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Characteristics and geological significance of the stress state of the lithosphere in the Qinghai-Tibetan Plateau and its neighboring areas

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Science China Earth Sciences 2024年第6期67卷 1836-1855页

作者： Qianwen ZHANG Ya XU Wei CHU Shupeng LU Key Lab of Petroleum Resource Research Institute of Geology and GeophysicsChinese Academy of SciencesBeijing 100029China College of Earth and Planetary Sciences University of Chinese Academy of SciencesBeijing 100049China

The present-day lithospheric stress state of the Qinghai-Tibetan Plateau and neighboring areas is controlled by both the lithosphere itself and the underlying mantle.In other words,the stress is affected by the gravitational potential energy(GPE)difference caused by the change in the density distribution within the lithosphere and the drag force on the base of the lithosphere caused by Mantle convection.The study of the lithospheric stress state plays an important role in further understanding the dynamic background and mechanism for the evolution of the Qinghai-Tibetan Plateau.In this study,the Crust1.0 crustal density model combined with the S40RTS mantle shear wave velocity variation model was used to calculate the GPE.The EGM2008gravity field model was used to calculate the drag force from Mantle convection at the base of the lithosphere.The lithospheric and joint stress fields of the two sources were obtained by solving the force balance under the thin sheet approximation.This way,we could comprehensively analyze the characteristics of the stress state within the Plateau.Six regions were classified according to the GPE stress field,mantle drag force stress field,the relative magnitude of the two stress fields,and correlation between the two stress fields and surface deformation.The lithospheric stress fields of the Tarim Basin and other stable blocks are mainly controlled by the GPE difference.The lithospheric stress field in the collision zone between the Indian Plate and the QinghaiTibetan Plateau is predominantly controlled by the deep mantle drag force.The lithospheric stress field in the interior of the Plateau is controlled by both GPE and mantle drag.The correlation between the lithospheric stress field and surface deformation at the southeast margin of the Qinghai-Tibetan Plateau is poor.It is hypothesized that the presence of lower crustal flow with lower effective viscosity leads to crust-mantle decoupling,and the mantle drag force has a weaker influence on the shallow crust,resulting in the incons

关键词： Qinghai-Tibetan Plateau Gravitational potential energy Mantle convection Lithospheric deviatoric stress field GPS strain rate field

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Upper Mantle convection beneath northwest China and its adjacent region driven by density anomaly

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Acta Seismologica Sinica(English Edition) 2006年第5期19卷 552-562页

作者：许萍傅容珊黄建平查显杰戴志阳 CAS Key Laboratory of Crust-mantle Materials and Environments School of Earth and Space SciencesUni-versity of Science and Technology of China Earthquake Administration of Shandong Province Ji'nan 250014China

We assume that the density anomalies, which are transformed from seismic tomography data, are corresponding to temperature distribution in a convective mantle. We take density anomalies as the driving force for Mantle convection and solve the basic equation with given boundary conditions in a wave-number domain by using the FFT arithmetic. Using the physical model of upper Mantle convection and the seismic tomography data supplied by XU et al, we calculated upper Mantle convection beneath northwestern China and adjacent region. The flow patterns in the upper mantle show that there are upward and divergent flows in the basin regions, such as Tarim, Qaidam, Junggar and Kazakhstan, where the lithosphere is thin. There are downward and convergent flows in the mountain regions, such as Tianshan, Kunlun and Qilian, where the lithosphere is thick. In addition, because of the divergent flow under the Tarim Basin the upper mantle material in this region is driven southward to the north part of Tibetan Plateau and northward to Tianshan Mountain. Maybe, it is one of the reasons for the recent uplift of the Tianshaa Mountain.

关键词： Mantle convection northwestern China and its adjacent region seismic tomography

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Upper Mantle convection driving by density anomaly and a test model

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Acta Seismologica Sinica(English Edition) 2005年第1期18卷 27-33,124页

作者：傅容珊王景赟常筱华黄建华戴志阳查显杰 School of Earth and Space Science University of Science and Technology of China

A mathematic-physical convection model in upper mantle is established in this paper. This model is in a three dimensional frame. Assume that the density anomalies, which are mapped from the seismic tomography data, are responding to the temperature perturbation in the connective system. This model takes the density anomalies as the driving force for the Mantle convection. We solve the basic equations with different boundary conditions in a domination of wave number by using the FFT arithmetic. In order to test the validity of our theory and method two simple models (higher-lower density body and break off slab) are employed to calculate their flow patters in this paper. Results show that our method can be directly used to investigate the upper Mantle convection patterns and its related problems of lithospheric dynamics.

