A gravity model of the North Eurasia crust and upper mantle: 1. Mantle and isostatic residual gravity anomalies

abstract Arrays of seismographs are usually considered to be detectors which give enhanced signals from distant earthquakes. They also provide, however, a new way of learning more about the structure of the crust and upper mantle. The deviation of the seismic-wave surface from its expected configuration may be regarded as a consequence of non-homogeneous and anisotropic conditions in the earth. The operations of the University of California network of telemetry stations in the Coast Ranges of California provides an opportunity to discover the practicality of this approach. The situation of this network near the continental margin gives the study particular interest. The differences in arrival-times between array elements of coherent peaks or troughs of P and pP phases from 28 teleseisms in the period of 1963-1964 were read from the telemetry records of the central California seismographic array. The direction of approach and velocities of the wave fronts were then determined and compared with the great circle azimuths and with the apparent velocities calculated from the Jeffreys-Bullen tables. The observed anomalies in direction of approach and apparent velocites are found to be cyclic functions of the direction of the source. The amplitudes of these functions are almost 10 degrees in azimuth anomaly and 1.0 sec/deg in slowness anomaly. Error analyses show that the anomaly functions cannot be attributed to the measurement errors. The derived anomaly functions provide a powerful means of examining crustal and upper mantle structure under the array and perhaps at the source. Variations between subsets of the array indicate significant differences in structure between portions of the Coast Ranges to the north and to the south of Hollister.

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An integrated gravity model for Europe's crust and upper mantle

Earth and Planetary Science Letters ◽

10.1016/j.epsl.2010.04.041 ◽

2010 ◽

Vol 296 (3-4) ◽

pp. 195-209 ◽

Cited By ~ 35

Author(s):

M.K. Kaban ◽

M. Tesauro ◽

S. Cloetingh

Keyword(s):

Gravity Model ◽

Upper Mantle ◽

Crust And Upper Mantle

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Crust-mantle velocity structure in Shanxi rift, Central North China Craton

10.5194/egusphere-egu2020-20659 ◽

2020 ◽

Author(s):

Yan Cai ◽

Jianping Wu

Keyword(s):

Upper Mantle ◽

High Velocity ◽

North China Craton ◽

Lower Crust ◽

North China ◽

Velocity Structure ◽

Low Velocity ◽

Crust And Upper Mantle ◽

The North ◽

Shanxi Rift

North China Craton is the oldest craton in the world. It contains the eastern, central and western part. Shanxi rift and Taihang mountain contribute the central part. With strong tectonic deformation and intense seismic activity, its crust-mantle deformation and deep structure have always been highly concerned. In recent years, China Earthquake Administration has deployed a dense temporary seismic array in North China. With the permanent and temporary stations, we obtained the crust-mantle S-wave velocity structure in the central North China Craton by using the joint inversion of receiver function and surface wave dispersion. The results show that the crustal thickness is thick in the north of the Shanxi rift (42km) and thin in the south (35km). Datong basin, located in the north of the rift, exhibits large-scale low-velocity anomalies in the middle-lower crust and upper mantle; the Taiyuan basin and Linfen basin, located in the central part, have high velocities in the lower crust and upper mantle; the Yuncheng basin, in the southern part, has low velocities in the lower crust and upper mantle velocities, but has a high-velocity layer below 80 km. We speculate that an upwelling channel beneath the west of the Datong basin caused the low velocity anomalies there. In the central part of the Shanxi rift, magmatic bottom intrusion occurred before the tension rifting, so that the heated lithosphere has enough time to cool down to form high velocity. Its current lithosphere with high temperature may indicate the future deformation and damage. There may be a hot lithospheric uplift in the south of the Shanxi rift, heating the crust and the lithospheric mantle. The high-velocity layer in its upper mantle suggests that the bottom of the lithosphere after the intrusion of the magma began to cool down.

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Thermodynamic evolution of lithosphere of the North China craton: Records from lower crust and upper mantle xenoliths from Hannuoba

Chinese Science Bulletin ◽

10.1360/03wd0133 ◽

2003 ◽

Vol 48 (21) ◽

pp. 2371 ◽

Cited By ~ 15

Author(s):

Yongsheng LIU

Keyword(s):

Upper Mantle ◽

North China Craton ◽

Lower Crust ◽

North China ◽

Mantle Xenoliths ◽

Crust And Upper Mantle ◽

The North

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CRUST AND UPPER MANTLE IN THE ZONE OF JUNCTION BETWEEN THE CENTRAL ASIAN AND PACIFIC FOLD BELTS

Tikhookeanskaya Geologiya ◽

10.30911/0207-4028-2021-40-5-16-32 ◽

2021 ◽

Vol 40 (5) ◽

pp. 16-32

Author(s):

A.M. Petrishchevsky ◽

Keyword(s):

