Can the Earth's crust be in a state of isostasy?

Artyushkov, E. V.

doi:10.1029/jb079i005p00741

Cited by 43 publications

(23 citation statements)

References 8 publications

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“…The models indicate that at wavelengths comparable to width of orogenic belts (<300 km), the state of isostasy may be not the asymptotic limit for the crust and that the crust may approach a state with significant overcompensation or undercompensation on the Moho, depending on crustal and lithospheric rheology. The mechanism resulting in the nonisostatic state is different from that proposed by Artyushkov [1974]. The results for the cases with an effectively elastic upper crust are consistent with those from Kusznir and Matthews [1988].…”

Section: Introductionsupporting

confidence: 81%

Dynamics of crustal compensation and its influences on crustal isostasy

Zhong¹

1997

J. Geophys. Res.

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Abstract. Deviation from isostasy is commonly believed to be caused by the strength of the Earth's lithosphere. An analysis of crustal compensation dynamics suggests that the deviation may have a dynamic origin. The analysis is based on analytic models that assume that (1) the medium is incompressible and has a layered and linear viscoelastic theology and (2) the amplitude of topography is small compared with its wavelength. The models can describe topographic relaxation of different density interfaces at both small (e.g., postglacial rebound) and large timescales. The models show that for a simple crust-mantle system with topography at the Earth's surface and Moho representing the only mass anomalies, while the crust always approaches the isostatic state at long wavelengths (>800 km), crustal isostasy may not be an asymptotic limit at short wavelengths, depending on crustal and lithospheric theology. For a crust with viscosity smaller than lithospheric viscosity, at wavelengths comparable with widths of orogenic belts (i.e., <300 km), the crust tends to approach a state with significant overcompensation (i.e., excess topography at the Moho) within a timescale of about 107 years, and this characteristic time depends on wavelengths and crustal viscosity. This overcompensation is greater for weaker crust and stronger lithosphere. A thicker crust or lithosphere also enhances this overcompensation. If crustal and lithospheric viscosities are both large and comparable, the asymptotic state for the crust displays a slight undercompensation. For an elastic and rigid upper crust, the crust eventually becomes undercompensated after a characteristic decay time of topography at the Moho. The characteristic time is dependent on viscosity and thickness of the lower crust. The deviation from isostasy arises because these viscosity structures result in a ratio of vertical velocity at the surface to vertical velocity at the Moho which in the asymptotic state for short wavelengths differs from the ratio of density contrast at the Moho to that at the surface.

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Section: Introductionsupporting

confidence: 81%

Dynamics of crustal compensation and its influences on crustal isostasy

Zhong¹

1997

J. Geophys. Res.

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“…A more speculative possibility is that the production of the initial thermal anomaly may have been localized if the region of the mid-Michigan gravity high was thick, high density, isostatically compensated crust having greater lateral tension than surrounding regions during the Ordovician (see Hinze & Merritt 1969, for gravity interpretation; Artyushkov 1973Artyushkov , 1974. Also, thicker crust would kinematically be more likely to have its thickness reduced by subcrustal processes.…”

