Onset of small-scale instabilities at the base of the lithosphere: scaling laws and role of pre-existing lithospheric structures

Dumoulin, Caroline; Doin, Marie‐Pierre; Arcay, Diane; Fleitout, Luce

doi:10.1111/j.1365-246x.2004.02475.x

Cited by 30 publications

(55 citation statements)

References 27 publications

(81 reference statements)

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“…It has been shown that the effective viscosity at the lithosphere base, corresponding to a minimum if T -and P -dependences are both modelled, is crucial in triggering of small-scale convective processes (e.g. Davaille and Jaupart, 1993;Dumoulin et al, 2001;Morency et al, 2002;Dumoulin et al, 2005), as well as in subduction initiation, as it favours, if low enough, the corner flow activation necessary to stop the kinematic decoupling and mechanical coupling between the two converging plates at high depths (e.g. Doin…”

Section: Choice Of Rheological Parameter Setsmentioning

confidence: 99%

Dynamics of interplate domain in subduction zones: influence of rheological parameters and subducting plate age

Arcay

2012

Solid Earth

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Abstract. The properties of the subduction interplate domain are likely to affect not only the seismogenic potential of the subduction area but also the overall subduction process, as it influences its viability. Numerical simulations are performed to model the long-term equilibrium state of the subduction interplate when the diving lithosphere interacts with both the overriding plate and the surrounding convective mantle. The thermomechanical model combines a nonNewtonian viscous rheology and a pseudo-brittle rheology. Rock strength here depends on depth, temperature and stress, for both oceanic crust and mantle rocks. I study the evolution through time of, on one hand, the brittle-ductile transition (BDT) depth, z BDT , and, on the other hand, of the kinematic decoupling depth, z dec , simulated along the subduction interplate. The results show that both a high friction and a low ductile strength at the asthenospheric wedge tip shallow z BDT . The influence of the weak material activation energy is of second order but not negligible. z BDT becomes dependent on the ductile strength increase with depth (activation volume) if the BDT occurs at the interplate decoupling depth. Regarding the interplate decoupling depth, it is shallowed (1) significantly if mantle viscosity at asthenospheric wedge tip is low, (2) if the difference in mantle and interplate activation energy is weak, and (3) if the activation volume is increased. Very low friction coefficients and/or low asthenospheric viscosities promote z BDT = z dec . I then present how the subducting lithosphere age affects the brittle-ductile transition depth and the kinematic decoupling depth in this model. Simulations show that a rheological model in which the respective activation energies of mantle and interplate material are too close hinders the mechanical decoupling at the down-dip extent of the interplate, and eventually jams the subduction process during incipient subduction of a young (20-Myr-old) and soft lithosphere under a thick upper plate. Finally, both the BDT depth and the decoupling depth are a function of the subducting plate age, but are not influenced in the same fashion: cool and old subducting plates deepen the BDT but shallow the interplate decoupling depth. Even if BDT and kinematic decoupling are intrinsically related to different mechanisms of deformation, this work shows that they are able to interact closely. Comparison between modelling results and observations suggests a minimum friction coefficient of 0.045 for the interplate plane, even 0.069 in some cases, to model realistic BDT depths. The modelled z dec is a bit deeper than suggested by geophysical observations. Eventually, the better way to improve the adjustment to observations may rely on a moderate to strong asthenosphere viscosity reduction in the metasomatised mantle wedge.

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Section: Choice Of Rheological Parameter Setsmentioning

confidence: 99%

Dynamics of interplate domain in subduction zones: influence of rheological parameters and subducting plate age

Arcay

2012

Solid Earth

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“…Initially convection is weak and the conductive geotherm in (6) is a good approximation of the actual geotherm. The thickness of the rheological boundary layer is proportional to the lithosphere thickness, which increases with the square root of age [64].…”

Section: Transient Heat Flow Through Oceanic Lithospherementioning

confidence: 99%

“…Sleep [17] gave calibrated relationships based on (17) for this situation. For comparison, Dumoulin et al [64,66] consider the time of convection to become vigorous which is analogous to t s using Rayeligh numbers. Their work utilizes t s , but their equations cannot be manipulated into the forms of (34) and (35).…”

Section: The Transient Heat Flow Equation (17) Then Becomes In Normalmentioning

confidence: 99%

“…The lithospheric relief associated with fracture zones modulates the planform of convection [52,64,66]. Closely spaced hotspot lines of volcanic edifices may indicate underlying smallscale convection in somewhat hotter regions of the mantle [32,33].…”

