscosity channel beneath the lithosphere, or a decrease in thickness of the mechanical lithosphere due to induced local reduction in viscosity. Furthermore, we show that uncertainties related to activation volume and fluid activity, lead to variations in dynamic topography of about 20 %.

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Slab Remnant Recycling and Mantle-Wide Convection: A Separation of Time Scales

10.5194/egusphere-egu2020-2032 ◽

2020 ◽

Author(s):

Gary Jarvis

Keyword(s):

Time Scales ◽

Upper Mantle ◽

Lower Mantle ◽

Mantle Convection ◽

Numerical Models ◽

High Viscosity ◽

Mineral Phase ◽

Core Mantle Boundary ◽

The Core ◽

Very High

Two dimensional numerical models of mantle convection in a cylindrical shell provide a possible geodynamic explanation for cold patches in the mantle below India and Mongolia as detected by seismic tomography. We investigate the influence of very high viscosities at mid-mantle and lower-mantle depths, as proposed by Mitrovica and Forte (2004) and Steinberger and Calderwood (2006), on mantle convective flow.&#160; Models are considered with and without mineral phase transitions.&#160; Our viscosity profiles are depth dependent with deep mantle viscosities increasing to values of 300 times the viscosity of the upper mantle, and then decreasing dramatically on approaching the core-mantle boundary.&#160;&#160; The decrease of viscosity near the CMB mobilizes the overall mantle-wide flow despite very high mid-mantle viscosities.&#160; However, cold detached slabs sinking below continental collisions become captured by the high viscosity interior and circulate slowly for times exceeding 200 Myr.&#160; The separation of time scales for mantle-wide flow vs slab circulation, is a consequence of the high viscosity of the mid-mantle.

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