关键词： Mantle convection dynamics seismic tomography

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How Properties that Distinguish Solids from Fluids and Constraints of Spherical Geometry Suppress Lower Mantle convection

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Journal of Earth Science 2018年第1期29卷 1-20页

作者： Anne M. Hofmeister Everett M. Criss Department of Earth and Planetary Sciences Washington University St. Louis MO 63130 USA Panasonic Avionics Corporation Lake Forest CA 92630 USA

The large magnitude of the dimensionless Rayleigh number （Ra-10^8） for Earth＇s -3 000 km thick mantle is considered evidence of whole Mantle convection. However, the current formulation assumes behavior characteristic of gases and liquids and also assumes Cartesian geometry. Issues arising from neglecting physical properties unique to solids and ignoring the spherical shapes for planets include：（1） Planet radius must be incorporated into Ra, in addition to layer thickness, to conserve mass during radial displacements. （2） The vastly different rates for heat and mass diffusion in solids, which result from their decoupled transport mechanisms, promote stability. （3） Unlike liquids, sub- stantial stress is needed to deform solids, which independently promotes stability. （4） High interior compression stabilizes the mantle in additional minor ways. Therefore, representing conditions for convection in solid, self-gravitating spheroids, requires modifying formulae developed for bottom- heated fluids near ambient conditions under an invariant gravitational field. To derive stability criteria appropriate to solid spheres, we use dimensional analysis, and consider the effects of geometry, force competition, and microscopic behavior. We show that internal heating has been improperly ac- counted for in the Ra. We conclude that the lower mantle is stable for two independent reasons： heat diffusion far outpaces mass diffusion （creep） and yield strength of solids at high pressure exceeds the effective deviatoric stress. We discuss the role of partial melt in lubricating plate motion, and explain why the Ra is not applicable to the multi-component upper mantle. When conduction is insufficient to transport heat in the Earth, melt production and ascent are expected, not convection of solid rock.

关键词： plasticity diffusion Mantle convection stability criteria dimensional analysis geometry.

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Effects of depth-and composition-dependent thermal conductivity and the compositional viscosity ratio on the long-term evolution of large thermochemical piles of primordial material in the lower mantle of the Earth:Insights from 2-D numerical modeling

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Science China Earth Sciences 2023年第8期66卷 1865-1876页

作者： Yang LI Zhigang ZHANG Juan LI Zhidong SHI Liang ZHAO State Key Laboratory of Lithospheric Evolution Institute of Geology and GeophysicsChinese Academy of SciencesBeijing 100029China Key Laboratory of Earth and Planetary Physics Institute of Geology and GeophysicsChinese Academy of SciencesBeijing 100029China College of Earth and Planetary Science University of Chinese Academy of SciencesBeijing 100049China Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai) Zhuhai 519080China

Thermal conductivity plays an important role in the thermochemical evolution of Earth’s mantle.Recent mineral physics studies suggest that the thermal conductivity of the mantle varies with pressure and composition,and this may play an important role in the evolution of the Earth’s mantle.Meanwhile,the rheology of the deep mantle is also supposed to be composition-dependent.However,the dynamic influences of these factors remain not well understood.In this study,we performed numerical experiments of thermochemical Mantle convection in 2-D spherical annulus geometry to systematically investigate the effects of depth-and composition-dependent thermal conductivity and the compositional viscosity ratio on the long-term evolution of the large thermochemical structure of primordial material in Earth’s mantle.Our results show that increasing the depth-dependent thermal conductivity leads to a larger core-mantle boundary(CMB)heat flow and allows the formation of more stable large thermochemical piles(e.g.,Large Low Shear Velocity Provinces,LLSVPs);while decreasing the composition-dependent thermal conductivity would slightly destabilize the primordial thermochemical piles,increase the altitude of these piles and the temperature differences between the piles and the ambient mantle.If the primordial mantle material is compositionally more viscous(e.g.,20 times than that of the ambient mantle),the long-term stability of the thermochemical piles of primordial material decreases,and this destabilizing effect will be enhanced by decreasing the composition-dependent thermal conductivity.As a result,the thermochemical piles would be unstable in the core-mantle boundary region.Therefore,our study indicates that the combined effects of depth-and composition-dependent thermal conductivity and compositional viscosity ratio are pronounced to the thermochemical evolution of the mantle.

