Upper mantle <i>S</i> velocity structure of North America

Lee, S. van der; Nolet, Guust

doi:10.1029/97jb01168

Cited by 346 publications

(308 citation statements)

References 69 publications

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“…Moreover, recent analyses of xenolith P-T data suggest that the intersection between the craton geotherm and the mantle adiabat occurs between depths of 160 and 300 km, with a best estimate in the range of 220-250 km beneath the cratons Rudnick & Nyblade 1999). These estimates are entirely consistent with our results, which show that positive velocity perturbations beneath the cratons extend to depths of at least 250-300km, and with results from other detailed regional seismic studies (VanDecar et al 1995;Van der Lee & Nolet 1997;Ritsema et al 1998;Ritsema & van Heijst 2000).…”

Section: Tectospheric Rootssupporting

confidence: 82%

“…These refi'actory roots extend into the mantle to depths of at least 200 km and perhaps more (e.g. Jordan 1975;Lerner-Lam & Jordan 1987; Van der Lee & Nolet 1997;Jaupart & Mareschal 1999;Rudnick & Nyblade 1999;Shapiro et al 1999;Zhao et al 1999;Ritsema & van Heijst 2000;James et al 2001b). The tectosphere is characterized by low heat flow (Jones 1988) and a very low geothermal gradient relative to Proterozoic mantle Jaupart & Mareschal 1999;Nyblade 1999;Rudnick & Nyblade 1999).…”

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confidence: 99%

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Formation and evolution of Archaean cratons: insights from southern Africa

James

Fouch

2002

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Archaean cratons are the stable remnants of Earth's early continental lithosphere, and their structure, composition and survival over geological time make them unique features of the Earth's surface. The Kaapvaal Project of southern Africa was organized around a broadly diverse scientific collaboration to investigate fundamental questions of craton formation and mantle differentiation in the early Earth. The principal aim of the project was to characterize the physical and chemical nature of the crust and mantle of the cratons of southern Africa in geological detail, and to use the 3D seismic and geochemical images of crustal and mantle heterogeneity to reconstruct the assembly history of the cratons. Seismic results confirm that the structure of crust and tectospheric mantle of the cratons differs significantly from that of post-Archaean terranes. Three-dimensional body-wave tomographic images reveal that high-velocity mantle roots extend to depths of at least 200 kin, and locally to depths of 250 300 km beneath cratonic terranes. No low-velocity channel has been identified beneath the cratonic root. The Kaapvaal Craton was modified approximately 2.05Ga by the Bushveld magmatic event, and the mantle beneath the Bushveld Province is characterized by relatively low seismic velocities. The crust beneath undisturbed Archaean craton is relatively thin (c. 35-40km), unlayered and characterized by a strong velocity contrast across a sharp Moho, whereas post-Archaean terranes and Archaean regions disrupted by large-scale Proterozoic magmatic or tectonic events are characterized by thicker crust, complex Moho structure and higher seismic velocities in the lower crust. A review of Re Os depletion model age determinations confirms that the mantle root beneath the cratons is Archaean in age. The data show also that there is no apparent age progression with depth in the mantle keel, indicating that its thickness has not increased over geological time. Both laboratory experiments and geochemical results from eclogite xenoliths suggest that subduction processes played a central role in the formation of Archaean crust, the melt depletion of Archaean mantle and the assembly of early continental lithosphere. Co-ordinated geochronological studies of crustal and mantle xenoliths have revealed that both crust and mantle have experienced a multi-stage history. The lower crust in particular retains a comprehensive record of the tectonothermal evolution of the lithosphere. Analysis of lower-crustal xenoliths has shown that much of the deep craton experienced a dynamic and protracted history of tectonothermal activity that is temporally associated with events seen in the surface record. Cratonization thus occurred not as a discrete event, but in stages, with final stabilization postdating crustal formation.

