Isostatic Gravity Anomalies Research Articles

Moho Interface Modeling Beneath the Himalayas, Tibet and Central Siberia Using GOCO02S and DTM2006.0

We apply a newly developed method to estimate the Moho depths and density contrast beneath the Himalayas, Tibet and Central Siberia. This method utilizes the combined least-squares approach based on solving the inverse problem of isostasy and using the constraining information from the seismic global crustal model (CRUST2.0). The gravimetric forward modeling is applied to compute the isostatic gravity anomalies using the global geopotential model (GOCO02S) and the global topographic/ bathymetric model (DTM2006.0). The estimated Moho depths vary between 60 - 70 km beneath most of the Himalayas and Tibet and reach the maxima of ~79 km. The Moho depth under Central Siberia is typically 50 - 60 km. The Moho density contrast computed relative to the CRUST2.0 lower crustal densities has the maxima of ~300 kg m-3 under Central Tibet. It substantially decreases to 150 - 250 kg m-3 under Himalayas and north Tibet. The estimated Moho density contrast under central Siberia is within 100 - 200 kg m-3.

Reformulation of the Vening-Meinesz Moritz Inverse Problem of Isostasy for Isostatic Gravity Disturbances

The isostatic gravity anomalies have been traditionally used to solve the inverse problems of isostasy. Since gravity measurements are nowadays carried out together with GPS positioning, the utilization of gravity disturbances in various regional gravimetric applications becomes possible. In global studies, the gravity disturbances can be computed using global geopotential models which are currently available to a relatively high accuracy and resolution. In this study we facilitate the definition of the isostatic gravity disturbances in the Vening-Meinesz Moritz inverse problem of isostasy for finding the Moho depths. We further utilize uniform mathematical formalism in the gravimetric forward modelling based on methods for a spherical harmonic analysis and synthesis of gravity field. We then apply both mathematical procedures to determine globally the Moho depths using the isostatic gravity disturbances. The results of gravimetric inversion are finally compared with the global crustal seismic model CRUST2.0; the RMS fit of the gravimetric Moho model with CRUST2.0 is 5.3 km. This is considerably better than the RMS fit of 7.0 km obtained after using the isostatic gravity anomalies.

Isostatic Residual Gravity Anomaly Grid of Onshore Australia

Isostatic Residual Gravity Anomaly Grid of Onshore Australia

Small‐Scale Upper Mantle Convection Beneath the Mongolia‐Baikal Rift Zone and Its Geodynamic Significance

AbstractSmall‐scale upper mantle convection is one of the main mechanisms to control regional geodynamic processes. Some regional geodynamic processes in the Mongolia‐Baikal Rift Zone (MBRZ) are suggested to be related to the small‐scale upper mantle convection beneath the area. The aim of the present work is to study the small‐scale upper mantle convection beneath the MBRZ by gravity data, and to investigate its contribution to the regional dynamics. Based on the equations relating regional isostatic gravity anomalies and small‐scale upper mantle convection, the convection flow field beneath the MBRZ and convection‐generated stress field were investigated by using the regional isostatic gravity anomalies data. The numerical results exhibit a very complicated pattern of the mantle convection and the generated stress field, which correlates well with the regional tectonics. The mantle flow and the stress beneath the Siberia Platform and Mongolian fold belt are weak, being consistent with the current inactive tectonics in these regions. A mantle upwelling and extension stress regime is found beneath the Baikal Rift zone. The magnitude of the extension stress is low (~8 MPa), suggesting that the mantle convection is not the cause being responsible for the rifting of the Baikal rift. Mantle upwellings are also found beneath the Hangay Plateau, Altay and Gobi‐Altai, leading to extension stress in these regions. The mantle upwellings may be the mechanism responsible for the uplift of the Hangay Plateau, and the dynamic background for defining the western boundary of the Amurian Plate.