关键词： Mantle convection Thermal conductivity Core-mantle boundary heat flow Primordial mantle material LLSVPs

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True polar wander in the Earth system

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Science China Earth Sciences 2023年第6期66卷 1165-1184页

作者： Chong WANG Ross N.MITCHELL State Key Laboratory of Lithospheric Evolution Institute of Geology and GeophysicsChinese Academy of SciencesBeijing 100029China College of Earth and Planetary Sciences University of Chinese Academy of SciencesBeijing 100049China

True polar wander(TPW),or planetary reorientation,is the rotation of solid Earth(crust and mantle)about the liquid outer core in order to stabilize Earth’s rotation due to mass redistribution.Although TPW is well-documented on Earth presently with satellites and for multiple planets and moons in the Solar System,the prevalence of TPW in Earth history remains contentious.Despite a history of controversy,both the physical plausibility of TPW on Earth and an empirical basis for it are now undisputed.Lingering resistance to the old idea likely stems from the fact that,like plate tectonics,TPW may influence much of the Earth system,thus acknowledging its existence requires rethinking how many different datasets are interpreted.This review summarizes the development of TPW as a concept and provides a framework for future research that no longer regards TPW like a ghost process that may or may not exist,but as an integral part of the Earth system that can relate shallow and deep processes that are otherwise only mysteriously linked.Specifically,we focus on the temporal regularity of large TPW,and discuss its relationship with the supercontinent-megacontinent cycle based on previous studies.We suggest the assembly of megacontinents has a close linkage to large TPW.Meanwhile,supercontinent tenure and breakup have a close linkage to fast TPW.The effects of TPW on sea level changes,paleoclimate,biological diversity,and other facets of the Earth system are presented and require interdisciplinary tests in the future.

关键词： True polar wander(TPW) Planetary reorientation Apparent polar wander(APW) Mantle convection Supercontinent cycle Megacontinent

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Small-Scale Mineralogical Heterogeneity from Variations in Phase Assemblages in the Transition Zone and D" Layer Predicted by convection Modelling

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Journal of Earth Science 2011年第2期22卷 160-168页

作者： Arie P van den Berg David A Yuen Michael H G Jacobs Maarten V de Hoop Earth Sciences Department Utrecht University Department of Geology and Geophysics and Minnesota Supercomputing Institute University of MinnesotaMinneapolisMN 55415USA Institut für Metallurgie TU ClausthalClausthal-ZellerfeldGermany Department of Mathematics and Center of Applied and Computational Mathematics Purdue UniversityWest LafayetteINUSA

Small-scale heterogeneity in the deep mantle is concentrated in the upper-mantle transition zone （TZ）, in the depth range 410-660 km and also at the bottom 250 km D＂ region. This encourages a more detailed investigation of the potential for seismic reflectivity imaging by modelling heterogeneous structures in Mantle convection models including phase transitions of the TZ and D＂ regions. We applied finite elements with variable spacing near the boundary layers in 2-D cylindrical geometry that allow for sufficient spatial resolution. We investigated several models including an extended Boussinesq （EBA） model, focused on the D＂ region, and a compressible （ALA） model for the TZ region. The results for the D＂ region show typical lens-shaped structures of post-perovskite （PPV） embedded in the perovskite （PV） background mantle, where the thickness of the lenses, at 200-400 km, strongly depends on the Clapeyron slope of the PV-PPV transition. A second phase transition （double crossing） occurs in case the core temperature is higher than the intercept temperature Ti. Our phase-dependent rheology results in contrasting effective viscosity between PV and PPV. Our model results reveal a distinctly clear mechanical weakening of the PPV lenses with about an order of magnitude lower viscosity. The shear wave-speed distributions computed from our convection results are strongly correlated with the heterogeneous distribution of the mineral phase. Gradients in the seismic wave-speed that are the target of seismological reflectivity imaging are clearly revealed. The wave-speed results show a clear resolution of the top and bottom interfaces of the PPV lenses. Our ALA model for the TZ is based on a thermodynamical model for the magnesium end- member of an olivine-pyroxene mantle. The model predicts a much more complex distribution of mineral phases, compared to our D＂ results, in agreement with the greater number of mineral phases involved in the olivine-pyroxene phase diagram for the P, T conditions of the transition zone. Near cold

关键词： Mantle convection phase transition post-perovskite mineralogical heterogeneity.