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Section: Tectospheric Rootssupporting

confidence: 82%

mentioning

confidence: 99%

Formation and evolution of Archaean cratons: insights from southern Africa

James

Fouch

2002

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“…of mantle xenoliths from kimberlites also point to a low geothermal gradient and a thick lithosphere (e.g., Boyd et al, 1985). Recently, seismic tomography surveys have shown deep continental roots characterized by high seismic wave velocity, probably due to lower upper mantle temperatures, beneath cratonic domains (Grand, 1994;Polet and Anderson, 1995;Van der Lee and Nolet, 1997). This suggests that cratonic blocks have cold geotherms and, therefore, a high stiffness (Fig.…”

Section: Development Of Stiff Heterogeneities: Aging Of the Continentmentioning

confidence: 99%

Rheological heterogeneity, mechanical anisotropy and deformation of the continental lithosphere

1998

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This paper aims to present an overview on the influence of rheological heterogeneity and mechanical anisotropy on the deformation of continents. After briefly recapping the concept of rheological stratification of the lithosphere, we discuss two specific issues: (1) as supported by a growing body of geophysical and geological observations, crust=mantle mechanical coupling is usually efficient, especially beneath major transcurrent faults which probably crosscut the lithosphere and root within the sublithospheric mantle; and (2) in most geodynamic environments, mechanical properties of the mantle govern the tectonic behaviour of the lithosphere. Lateral rheological heterogeneity of the continental lithosphere may result from various sources, with variations in geothermal gradient being the principal one. The oldest domains of continents, the cratonic nuclei, are characterized by a relatively cold, thick, and consequently stiff lithosphere. On the other hand, rifting may also modify the thermal structure of the lithosphere. Depending on the relative stretching of the crust and upper mantle, a stiff or a weak heterogeneity may develop. Observations from rift domains suggest that rifting usually results in a larger thinning of the lithospheric mantle than of the crust, and therefore tends to generate a weak heterogeneity. Numerical models show that during continental collision, the presence of both stiff and weak rheological heterogeneities significantly influences the large-scale deformation of the continental lithosphere. They especially favour the development of lithospheric-scale strike-slip faults, which allow strain to be transferred between the heterogeneities. An heterogeneous strain partition occurs: cratons largely escape deformation, and strain tends to localize within or at the boundary of the rift basins provided compressional deformation starts before the thermal heterogeneity induced by rifting are compensated. Seismic and electrical conductivity anisotropies consistently point towards the existence of a coherent fabric in the lithospheric mantle beneath continental domains. Analysis of naturally deformed peridotites, experimental deformations and numerical simulations suggest that this fabric is developed during orogenic events and subsequently frozen in the lithospheric mantle. Because the mechanical properties of single-crystal olivine are anisotropic, i.e. dependent on the orientation of the applied forces relative to the dominant slip systems, a pervasive fabric frozen in the mantle may induce a significant mechanical anisotropy of the whole lithospheric mantle. It is suggested that this mechanical anisotropy is the source of the so-called tectonic inheritance, i.e. the systematic reactivation of ancient tectonic directions; it may especially explain preferential rift propagation and continental break-up along pre-existing orogenic belts. Thus, the deformation of continents during orogenic events results from a trade-off between tectonic forces applied at plate boundaries, plate geometry,...

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“…The tomographic evidence (van _ der _ Lee & Nolet, 1997) indicates that the temperature at 110 km depth beneath the part of the Appalachians with the lowest heatflow is ~1200 °C. This is much less than would be predicted from the aforementioned extrapolation but could be accommodated instead with a more complex crustal model.…”

Section: Et _ Al 2002) the Penokean Province Is Bounded To The Wesmentioning

confidence: 99%

Relation between alternations of uplift and subsidence revealed by Late Cenozoic fluvial sequences and physical properties of the continental crust

Westaway

Bridgland

2014

Boreas

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Upper mantle S velocity structure of North America

Cited by 346 publications

References 69 publications

Formation and evolution of Archaean cratons: insights from southern Africa

Formation and evolution of Archaean cratons: insights from southern Africa

Rheological heterogeneity, mechanical anisotropy and deformation of the continental lithosphere

Relation between alternations of uplift and subsidence revealed by Late Cenozoic fluvial sequences and physical properties of the continental crust

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