Section: Heat Source and Loading Mechanismmentioning

confidence: 95%

Thermal Contraction and Flexure of Mid-Continent and Atlantic Marginal Basins

Sleep

Snell

1976

Geophysical Journal International

177

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Thermal contraction of the lithosphere is a probable cause of the gradual subsidence indicated by sediments of mid-continent basins and Atlantic continental shelves. The subsidence is complicated by time dependent regional isostatic compensation since adjacent parts of the lithosphere are mechanically coupled, and since creep in the lithosphere may relieve accumulated stress. Thus, if more subsidence occurs at point A than nearby point B, point A would be buoyed up and point B dragged down. Relaxation of this coupling during a later period of more gradual subsidence would produce uplift at B and downwarp at A. The absence of younger beds over local minima of subsidence such as the Florida arch, the flanks of the Michigan basin, and the Atlantic coastal plain (USA) can thus be explained. Variations in the subsidence rate due to exponential decay of the thermal anomaly or to starved basin-evaporite depositional sequences can produce observable effects.Analytic models of the Michigan basin and the Atlantic coast (USA) are compatible with previously estimated parameters: thermal decay time of the lithosphere, 50 My; flexural parameter of the lithosphere beneath air, 200 km; and viscosity of the lithosphere, poise. The effects of flexure are not clearly evident in Silurian evaporite deposition in the Michigan basin and it is probable that an extended time was required for the evaporite sequence to accumulate.The cause of the thermal heating event which precedes subsidence is unclear for mid-continent basins although bulk replacement of the uppermost mantle is necessary. The heating events may be associated with periods of slow sea-floor spreading (when slabs exert a tensional force on the lithosphere) and hence low eustatic sea level. There is little direct evidence that an initial heating event actually occurred in the Michigan basin immediately before the start of subsidence.

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“…Under such conditions, to balance the momentum of the forces acting along the lithosphere, in the gravity field, vertical deflections of the lithosphere arise from its isostatical equilibrium position (Fig. 8) (Artyushkov 1974(Artyushkov , 1983. It has been proposed that rapid, largescale changes in the depth of water in sedimentary basins occurred due to lithospheric displacements caused by changes in the forces acting along the lithosphere (Cloetingh et al 1985).…”

Section: Thermal Relaxation and Changes In The Forces Acting On The Lmentioning

confidence: 99%

“…It has been proposed that rapid, largescale changes in the depth of water in sedimentary basins occurred due to lithospheric displacements caused by changes in the forces acting along the lithosphere (Cloetingh et al 1985). Such displacements (c) are proportional to 1/L 2, where L is the characteristic width of lateral variations in lithospheric thickness (Artyushkov 1974(Artyushkov , 1983. Therefore, they are significant only in relatively narrow areas.…”

Section: Thermal Relaxation and Changes In The Forces Acting On The Lmentioning

confidence: 99%

Silurian sedimentation in East Siberia: evidence for variations in the rate of tectonic subsidence occurring without any significant sea-level changes

Artyushkov

Chekhovich

2003

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It is widely accepted that major variations of sea-level have occurred in the Phanerozoic. Third-order cycles, 1-10 Ma long with amplitudes of 20-100 m, are of special interest for geochronology and petroleum geology. The amplitude of sea-level changes in the Silurian was estimated based on highly detailed data on the East Siberian Basin, which was 2x106 km 2 in size. Fischer plots were compiled based on the thickness of 54 chronostratigraphic units -chronozones, each corresponding to a time interval c.0.5 Ma long. The synchronicity of the chronozones ensures reliable comparison of the changes occurring with time in accommodation space in different regions. The subhorizontal Fischer plots derived for several regions indicate that sea-level changes were very small in the Silurian (<5 10 m). A mathematical analysis of relative sea-level changes, which takes into account the finite rate of crustal subsidence and different possible forms of eustatic fluctuation, shows that from the observed structure of numerous Silurian successions in East Siberia, eustatic third-order sealevel changes could not have exceeded 6 20 m. In several regions of East Siberia, the rate of crustal subsidence varied as much as several hundred per cent at different times. These variations showed good similarity in form, but their amplitudes were different at different places in the basin. Most probably they were caused by variations in the rate of phase transformations in mafic rocks in the lower crust. Based on the example of the East Baltic, the absence of large-scale third-order cycles in eustatic changes of sea-level has been proven earlier for the Cambrian and earliest Ordovician. Probably, a similar situation was characteristic of many other epochs, when no large glaciations occurred, while many rapid changes of water depth in cratonic areas actually resulted from vertical crustal movements.

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Can the Earth's crust be in a state of isostasy?

Cited by 43 publications

References 8 publications

Dynamics of crustal compensation and its influences on crustal isostasy

Dynamics of crustal compensation and its influences on crustal isostasy

Thermal Contraction and Flexure of Mid-Continent and Atlantic Marginal Basins

Silurian sedimentation in East Siberia: evidence for variations in the rate of tectonic subsidence occurring without any significant sea-level changes

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