On the Character of Isostatic Equilibrium Disturbances

Summary The data of disturbances of the isostasy of the Earth’s crust and their relation to different tectonic zones give valuable information about processes in the Earth’s crust. They may be used for the evaluation of some physical parameters, for example of the asthenosphere viscosity. The last value is usually determined on the basis of the data on postglacial uplift, but there are doubts that these values can be applied to the regions with different tectonics. For this reason we have studied as a first step the character of disturbances of the isostasy in the areas of different tectonics. It was ascertained that disturbances of the isostatic equilibrium are the result of the active geotectonic process and that isostatic forces are passive as tectonic factor. In the geological time scale the readjustment takes place instantaneously, therefore isostatic anomalies of gravity may be considered as direct indications of the modern tectonic activity. Regular relations between isostatic disturbances and the character of the latest tectonic movements can be clearly revealed by the comparison of the isostatic anomalies maps with the schemes of Cenozoic crustal movements in the different tectonic zones. In particular, the antii ostatic movements of the Earth’s crust are very common features. The relations revealed between the isostatic gi avity anomalies and tectonic movements permit us to make some conclusions about the character of internal processes in the Earth. The data of isostasy are used for the evaluation of some physical parameters, characterizing the Earth’s crust state and its upper mantle. For example, for the evaluation of the asthenosphere viscosity the data are used which gives the study of Quaternary glaciations. The variety of tectonic conditions on the Earth’s surface reflects different processes taking place in the Earth’s interior and evidently shows different physical conditions. Because of this we are not sure that the results obtained from the study of isostasy in regions of glaciations (representing, as a rule, preCambrian shields) may be extrapolated on the regions differing by their tectonic positions. The results of the study of Quaternary glaciations give quite low values of the viscosity of the asthenosphere and very small times of readjustment (103-105 years). At the same time on the Earth’s surface numerous and great disturbances of equilibrium are known, manifesting in large isostatic anomalies of gravity. This fact is of great interest for an investigator. Firstly, it is very important to clear up the nature of the connection between the disturbances of isostasy and the movements of the Earth‘s crust and the change of the character of these correlations in areas of different tectonic conditions. A number of investigations has been carried out by well-known scientists: Vening Meinesz, van Bemmelen, Bullard, Lyustikh and others. On the basis of the data of isostatic gravity anomalies collected in the Institute of Physics of the Earth in Moscow an attempt was made to find basic features of isostasy in regions of different tectonics, and also the number of more particular correlations within the boundaries tectonic zones. (Artemyev 1962, 1963, 1964.)

Gravity anomaly, lithospheric structure and seismicity of Western Himalayan Syntaxis

A compiled gravity anomaly map of the Western Himalayan Syntaxis is analysed to understand the tectonics of the region around the epicentre of Kashmir earthquake of October 8, 2005 (Mw = 7.6). Isostatic gravity anomalies and effective elastic thickness (EET) of lithosphere are assessed from coherence analysis between Bouguer anomaly and topography. The isostatic residual gravity high and gravity low correspond to the two main seismic zones in this region, viz. Indus–Kohistan Seismic Zone (IKSZ) and Hindu Kush Seismic Zones (HKSZ), respectively, suggesting a connection between siesmicity and gravity anomalies. The gravity high originates from the high-density thrusted rocks along the syntaxial bend of the Main Boundary Thrust and coincides with the region of the crustal thrust earthquakes, including the Kashmir earthquake of 2005. The gravity low of HKSZ coincides with the region of intermediate–deep-focus earthquakes, where crustal rocks are underthrusting with a higher speed to create low density cold mantle. Comparable EET (∼55 km) to the focal depth of crustal earthquakes suggests that whole crust is seismogenic and brittle. An integrated lithospheric model along a profile provides the crustal structure of the boundary zones with crustal thickness of about 60 km under the Karakoram–Pamir regions and suggests continental subduction from either sides (Indian and Eurasian) leading to a complex compressional environment for large earthquakes.

Lithospheric structure in the eastern region of Mars’ dichotomy boundary

We examine gravity, topography, and magnetic field data along the well-preserved Martian dichotomy boundary between 105° and 180°E to better understand the origin and modification of the dichotomy boundary. Admittance modeling indicates bottom-loading for the Amenthes region (105–135°E) with crustal and elastic thickness estimates of 15–40 km, and 15–35 km and top-loading for the Aeolis region (145–180°E) with crustal and elastic thickness estimates of 10–20 km and 10–15 km, respectively. There is a general trend from bottom-loading in the west, to top-loading in the east. The bottom-loading signature near Amenthes may reflect its proximity to the Isidis basin or a broad valley southeast of Isidis. Surface volcanic deposits may produce the top-loading seen at Aeolis. Additional processes such as erosion and faulting have clearly affected the dichotomy and may contribute to the loading signature. Low elastic thickness estimates are consistent with loading in the Noachian, when heat flow was high. Significant Bouguer and isostatic gravity anomalies in these areas indicate substantial variations in the crustal density structure. Crater age dating indicates that major surface modification occurred early in the Noachian, and the small elastic thickness estimates also suggest that subsurface modification occurred in the Noachian. Magnetic and gravity anomalies show comparable spatial scales (several hundred kilometers). The similarity in scale and the constant ratio of the amplitudes of the isostatic and Bouguer gravity to the magnetic anomalies along the dichotomy suggest a common origin for the anomalies. Igneous intrusion and/or local thinning or thickening of the crust, possibly with a contribution from hydrothermal alteration, are the most likely mechanisms to create the observed anomalies.

