Constraints on the abundance of eclogite in the upper mantle

Schulze, Daniel J.

doi:10.1029/jb094ib04p04205

Cited by 151 publications

(78 citation statements)

References 29 publications

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“…This finding strengthens the possibility that the cratonic lithosphere formed initially in subduction-zone settings whose demise led to accretion of the arc crust and thickening of refractory mantle to create a stable, thick, continental lithosphere (Carlson et al 2000;Grove et al 2000). The paucity of eclogite xenoliths (<1% (Schulze 1989) indicates that essentially all of the descending oceanic plates during Archaean time were subducted into the deeper mantle, with little eclogitic material incorporated into the cratonic root.…”

Section: Primary Results From Geochemistry and Petrologymentioning

confidence: 99%

“…Jordan showed, for example, that fertile cratonic samples contain significant weight percentages of both clinopyroxene and garnet, resulting in seismic velocities up to 1% lower and densities 1-2% higher than the depleted nodular peridotites (Jordan 1979). Similarly, eclogitic mantle, if present (Shirey et al 2001), will have both lower velocity and higher density than depleted peridotitic mantle at the same temperature, although an inventory of mantle xenoliths of the Kaapvaal Craton suggests that the cratonic mantle is <1% eclogite by volume (Schulze 1989).…”

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: Primary Results From Geochemistry and Petrologymentioning

confidence: 99%

Section: Tectospheric Rootsmentioning

confidence: 99%

Formation and evolution of Archaean cratons: insights from southern Africa

James

Fouch

2002

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“…Smith (1982) assumed that the heat pulse needed to drive this change was supplied to the base of the African lithosphere in the Mesozoic as it passed across the slightly hotter asthenosphere in a fixed plate tectonic reference framework, with uplift following about ~60 tõ 50 Ma, given a thermal time constant (thermal diffusivity) of about 60 million years. However, xenolith studies suggest that the eclogite volume in the southern African cratonic lithosphere is small (<1%; Schulze 1989) and because the phase transition upon heating near the Moho will be to garnet granulite rather than directly to basalt, this is apparently not a significant factor that could have controlled the marked uplift history of southern Africa. However, this could be a more important factor in the off-craton regions where there is evidence for mafic material in the upper mantle and lower crust (Durheim and Mooney, 1994;Carlson et al, 2006).…”

Section: Metasomatism In the Lithospheric Mantle Across Southern Africamentioning

confidence: 99%

The Kalahari Epeirogeny and climate change: differentiating cause and effect from core to space

Wit

2007

South African Journal of Geology

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Southern Africa's high Kalahari plateau and its flanking mountain ranges formed over an extended period of ~200 million years through vertical tectonic processes different from those at convergent plate boundaries. We refer to this as the Kalahari epeirogeny. Episodic uplift and erosion during the Kalahari epeirogeny is inferred from thermo-chronology and from stratigraphy of sediment accumulated around its continental margin. A total thickness of 2 to 7 km of rock (of which basalt was a major component) was eroded from the subcontinent's surface during two punctuated episodes of exhumation, in the early-Cretaceous and in the mid-Cretaceous. Major exhumation was over by the end of the Cretaceous, and the rate of erosion decreased by more than an order of magnitude to remove less than 1 km thickness of rock during the Cenozoic. Cosmogenic dating shows that erosion rates today are almost an order of magnitude less still.The cause for the Kalahari epeirogeny remains elusive, but three striking observations stand out: (i) major exhumation occurred during the late Mesozoic break-up of Gondwana; (ii) large scale basaltic magmatism closely match two accelerated episodes of exhumation: first along the west coast (~132 Ma, Etendeka large igneous province [LIP], associated with vast amounts of underplating along this entire passive margin), and the second flanking the sheared south coast margin (~90 Ma, Agulhas oceanic LIP). Yet exhumation that might have accompanied the vast Karoo LIP (~180 Ma) is not readily detected; (iii) the two main regional episodes of accelerated exhumation and coastal sediment accumulation are near synchronous with two regional 'spikes' of kimberlite intrusions: >450 kimberlites at ~90 Ma, and >200 kimberlites at ~120 Ma. Southern Africa is underlain by an anomalous warm region in the lowermost ~1500 km of the mantle that is linked to core to mantle heat loss. This warm region was inherited from a large Cretaceous thermo-chemical anomaly in the mantle created during long-lived subduction beneath Gondwana. Associated Mesozoic kimberlite genesis and basaltic magmatism may have been sufficient to cause volatile/heat-induced density changes in the lithospheric mantle of southern Africa to sustain the Kalahari plateau. In addition, such changes may have been induced by tectonic uplift and decompressional melting resulting from far-field collision processes between Africa and Europe, and/or final continental lithosphere decoupling between the Falkland plateau and southern Africa. CO 2 released into the ocean-atmosphere system during the Kalahari epeirogeny contributed to the global mid-Cretaceous hot-house conditions. However, because the CO 2 -consumption rate associated with basalt weathering is about eight times that of granite, atmospheric CO 2 was also efficiently sequestrated during the rapid erosion of Karoo basalt. Thus, the Kalahari epeirogeny also may have catalysed the onset of long-term global Cenozoic cooling.

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“…In the second model, imbrication of buoyant oceanic lithosphere during lateral tectonic accretion is responsible for forming SCLM [e.g., Helmstaedt and Schulze, 1989]. However, such a lateral tectonic accretion model implies a greater amount of eclogite in SCLM than is implied by mantle-derived xenoliths [Schulze, 1989]. A third, though less popular, model envisages SCLM as a result of continental collision [e.g., Jordan, 1978].…”

Section: Introductionmentioning

confidence: 99%

Geodynamic models of Archean continental collision and the formation of mantle lithosphere keels

Gray

Pysklywec

2010

Geophysical Research Letters

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The processes responsible for the formation of thick, strong and cold Archean sub‐continental lithospheric mantle (mantle keels) beneath Archean cratons remain elusive. Here, the dynamics of some such processes are studied by forward numerical modeling of the thermo‐mechanical evolution of continental lithosphere undergoing collision and orogenesis under Neoarchean‐like conditions. The numerical experiments illustrate that depending on the composition of the crust and the degree of radioactive heat production (RHP) in the crust, three dominant modes of mantle lithosphere deformation evolve: (1) pure‐shear thickening; (2) imbrication; (3) and a mode best described as underplating. All three modes of deformation result in the thickening and emplacement of plate‐like mantle lithosphere to depths between 200 km and 350 km. The transition from pure‐shear thickening to imbrication is largely dependent on the degree of RHP in the crust, while the transition from the imbrication style to the underplating style is dependent on the composition of the lower crust.

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Constraints on the abundance of eclogite in the upper mantle

Cited by 151 publications

References 29 publications

Formation and evolution of Archaean cratons: insights from southern Africa

Formation and evolution of Archaean cratons: insights from southern Africa

The Kalahari Epeirogeny and climate change: differentiating cause and effect from core to space

Geodynamic models of Archean continental collision and the formation of mantle lithosphere keels

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