Early formation and long-term stability of continents resulting from decompression melting in a convecting mantle

Smet, Jan De; Berg, A. P. van den; Vlaar, N. J.

doi:10.1016/s0040-1951(00)00055-x

Cited by 26 publications

(18 citation statements)

References 30 publications

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“…This may explain the longevity of the Archean craton, by preventing the lithosphere from sinking into the asthenosphere. This hypothesis was formulated quite early [ Jordan , 1979], but strong observational or numerical evidence is recent [ Forte and Perry , 2000; de Smet et al , 2000; Deschamps et al , 2002]. …”

Section: Discussionmentioning

confidence: 99%

Thermal and compositional anomalies beneath the North American continent

et al. 2004

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[1] The thermal and compositional structure of the upper mantle beneath the North American continent is investigated using a joint inversion of seismic velocities and density perturbations. The velocity data consist of a new regional shear wave velocity model of North America and the Caribbean region obtained by surface wave tomography. The density data are estimated using a relative density-to-shear velocity scaling factor computed for continents by combining regionally filtered seismic and gravity data. We express the mineralogical variations in the mantle in terms of the global volumic fraction of iron, the parameter which has the strongest influence on density and velocity. The inferred thermal and iron content anomalies are well constrained by the data and show an age dependence down to a depth of 230 ± 50 km. Below the North American craton, the mantle is colder than average and depleted in iron. Maximum values are found at 100 km with dT = À440 K and dFe = À4%, relative to the average mantle. These chemical and thermal characteristics induce opposite buoyancy forces which could explain the longevity of cratonic lithosphere. In stable continental areas, the signal is of lower amplitudes (dT = À280 K and dFe = À2.5% at 100 km). Beneath the western Cordillera, a tectonically active region, we see no significant thermal or chemical anomaly.

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Section: Discussionmentioning

confidence: 99%

Thermal and compositional anomalies beneath the North American continent

et al. 2004

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“…The presence of an early magma ocean is important in our discussion because (1) it provides bounds on the thermal regime at the time the magma ocean freezes and (2) it provides estimates of the initial differentiation, and therefore the mantle composition, of the very young Earth (Abe, 1997). Early massive differentiation is suggested by Hf isotope data that suggest a depleted mantle that is at least 4.08 Ga (Amelin et al, 2000;van Thienen et al, 2004a) or even older, 4.4-4.5 Ga (Harrison et al, 2005), although other mechanisms have been proposed (de Smet et al, 2000;Davies, 2006).…”

Section: Magma Oceanmentioning

confidence: 99%

Tectonics of early Earth: Some geodynamic considerations

Hunen

Keken²,

Hynes³

et al. 2008

Special Paper 440: When Did Plate Tectonics Begin on Planet Earth?

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Today, plate tectonics is the dominant tectonic style on Earth, but in a hotter Earth tectonics may have looked different due to the presence of more melting and associated compositional buoyancy as well as the presence of a weaker mantle and lithosphere. Here we review the geodynamic constraints on plate tectonics and proposed alternatives throughout Earth's history. Observations suggest a 100-300 °C mantle potential temperature decrease since the Archean. The use of this range by theoretical studies, parameterized convection studies, and numerical simulations puts a number of constraints on the viability of the different tectonic styles. The ability to suffi ciently cool early Earth with its high radiogenic heat production forms one of the major constraints on the success of any type of tectonics. The viability of plate tectonics is mainly limited by the availability of suffi cient driving forces and lithospheric strength. Proposed alternative mechanisms include local or global magma oceans, diapirism, independent dynamics of crust and underlying mantle, and large-scale mantle overturns. Transformation of basaltic crust into dense eclogite is an important driving mechanism, regardless of the governing tectonic style.

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“…If a no-flow boundary condition were used instead, all the initial chemical lithosphere remains trapped in the box of the model. In that case, entrained chemical lithosphere is swept back to the surface in upwellings as in the models of De Smet et al [2000].…”

Section: Spatial Boundary Conditions For Numerical Modelsmentioning

confidence: 99%

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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Early formation and long-term stability of continents resulting from decompression melting in a convecting mantle

Cited by 26 publications

References 30 publications

Thermal and compositional anomalies beneath the North American continent

Thermal and compositional anomalies beneath the North American continent

Tectonics of early Earth: Some geodynamic considerations

Survival of Archean cratonal lithosphere

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