Two-dimensional and three-dimensional finite element modelling of mantle processes beneath central South Island, New Zealand

SUMMARY Numerical models that include pre-existing faults, elasto‐visco‐plastic rheology, thermal structure, realistic plate boundary conditions, and surface erosion are built to investigate alternative hypotheses of mantle flow geometry beneath central South Island, New Zealand. Bouguer gravity anomalies, teleseismic traveltime delays and seismic velocity structures are used to constrain models. Model predictions are compared with topography, uplift, magnetotelluric resistivity structure, isostatic gravity anomalies (IGAs), and seismicity. We find that the wedge model, in which the mantle lithosphere of the Australia plate is wedged between crust and mantle lithosphere of the Pacific plate, gives reasonable predictions of topography, uplift rate, IGAs, and stress and strain state in the lithosphere. Coupled erosional-tectonic models suggest that tectonic compression primarily determines the asymmetric surface relief, with erosion influencing its detail and having small effects on shallow stresses. Both 2-D and 3-D models suggest that the neotectonics of central South Island is dominated by weak faults. 3-D model results show that the Alpine fault and mantle shear zone accommodate most convergent and strike-slip plate motion, confirming non-partitioned plate motion in this region. Adding the regional strike-slip component has little effect on the convergent velocity field, and only changes the stress field by rotating the horizontal principal stresses out of the plane of the cross-section.

Interseismic coupling and asperity distribution along the Kamchatka subduction zone

GPS measurements of interseismic horizontal surface velocities reveal the degree of kinematic coupling of the plate boundary thrust along the Kamchatka subduction zone from about 51° to 57°N latitude. Inversions for the distribution of aseismic slip rate along the ∼15°NW dipping underthrust suggest a nonslipping plate interface in southern Kamchatka above ∼50 km depth, along the segment that ruptured in the Mw = 9, 1952 earthquake. North of ∼53°N, the subduction interface experiences significant aseismic slip, consistent with the lower seismic moment release in M ≤ 8.5 earthquakes along this portion of the subduction zone. The GPS velocities are consistent with a boundary element forward model in which historic earthquake rupture zones are represented as locked asperities, surrounded by a zero shear stress subduction interface loaded by plate convergence. Models in which the complete rupture zones of historic earthquakes are considered locked greatly overpredict the degree of kinematic coupling. Reducing the area of the locked model asperities to the central 25% area of historic rupture zones fits the data well, suggesting that large earthquakes involve small fully locked core asperities surrounded by conditionally stable portions of the plate interface. Areas of low aseismic slip rate appear to be roughly correlated with areas of low isostatic gravity anomalies over offshore forearc basins, while less coupled portions of the Kamchatka subduction zone coincide with high‐gravity anomalies offshore of two peninsulas, possibly related to the subduction of the Emperor‐Meji seamount chain and the Kruzenstern fracture zone.

The edge of northwestern North America at ∼1.8 Ga

The ∼1.80 Ga edge of the northwestern North American craton is buried beneath Phanerozoic and Proterozoic rocks of the Western Canada Sedimentary Basin and the adjacent Cordillera. It is visible in more than eight deep seismic reflection profiles that have images of west-facing crustal-scale monoclines with up to 15–20 km of vertical relief, and it produces regional isostatic gravity anomalies that can be followed for more than 1500 km along strike. The deep reflection profiles include two major transects of Lithoprobe (southern Canadian Cordillera transect and Slave – Northern Cordillera Lithospheric Evolution (SNORCLE) transect) and industry profiles that are strategically located to provide depth and geometry constraints on the monoclines. The isostatic anomalies mark the density transition from Paleoproterozoic and older crystalline rocks of the Canadian Shield to less dense supracrustal rocks of westward-thickening late Paleo proterozoic and younger strata. These gravity anomaly patterns thus provide areal geometry of crustal structure variations along strike away from the depth control provided by the seismic data. Although many of the monoclines follow the Fort Simpson geophysical trend along the Cordilleran deformation front, isostatic anomalies near Great Bear Lake delineate a northeast-striking region of low values that may coincide with a failed rift arm or the southern margin of a large basin. The monoclines are interpreted as a series of en echelon structures that probably formed as a result of lithospheric extension at about 1.80–1.70 Ga following terminal accretion of the Paleoproterozoic Wopmay Orogen.

