Geodynamic Evidence for a Chemically Depleted Continental Tectosphere

Forte, A. M.; Perry, Heidi

doi:10.1126/science.290.5498.1940

Cited by 152 publications

(168 citation statements)

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“…This is consistent with analyses of mineral physics data, which show that at shallow depths in the mantle, seismic velocities are generally much less sensitive to composition than to variations in temperature [Deschamps et al, 2002;Cammarano et al, 2003]. However, chemical depletion of subcontinental lithosphere [e.g., the tectosphere hypothesis of Jordan, 1975] can lead to small detectable changes in wave speeds identifiable by considering decorrelations between P-and S-wave tomography [Goes et al, 2000], combined tomography and gravity data [Forte and Perry, 2000;Deschamps et al, 2002;van Gerven et al, 2004] and seismic anisotropy [Beghein and Trampert, 2004].…”

Section: Origin Of Wave Speed Anomalies: Demise Of the Thermal Paradigmsupporting

confidence: 69%

Towards a quantitative interpretation of global seismic tomography

Trampert

Hilst

2005

Geophysical Monograph Series

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We review the success of seismic tomography in delineating spatial variations in the propagation speed of seismic waves on length scales from several hundreds to many thousands of kilometers. In most interpretations these wave speed variations are thought to reflect variations in temperature. Careful consideration of shear wave, bulk sound, and, most recently, density variations is, however, producing increasingly compelling evidence for chemical heterogeneity (that is, spatial variations in bulk major element composition) having a first-order effect on the lateral variations in mass density and elasticity of the mantle. This has profound consequences for our understanding of mantle dynamics and the thermochemical evolution of our planet. We argue that the quantitative integration of constraints from seismology, mineral physics, and geodynamics, which underlies the inference of thermochemical parameters, requires careful uncertainty analyses and should move away from emphasizing visually pleasing images and single, nonunique solutions.

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Section: Origin Of Wave Speed Anomalies: Demise Of the Thermal Paradigmsupporting

confidence: 69%

Towards a quantitative interpretation of global seismic tomography

Trampert

Hilst

2005

Geophysical Monograph Series

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“…Details of shallow mantle structure are also not 8 -4 obtained from studies of the deflection of plumes by flow in the mantle [Steinberger and O'Connell, 1998]. Forte and Perry [2000] and Forte and Mitrovica [2001], however, find a pronounced viscosity minimum in the seismic low-viscosity zone using combined tomographic and geodynamic models. Richards et al [2002] point out that a shallow lowviscosity zone enhances plate-like behavior.…”

Section: Constraints From Geodynamic Modelingmentioning

confidence: 99%

“…This supports the conclusion drawn from xenolith data that cratonal lithosphere approached its present thickness a long time ago. Further quantification, which is not attempted in this paper, would require a sophisticated treatment of the effects of plate tectonics, plumes, and lower mantle density structure on geoid, elevation, and plate stresses [see Forte and Perry, 2000].…”

Section: Geoid and Intraplate Stressmentioning

confidence: 99%

“…The viscosity along the present adiabat is constant at 10 20 Pa s above 120 km depth; decreases 2 orders of magnitude between 120 and 220 km depth, increases 3 orders of magnitude between 220 and 320 km depth, and is constant at 10 21 Pa s below that. This is a simple version of the viscosity model by Forte and Perry [2000] calibrated to get the base of the lithosphere at $200 km. The intent of the viscosity increase is to impose a middle mantle viscosity compatible with glacial rebound data and to follow Forte and Perry [2000].…”

Section: Parameterized Convection With Weak Basal Dragmentioning

confidence: 99%

“…This is a simple version of the viscosity model by Forte and Perry [2000] calibrated to get the base of the lithosphere at $200 km. The intent of the viscosity increase is to impose a middle mantle viscosity compatible with glacial rebound data and to follow Forte and Perry [2000]. This region is beneath the boundary layer and has little effect on the heat flow.…”

Section: Parameterized Convection With Weak Basal Dragmentioning

confidence: 99%

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Survival of Archean cratonal lithosphere

2003

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[1] I use thermal convection models to search for combinations of physical parameters that are compatible with the results of xenolith studies on the history and present thermal structure of cratonal lithosphere. The cratonal lithosphere above $180 km depth formed in the Archean and remained stable until recently sampled. The mantle adiabat cooled $150 K over this time. The temperature change across the rheologically active boundary layer at the lithospheric base is <300 K over a depth range of several tens of kilometers. Modern cratonal lithospheric thicknesses are relatively uniform, $225 km, much thicker than old oceanic lithosphere. Cratonal lithosphere is now in quasi-steady state with conductive heat flow to the surface in balance with heat supplied to the base of the lithosphere by convection driven by local temperature contrasts within the rheologically active boundary layer. This heat flow and the lithosphere thickness changed little after the cratonal lithosphere stabilized. One possibility is that chemically buoyant lithosphere forms a conductive lid above the convecting normal mantle. To survive, the chemical lithosphere also needs to be more viscous than normal mantle. A reasonable situation has chemical lithosphere a factor of 20 more viscous than normal mantle with weakly temperature-dependent viscosity (a factor of e over 100 K) from 0.2 Â 10 20 Pa s along the modern mantle adiabat. However, a chemical lid is unnecessary for lithospheric thickness to change slowly over time. For example, the base of the lithosphere may be stable if the viscosity at its base (along an adiabat) decreases rapidly with depth.

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Hydration of marginal basins and compositional variations within the continental lithospheric mantle inferred from a new global model of shear and compressional velocity

et al. 2015

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We present a new global model of shear and compressional wave speeds for the entire mantle, partly based on the data set employed for the shear velocity model savani. We invert Rayleigh and Love surface waves up to the sixth overtone in combination with major P and S body wave phases. Mineral physics data on the isotropic δlnVS/δlnVP ratio are taken into account in the form of a regularization constraint. The relationship between VP and VS that we observe in the top 300 km of the mantle has important thermochemical implications. Back‐arc basins in the Western Pacific are characterized by large VP/VS and not extremely low VS at ∼150 km depth, consistently with presence of water. Most pronounced anomalies are located in the Sea of Japan, in the back‐arc region of the Philippine Sea, and in the South China Sea. Our results indicate the effectiveness of slab‐related processes to hydrate the mantle and suggest an important role of Pacific plate subduction also for the evolution of the South China Sea. We detect lateral variations in composition within the continental lithospheric mantle. Regions that have been subjected to rifting, collisions, and flood basalt events are underlain by relatively large VP/VS ratio compared to undeformed Precambrian regions, consistently with a lower degree of chemical depletion. Compositional variations are also observed in deep lithosphere. At ∼200 km depth, mantle beneath Australia and African cratons has comparable positive VS anomalies with other continental regions, but VP is ∼1% higher.

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Geodynamic Evidence for a Chemically Depleted Continental Tectosphere

Cited by 152 publications

References 23 publications

Towards a quantitative interpretation of global seismic tomography

Towards a quantitative interpretation of global seismic tomography

Survival of Archean cratonal lithosphere

Hydration of marginal basins and compositional variations within the continental lithospheric mantle inferred from a new global model of shear and compressional velocity

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