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Linear Stability Analysis on the Influences of the Spatial Variations in Thermal Conductivity and Expansivity on the Flow Patterns of Thermal convection with Strongly Temperature-Dependent Viscosity

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Journal of Earth Science 2014年第1期25卷 126-139页

作者： Arata Miyauchi Masanori Kameyama Hiroki Ichikawa Geodynamics Research Center Ehime University

A series of linear stability analysis is carried out on the onset of thermal convection in the presence of spatial variations of viscosity, thermal conductivity and expansivity. We consider the temporal evolution of an infinitesimal perturbation superimposed to a static （motionless） and con- ductive state in a basally-heated planar layer. From the changes in flow patterns with increasing the amplitudes of temperature dependence of viscosity, we identified the transition into the ＂stagnant-lid＂（ST） regime, where the convection occurs only beneath a thick and stagnant-lid of cold fluid at the top surface. Detailed analysis showed a significant increase of the aspect ratio of convection cells in ST regime induced by the spatial variations in thermal conductivity and/or expansivity： the horizon- tal length scale of ST convection can be enlarged by up to 50% with 10 times increase of thermal conductivity with depth. We further developed an analytical model of ST convection which success- fully reproduced the mechanism of increasing horizontal length scale of ST regime convection cells for given spatial variations in physical properties. Our findings may highlight the essential roles of the spatial variation of thermal conductivity on the convection patterns in the mantle.

关键词： Mantle convection stagnant-lid temperature-dependent viscosity pressure- dependent thermal conductivity pressure-dependent thermal expansivity linear stability analysis.

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Dynamic features of the Tianshan orogen deduced from satellitic gravity data

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Acta Seismologica Sinica(English Edition) 2000年第5期13卷 516-524页

作者：楼海王椿镛王飞 Institute of Geophysics China Seismological Bureau Beijing China

The latest geopotential model, EGM96, was employed to compute the free-air gravity anomaly, geoidal separation, the average density anomalies of the crust and the uppermost mantle, and the distribution pattern of the viscous stress exerted by Mantle convection over Xinjiang and its neighboring areas. Based on these results and other data, we try to interpret the geodynamical features of the Tianshan orogen. Our research suggests that the Tianshan orogen is in a tectonic setting of compressive settling, driven by Mantle convection. Under the effect of the compressive stress field, asymmetric in north-south direction, the Tianshan orogen upheaved quickly. The center of compressive stress field is in the south of the Tianshan, and the characteristic of stress field is favorable for the view point that the Tarim plat subducts beneath the Tianshan. The southern margin of the Juggar basin and the northern margin of the Tarim basin are two areas where the crust is of mass deficiency. We attribute the mass deficiency to the fact that the crust, in both the north and the south of the Tianshan is bent downwards under the compressive stress. Our research also indicates that the density distribution patterns in the deep of the eastern Tianshan are different from those in the middle and western Tianshan. It may be explained as the results from the east-west oriented distinction of the Mantle convection.

关键词： geopotential model geoidal separation viscous stress pattern Mantle convection

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On the Numerical Modeling of the Deep mantle Water Cycle in Global-Scale mantle Dynamics:The Effects of the Water Solubility Limit of Lower mantle Minerals

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Journal of Earth Science 2017年第4期28卷 563-577页

作者： Takashi Nakagawa Department of Mathematical Science and Advanced Technology Japan Agency for Marine-Earth Science and TechnologyYokohama 236-0001Japan

Water is the most important component in Earth system evolution. Here, I review the current understanding of the fate of water in the mantle dynamics system based on high-pressure and temperature experiments, geochemical analyses, seismological and geomagnetic observations, and nu- merical modeling of both regional- and giobal-scale mantle dynamics. In addition, as a numerical ex- ample, I show that the water solubility of the deep mantle is strongly sensitive to global-scale water cir- culation in the mantle. In a numerical example shown here, water solubility maps as functions of tem- perature and pressure are extremely important for revealing the hydrous structures in both the mantle transition zone and the deep mantle. Particularly, the water solubility limit of lower mantle minerals should be not so large as ~100 ppm for the mantle transition zone to get the largest hydrous reservoir in the giobal-scale mantle dynamics system. This result is consistent with the current view of mantle water circulation provided by mineral physics, which is also found as a hydrous basaltic crust in the deep mantle and the water enhancement of the mantle transition zone simultaneously. In this paper, I also discuss some unresolved issues associated with mantle water circulation, its influence on the onset and stability of plate motion, and the requirements for developing Earth system evolution in mantle dy- namics simulations.

关键词： numerical modeling Mantle convection water cycle water solubility limit.

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