A new isostatic model of the lithosphere and gravity field

Based on the analysis of various factors controlling isostatic gravity anomalies and geoid undulations, it is concluded that it is essential to model the lithospheric density structure as accurately as possible. Otherwise, if computed in the ‘classical’ way (i.e. based on the surface topography and the simple Airy compensation scheme), isostatic anomalies mostly reflect differences of the real lithosphere structure from the simplified compensation model, and not necessarily the deviations from isostatic equilibrium. Starting with global gravity, topography and crustal density models, isostatic gravity anomalies and geoid undulations have been determined. The initial crust and upper-mantle density structure has been corrected in a least squares adjustment using gravity. To model the long-wavelength (>2000 km) features in the gravity field, the isostatic condition (i.e. equal mass for all columns above the compensation level) is applied in the adjustment to uncover the signals from the deep-Earth interior, including dynamic deformations of the Earth’s surface. The isostatic gravity anomalies and geoid undulations, rather than the observed fields, then represent the signals from mantle convection and deep density inhomogeneities including remnants of subducted slabs. The long-wavelength non-isostatic (i.e. the dynamic) topography was estimated to range from –0.4 to 0.5 km. For shorter wavelengths (<2000 km), the isostatic condition is not applied in the adjustment in order to obtain the non-isostatic topography due to regional deviations from classical Airy isostasy. The maximum deviations from Airy isostasy (−1.5 to 1 km) occur at currently active plate boundaries. As another result, a new global model of the lithosphere density distribution is generated. The most pronounced negative density anomalies in the upper mantle are found near large plume provinces, such as Iceland and East Africa, and in the vicinity of the mid-ocean ridge axes. Positive density anomalies in the upper mantle under the continents are not correlated with the cold and thick lithosphere of cratons, indicating a compensation mechanism due to thermal and compositional density.

Bouguer reduction density, why 2.67?

One of the most widely recognized parameters in solid-earth geophysics is the assumed density of the surface rocks of the continental crust, 2.67 g/cm 3 , or 2670 kg/m 3 in today9s preferred SI units. In the calculation of Bouguer and isostatic gravity anomalies, which are widely used for geological studies, the gravitational effect of the earth mass between an observation site and a datum is calculated assuming an infinite, flat slab of a specified density that approximates the mass. The datum for most surveys is sea level or, in the case of surveys of limited areas, it may be the elevation of the lowest station in the survey. Although the choice of datum is arbitrary, commonly sea level is used in an attempt to standardize anomalies from different surveys. Similarly, a density of 2.67 g/cm 3 is generally assumed for the density of the included mass in regional gravity surveys.

The Baikal rift zone: the effect of mantle plumes on older structure

The main chain of SW–NE-striking Cenozoic half-grabens of the Baikal rift zone (BRZ) follows the frontal parts of Early Paleozoic thrusts, which have northwestern and northern vergency. Most of the large rift half-grabens are bounded by normal faults at the northwestern and northern sides. We suggest that the rift basins were formed as a result of transformation of ancient thrusts into normal listric faults during Cenozoic extension. Seismic velocities in the uppermost mantle beneath the whole rift zone are less than those in the mantle beneath the platform. This suggests thinning of the lithosphere under the rift zone by asthenosphere upwarp. The geometry of this upwarp and the southeastward spread of its material control the crustal extension in the rift zone. This NW–SE extension cannot be blocked by SW–NE compression generated by pressure from the Indian lithospheric block against Central Asia. The geochemical and isotopic data from Late Cenozoic volcanics suggest that the hot material in the asthenospheric upwarp is probably provided by mantle plumes. To distinguish and locate these plumes, we use regional isostatic gravity anomalies, calculated under the assumption that topography is only partially compensated by Moho depth variations. Variations of the lithosphere–asthenosphere discontinuity depth play a significant role in isostatic compensation. We construct three-dimensional gravity models of the plume tails. The results of this analysis of the gravity field are in agreement with the seismic data: the group velocities of long-period Rayleigh waves are reduced in the areas where most of the recognized plumes are located, and azimuthal seismic anisotropy shows that these plumes influence the flow directions in the mantle above their tails. The Baikal rift formation, like the Kenya, Rio Grande, and Rhine continental rifts [Achauer, U., Granet, M., 1997. Complexity of continental rifts as revealed by seismic tomography and gravity modeling. In: Jacob, A.W.B., Delvaux, D., Khan, M.A. (Eds.), Lithosphere Structure, Evolution and Sedimentation in Continental Rifts. Proceedings of the IGCP 400 Meeting, Dublin, March 20–22, 1997. Institute of Advanced Studies, Dublin, pp. 161–171], is controlled by the three following factors: (i) mantle plumes, (ii) older (prerift) linear lithosphere structures favorably positioned relative to the plumes, and (iii) favorable orientation of the far-field forces.

