Stabilisation of Archaean lithospheric mantle: A ReOs isotope study of peridotite xenoliths from the Kaapvaal craton

Pearson, D.G.; Carlson, Richard W.; Shirey, Steven B.; Boyd, F. R.; Nixon, P.H.

doi:10.1016/0012-821x(95)00125-v

Cited by 420 publications

(207 citation statements)

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“…Although the tectosphere hypothesis of deep, cold, and chemically distinct keels beneath Okal & Anderson 1975;Anderson 1979;Sclater et al 1980), the model has gained widespread acceptance, buttressed by petrological and geochemical studies of mantle xenoliths, particularly those from southern Africa. Notable among these studies are Re-Os age determinations that show that mantle nodules erupted from even the greatest depths beneath the craton (about 200 km) are of Archaean age (Pearson et al 1995;Carlson et al 2000). 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).…”

Section: Tectospheric Rootsmentioning

confidence: 99%

“…The rocks that make up the bulk of the tectospheric mantle are highly depleted peridotites. The sheared nodules formerly believed to be enriched are now known to be depleted peridotites that were heavily metasomatized shortly before eruption (Pearson et al 1995;Carlson et al 2000). Although it is possible that metasomatized rocks are widespread in the deep cratonic mantle, pervasive metasomatism would significantly reduce seismic velocities, which is not observed in the seismic data.…”

Section: Tectospheric Rootsmentioning

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 Rootsmentioning

confidence: 99%

Section: Tectospheric Rootsmentioning

confidence: 99%

Formation and evolution of Archaean cratons: insights from southern Africa

James

Fouch

2002

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“…Moreover, most of the cratons became stable during Archean (2500-3750 Ma) 53,54 , when mantle heat flux was higher to support more vigorous convection 55 . There could be two end-member solutions to this problem 56 : (a) either cratons could resist deformation, or (b) they were avoided by the deforming agent (like mantle convection).…”

Section: Stability Of Cratonsmentioning

confidence: 99%

Understanding Deep Earth Dynamics:A Numerical Modelling Approach

Singh¹,

Agrawal²,

Ghosh³

2017

Current Science

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Enhancement in computing power and better data availability have paved the way for deciphering the earth's deeper dynamics and have provided viable explanations for various surface phenomena. Tools such as seismic tomography, numerical modelling and geophysical observations such as stresses, gravity anomalies, heat flow, etc. have helped us in addressing the mechanisms of plate driving forces, anomalous geoid variations, cratonic stability, topographic support, intraplate earthquakes and similar outstanding issues in geodynamics. Due to lack of direct observations from deep earth, numerical modelling has aided considerably in learning about subsurface processes. With better algorithms being developed everyday, it is the right time to tap their potential to push the frontiers of human knowledge.

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“…A wealth of seismological studies have investigated the structure of the Kaapvaal craton aiming at unraveling the thermal structure, the composition, and the deformation fabric of the cratonic root and at understanding the causes of its stability since Archean times, as inferred from Re-Os model ages obtained in kimberlite-born mantle xenoliths (Pearson et al, 1995). Tomographic models and receiver function data agree on the presence of a high velocity upper mantle lid Published by Copernicus Publications on behalf of the European Geosciences Union.…”

Section: Introductionmentioning

confidence: 99%

Petrophysical constraints on the seismic properties of the Kaapvaal craton mantle root

Baptiste

Tommasi

2014

Solid Earth

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Abstract.We calculated the seismic properties of 47 mantle xenoliths from 9 kimberlitic pipes in the Kaapvaal craton based on their modal composition, the crystal-preferred orientations (CPO) of olivine, ortho-and clinopyroxene, and garnet, the Fe content of olivine, and the pressures and temperatures at which the rocks were equilibrated. These data allow constraining the variation of seismic anisotropy and velocities within the cratonic mantle. The fastest P and S 2 wave propagation directions and the polarization of fast split shear waves (S 1 ) are always subparallel to olivine [100] axes of maximum concentration, which marks the lineation (fossil flow direction). Seismic anisotropy is higher for high olivine contents and stronger CPO. Maximum P wave azimuthal anisotropy (AV p ) ranges between 2.5 and 10.2 % and the maximum S wave polarization anisotropy (AV s ), between 2.7 and 8 %. Changes in olivine CPO symmetry result in minor variations in the seismic anisotropy patterns, mainly in the apparent isotropy directions for shear wave splitting. Seismic properties averaged over 20 km-thick depth sections are, therefore, very homogeneous. Based on these data, we predict the anisotropy that would be measured by SKS, Rayleigh (S V ) and Love (S H ) waves for five endmember orientations of the foliation and lineation. Comparison to seismic anisotropy data from the Kaapvaal shows that the coherent fast directions, but low delay times imaged by SKS studies, and the low azimuthal anisotropy with with the horizontally polarized S waves (S H ) faster than the vertically polarized S wave (S V ) measured using surface waves are best explained by homogeneously dipping (45 • ) foliations and lineations in the cratonic mantle lithosphere. Laterally or vertically varying foliation and lineation orientations with a dominantly NW-SE trend might also explain the low measured anisotropies, but this model should also result in backazimuthal variability of the SKS splitting data, not reported in the seismological data. The strong compositional heterogeneity of the Kaapvaal peridotite xenoliths results in up to 3 % variation in density and in up to 2.3 % variation of V p , V s , and V p /V s ratio. Fe depletion by melt extraction increases V p and V s , but decreases the V p /V s ratio and density. Orthopyroxene enrichment due to metasomatism decreases the density and V p , strongly reducing the V p /V s ratio. Garnet enrichment, which was also attributed to metasomatism, increases the density, and in a lesser extent V p and the V p /V s ratio. Comparison of density and seismic velocity profiles calculated using the xenoliths' compositions and equilibration conditions to seismological data in the Kaapvaal highlights that (i) the thickness of the craton is underestimated in some seismic studies and reaches at least 180 km, (ii) the deep sheared peridotites represent very local modifications caused and oversampled by kimberlites, and (iii) seismological models probably underestimate the compositional heterogeneity in the Kaapvaal man...

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Stabilisation of Archaean lithospheric mantle: A ReOs isotope study of peridotite xenoliths from the Kaapvaal craton

Cited by 420 publications

References 50 publications

Formation and evolution of Archaean cratons: insights from southern Africa

Formation and evolution of Archaean cratons: insights from southern Africa

Understanding Deep Earth Dynamics:A Numerical Modelling Approach

Petrophysical constraints on the seismic properties of the Kaapvaal craton mantle root

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