Upper Mantle ◽

Deep Structure ◽

Sedimentary Basins ◽

Density Contrast ◽

Tectonic Structures ◽

Crust And Upper Mantle ◽

North East ◽

The North ◽

The Pacific ◽

Amurian Plate

Spatial distributions of gravity sources and density contrast of geological media, which is reflected by the values of parameter μz , into the crust and upper mantle of Northeast China are analyzed. Features of rheological layering of the tectonosphere and deep spatial relationships of tectonic structures (cratonic blocks, marginal terranes, and sedimentary basins) are defined. In the density contrast distributions the formal signs of Paleozoic subduction of the North-China Craton and Mesozoic subduction of the Pacific Plate under the Amurian Plate were revealed. Crustal deformations are in sharp contrast with upper mantle deformations in structural planes resulting from different directions of tectonic stresses in the Paleozoic and Mesozoic. Thrusting of marginal terranes (Jamusi, Khanka) over the Amurian Plate lithosphere is revealed. Rheology and deep structure of North East China bear many similarities to other regions of the Pacific western margin in Asia and Australia.

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GEOPHYSICAL STUDIES AND TECTONISM OF THE HELLENIDES

Bulletin of the Geological Society of Greece ◽

10.12681/bgsg.11158 ◽

2017 ◽

Vol 43 (1) ◽

pp. 32 ◽

Cited By ~ 1

Author(s):

J. Makris

Keyword(s):

Upper Mantle ◽

Aegean Sea ◽

Velocity Model ◽

Normal Faults ◽

Tectonic Deformation ◽

Flow Density ◽

Crust And Upper Mantle ◽

The North ◽

Deep Seismic Soundings ◽

Western Greece

By constraining gravity modelling by Deep Seismic Soundings (DSS) and the Bouguer gravity field of Greece a 3-D density-velocity model of the crust and upper mantle was developed. It was shown that in the north Aegean Trough and the Thermaikos Basins the sediments exceed 7 km in thickness. The basins along the western Hellenides and the coastal regions of western Greece are filled with sediments of up to 10 km thickness, including the Prepulia and Alpine metamorphic limestones. The thickest sedimentary series however, were mapped offshore southwest and southeast of Crete and are of the order of 12 to 14 km. The crust along western Greece and the Peloponnese ranges between 42 and 32 km thickness while the Aegean region is floored by a stretched continental crust varying between 24 to 26 km in the north and eastern parts and thins to only 16 km at the central Cretan Sea. The upper mantle below the Aegean Sea is occupied by a lithothermal system of low density (3.25 gr/cm³) and Vp velocity (7.7 km/s), which is associated with the subducted Ionian lithosphere below the Aegean Sea. Isostasy is generally maintained at crustal and subcrustal levels except for the compressional domain of western Greece and the transition between the Mediterranean Ridge and the continental backstop. The isotherms computed from the Heat Flow density data and the density model showed a significant uplift of the temperature field below the Aegean domain. The 400°C isotherm is encountered at less than 10 Km depth. Tectonic deformation is controlled by dextral wrench faulting in the Aegean domain, while western Greece is dominated by compression and crustal shortening. Strike-slip and normal faults accommodate the western Hellenic thrusts and the westwards sliding of the Alpine napes, using the Triassic evaporates as lubricants.

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Constraining dynamic models in North America using the static gravity field

10.5194/egusphere-egu2020-6964 ◽

2020 ◽

Author(s):

Jesse Reusen ◽

Bart Root ◽

Javier Fullea ◽

Zdenek Martinec ◽

Wouter van der Wal

Keyword(s):

Gravity Anomaly ◽

Gravity Field ◽

Upper Mantle ◽

Lower Mantle ◽

Mantle Convection ◽

Dynamic Models ◽

Gravity Anomalies ◽

Mantle Flow ◽

Seismic Velocities ◽

Crust And Upper Mantle

The negative anomaly present in the static gravity field near Hudson Bay bears striking resemblance to the area depressed by the Laurentide ice sheet during the Last Glacial Maximum, suggesting that it is at least partly due to Glacial Isostatic Adjustment (GIA), but mantle convection and density anomalies in the crust and the upper mantle are also expected to contribute. At the moment, the contribution of GIA to this anomaly is still disputed. Estimates, which strongly depend on the viscosity of the mantle, range from 25 percent to more than 80 percent. Our objective is to find the contributions from GIA and mantle convection, after correcting for density anomalies in the topography, crust and upper mantle. The static gravity field has the potential to constrain the viscosity profile which is the most uncertain parameter in GIA and mantle convection models. A spectral method is used to transform 3D spherical density models of the crust into gravity anomalies. Density anomalies in the lithosphere are estimated so that isostatic compensation is reached at a depth of 300 km. The dynamic processes of mantle flow are corrected for before isostasy is assumed. Upper and lower mantle viscosities are varied so that the gravity anomaly predicted from the dynamic models matches the residual gravity anomaly. We consider uncertainties due to the crustal model, the lithosphere-asthenosphere boundary (LAB), the conversion from seismic velocities to density and the ice history used in the GIA model. The best fit is found for lower mantle viscosities >1022 Pa s.

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