Crustal model for the Middle East and North Africa region: implications for the isostatic compensation mechanism

We present a new 3-D crustal model for the Middle East and North Africa region that includes detailed topography, sediment thickness, and Moho depth values. The model is obtained by collecting, integrating, and interpolating reliable, published sedimentary rock thickness and Moho depth measurements in the Middle East and North Africa region. To evaluate the accuracy of the model, the 3-D gravity response of the model is calculated and compared with available observed Bouguer gravity anomalies in the region. The gravity modelling shows that the new crustal model predicts large portions of the observed Bouguer anomalies. However, in some regions, such as the Red Sea and Caspian Sea regions, where crustal structure is relatively well-determined, the residual anomalies are of the order of a few hundred milligals. Since the new crustal model results in large residual anomalies in regions where reasonably good constraints exist for the model, these large residuals cannot simply be explained by inaccuracies in the model. To analyse the cause of these residuals further we developed an isostatically compensated (Airy-type) Moho-depth model and calculated its gravity response. Isostatic gravity anomalies are in nearly perfect agreement with the observed gravity values. However, the isostatic model differs significantly from the new (3-D) crustal model. If isostasy is to be maintained, crustal and/or upper mantle lateral density variations are needed to explain the large observed gravity residuals.

Segmentation in gravity and magnetic anomalies along the U.S. East Coast passive margin: Implications for incipient structure of the oceanic lithosphere

Segmentation is a characteristic feature of seafloor spreading along the global mid‐ocean ridge system. While segmentation of active spreading centers has been the focus of much recent research, the process by which a rifted continental margin develops into a segmented mid‐ocean ridge is still poorly understood. In this study we investigate the segmentation character of the U.S. East Coast margin through a modeling study of the margin basement structure, magnetics, and gravity anomalies. The East Coast margin is of particular interest because it is one of several rifted continental margins that display thick sequences of high seismic velocity igneous crust, presumably formed during rifting. The East Coast Magnetic Anomaly (ECMA), a distinct total field magnetic high running offshore along the margin, is commonly located seaward of the thickest sections of the high‐velocity crust and displays segmentation on length scales (100–120 km) similar to the segmentation observed at the Mid‐Atlantic Ridge (MAR). Isostatic gravity anomalies were calculated by removing from free‐air gravity the predicted effects of seafloor, sediments, and a crust‐mantle model assuming local isostatic compensation. The resultant residuals show a corridor of high anomaly running along the margin, situated close to the maximum thickness of the high seismic velocity crust as determined from the two available seismic refraction lines. Reduction to the pole (R‐T‐P) of the total field magnetic anomaly shows that after the removal of skewness from the ECMA, the location of the isostatic gravity high is closely correlated to the ECMA. The isostatic gravity high is also segmented but in two distinct wave bands: 100–150 km and 300–500 km. The short‐wavelength (100–150 km) segmentation in the R‐T‐P magnetic and isostatic gravity anomalies is similar in wavelength to segmentation in magnetization and mantle Bouguer anomaly observed along the present‐day MAR. The 300–500 km segmentation in the along‐margin isostatic gravity anomaly is similar in length scale to both intermediate‐wavelength tectonic segmentation observed in the South Atlantic and variations in lithospheric strength observed along the African margin. Furthermore, two of the intermediate‐wavelength (300–500 km) isostatic gravity lows correspond to the early traces of the Kane and Atlantis fracture zones, suggesting that these two fracture zones may define boundaries of a single tectonic corridor in the North Atlantic. We hypothesize that the direct cause of the intermediate‐wavelength segmentation may be along‐margin variations in both the amount of underplated igneous crust and the strength of the lithosphere, although the relative importance of these two effects remains unresolved. Our results imply that segmentation is an important feature of margin development and that segmentation at mature oceanic spreading centers may be directly linked to segmentation during continental rifting.