Section: Further Work On Three-dimensional Dynamical Featuresmentioning

confidence: 99%

“…In the presence of conduction only, the deep boundary between thick old lithosphere and thin young lithosphere directly underlies the surface trace of ridge-ridge fracture zones. The escarpment on the base of the lithosphere modulates small-scale convection so that downwelling occurs on the old side and the boundary between thick and thin lithosphere migrates toward the old side as the plate ages [52,64,66]. Lithospheric relief associated with the base of the fracture zone disappears as steady state is approached [66].…”

Section: Fracture-zone Modulated Convectionmentioning

confidence: 99%

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Small-scale convection beneath oceans and continents

Sleep

2011

Chin. Sci. Bull.

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Small-scale convection supplies heat flow of ~17 mW m 2 to the base of stable continents where xenolith studies resolve the geotherm. However, effects of small-scale convection are difficult to resolve in ocean basins. On first pass, most seafloor appears to subside to an asymptote compatible with ~40 mW m 2 convective heat flow. These common regions are tracked by hotspots so uplift associated with ponded mantle material is an attractive alternative. Unaffected seafloor in the North and South Atlantic continues to subside with the square root of age as expected from pure conduction. The theory of stagnant-lid convection provides good scaling relationships for heat flow. For linear viscosity, heat flow is proportional to the underlying "half-space" viscosity to the 1/3 power and the temperature to change viscosity by a factor of e to the 4/3 power. The formalism is easily modified to represent convection beneath a lid of highly viscous and buoyant cratonal lithosphere and to represent transient convection beneath thickening oceanic lithosphere. Asthenospheric mantle with linear, strongly temperature-dependent, and weakly depth-dependent viscosity is compatible with both oceanic and continental data. More complicated rheology may allow vigorous small-scale convection under most but not all old ocean basins. Still viable hypotheses require poorly understood global features, including lateral variations of asthenospheric temperature. Seismological studies have the potential to resolve the lithosphere-asthenosphere boundary, including local variations of its depth associated with small-scale convection.lithosphere, asthenosphere, ocean depth-age, small-scale convection, craton, mantle plume Citation:Sleep N H. Small-scale convection beneath oceans and continents.

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Thermal evolution of the North Atlantic lithosphere: New constraints from magnetic anomaly inversion with a fractal magnetization model

Wang

Lin

et al. 2013

Geochem Geophys Geosyst

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[1] Using recently published global magnetic models, we present the first independent constraint on North Atlantic geothermal state and mantle dynamics from magnetic anomaly inversion with a fractal magnetization model. Two theoretical models of radial amplitude spectrum of magnetic anomalies are found almost identical, and both are applicable to detecting Curie depths in using the centroid method based on spectral linearization at certain wave number bands. Theoretical and numerical studies confirm the robustness of this inversion scheme. A fractal exponent of 3.0 in the magnetic susceptibility is found suitable, and Curie depths are well constrained by their known depths near the mid-Atlantic ridge. While generally increasing with growing ages, North Atlantic Curie depths show large oscillating and heterogeneous patterns related most likely to small-scale sublithospheric convections, which are found to have an onset time around 40 Ma and a scale of about 500 km, and are in preferred transverse rolls. Hotspots in North Atlantic also contribute to large geothermal and Curie-depth variations, but they appear to connect more closely to geochemical anomalies or small-scale convection than to mantle plumes. Curie depths can be correlated to heat flow gridded in a constant 1 interval, which reveals decreasing effective thermal conductivity with depths within the magnetic layer. North Atlantic Curie points are mostly beneath the Moho, suggesting that the uppermost mantle is magnetized from serpentinization and induces long-wavelength magnetic anomalies. Small-scale convection and serpentinization together may cause apparent flattening and deviations in heat flow and bathymetry from theoretical cooling models in old oceanic lithosphere.

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Onset of small-scale instabilities at the base of the lithosphere: scaling laws and role of pre-existing lithospheric structures

Cited by 30 publications

References 27 publications

Dynamics of interplate domain in subduction zones: influence of rheological parameters and subducting plate age

Dynamics of interplate domain in subduction zones: influence of rheological parameters and subducting plate age

Small-scale convection beneath oceans and continents

Thermal evolution of the North Atlantic lithosphere: New constraints from magnetic anomaly inversion with a fractal magnetization model

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