MOHO DEPTHS VERSUS GRAVITY ANOMALIES

Isostatic gravity anomalies are the best suited anomalies for different geodetic applications, such as the interpolation and the geoid determination. Different isostatic hypothesis are discussed and used to compute the depths of the Mohorovic˘ié discontinuity (Moho depths). Isostatic anomalies are then computed using different isostatic hypothesis. Comparison among the different kinds of the gravity anomalies and their empirical covariance functions are made. Vening Meinesz isostatic model gives, more or less, realistic Moho depths. Both Airy-Heiskanen and Vening Meinesz isostatic models give nearly the same isostatic anomalies. Computing the Vening Meinesz Moho depths, and hence the Vening Meinesz isostatic anomalies, is a time-consuming task. Therefore, if the isostatic anomalies are the main goal of the computation, one may easily use the better known Airy-Heiskanen isostatic model.

MOHO DEPTHS VERSUS GRAVITY ANOMALIES

Isostatic gravity anomalies are the best suited anomalies for different geodetic applications, such as the interpolation and the geoid determination. Different isostatic hypothesis are discussed and used to compute the depths of the Mohorovic˘ié discontinuity (Moho depths). Isostatic anomalies are then computed using different isostatic hypothesis. Comparison among the different kinds of the gravity anomalies and their empirical covariance functions are made. Vening Meinesz isostatic model gives, more or less, realistic Moho depths. Both Airy-Heiskanen and Vening Meinesz isostatic models give nearly the same isostatic anomalies. Computing the Vening Meinesz Moho depths, and hence the Vening Meinesz isostatic anomalies, is a time-consuming task. Therefore, if the isostatic anomalies are the main goal of the computation, one may easily use the better known Airy-Heiskanen isostatic model.

Gross differences between two isostatic gravity anomaly maps of China

Comparison of the 1° × 1° Isostatic Gravity Anomaly Map of China in the Lithosphere Dynamics Atlas of China, International Lithosphere Committee Publication No. 125 with the Isostatic Gravity Anomaly Map of China in the Atlas of Geophysics of China, International Lithosphere Committee Publication No. 201, shows that there are quite substantial differences between the two maps.

Upper mantle flow beneath the Northwest of China and its lithospheric dynamics

The regional isostatic gravity anomalies in the Northwest of China (80°–95°E, 35°–45°N) and corresponding problems of mantle dynamics are discussed in detail in this paper. It is assumed that the anomaly of isostatic gravity in this region is caused by the nonuniformity in density and that the boundary deformation is related to the thermal convection in the upper mantle. Using the correlation equation between the mantle flow and regional anomalies of isostatic gravity as a constraint, we have calculated the patterns of upper mantle convection. The result shows that the regional lithospheric tectonics is strongly correlated with the upper mantle flow. The uplift of the Tianshan and Kunlun Mountains corresponds to the upward flows in the mantle while the depression of the Tarim, Turpan and Junggar Basins corresponds to the downward flow. Meanwhile, we have also worked out a basic framework for the lithospheric dynamics of the Northwest of China. It is reasonable to infer that the mantle flow and the horizontal compression from the India plate may act as the main driving forces for the lithospheric tectonics of this region.

The upper mantle flow beneath the North China Platform

In this paper we establish an upper mantle convection model which is constrained by regional isostatic gravity anomalies. Comparing the computed convection patterns with the tectonic features of the North China Platform we find that there are two positive anomaly centers connected with upward flows. These anomalies belong to the tectonic units of the Shan-Xi geoanticline and the Lu-Xi geoanticline. The centers of downward flows are connected with the tectonic units of the Liao-Ji geosyncline. It is reasonable to suggest that the upward mantle flows push the lithosphere upward and generate the observed positive isostatic gravity anomaly. The downward mantle flows pull the lithosphere down and generate the negative anomaly. However, the use of simple analysis makes it difficult to explain the complex lithospheric dynamics of this region. In order to understand lithospheric structures and tectonic features we must investigate the mechanical properties of the lithosphere and the relationship between the lithosphere and the mantle. These problems are discussed in the last section of this paper.