Grain-size evolution in subducted oceanic lithosphere associated with the olivine-spinel transformation and its effects on rheology

Riedel, Michael R.; Karato, Shun‐ichiro

doi:10.1016/s0012-821x(97)00016-2

Cited by 142 publications

(77 citation statements)

References 35 publications

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“…Any slab weakening mechanism, such as grain-size reduction accompanying a phase change [Rubie, 1984;Riedel and Karato, 1997] or warming of the slab due to latent heat effects [van Hunen et al, 2001] would lead to steeper slabs that sink directly into the lower mantle, if there is no lateral migration in the upper mantle, similar to our models with a lower yield stress.…”

Section: Other Factors Affecting Slab Dynamicssupporting

confidence: 63%

Rheologic controls on slab dynamics

Billen

Hirth

2007

Geochem Geophys Geosyst

201

186

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[1] Several models have been proposed to relate slab geometry to parameters such as plate velocity or plate age. However, studies on the observed relationships between slab geometry and a wide range of subduction parameters show that there is not a simple global relationship between slab geometry and any one of these other subduction parameters for all subduction zones. Numerical and laboratory models of subduction provide a method to explore the relative importance of different physical processes in determining subduction dynamics. Employing 2-D numerical models with a viscosity structure constrained by laboratory experiments for the deformation of olivine, we show that the observed range in slab dip and the observed trends between slab dip and convergence velocity, subducting plate age, and subduction duration can be reproduced without trench motion (i.e., slab roll-back) for locations away from slab edges. Successful models include a stiff slab that is 100-1000 times more viscous than previous estimates from models of plate bending, the geoid, and global plate motions. We find that slab dip in the upper mantle depends primarily on slab strength and plate boundary coupling, with a small dependence on subducting plate age. Once the slab sinks into the lower mantle the primary processes controlling slab evolution are (1) the ability of the stiff slab to transmit stresses up dip, (2) resistance to slab descent into the higherviscosity lower mantle, and (3) subduction-induced flow in the mantle-wedge corner.

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Section: Other Factors Affecting Slab Dynamicssupporting

confidence: 63%

Rheologic controls on slab dynamics

Billen

Hirth

2007

Geochem Geophys Geosyst

201

186

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“…Riedel and Karato [1997] calculated that the grain size of spinel could be reduced to about 0.1 mm when the olivine -spinel transformation occurs at relatively low temperature. Figure 3 shows that spinel with a grain size less than about 1 mm can become weaker than the surrounding mantle.…”

Section: Discussionmentioning

confidence: 99%

Silicon self‐diffusion in wadsleyite: Implications for rheology of the mantle transition zone and subducting plates

Shimojuku

Kubo

Ohtani

et al. 2004

Geophysical Research Letters

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[1] Si self-diffusion rates in Mg 2 SiO 4 polycrystalline wadsleyite were measured at 18 GPa and 1430 -1630°C using an isotopic tracer ( 29 Si) and secondary ion mass spectrometry. The volume diffusion coefficient (D v ) and grain-boundary diffusion coefficient (D gb ) were determined to be D v = 3.44 Â 10 À11 [m 2 /s] exp (À299 [kJ/mol]/RT) and dD gb = 1.14 Â 10 À17 [m 3 /s] exp (À248 [kJ/mol]/RT), respectively. Si diffusion rates in wadsleyite are about 5 orders of magnitude slower than Mg-Fe interdiffusion rates at 1400°C. Assuming that Si is the slowest diffusing species in wadsleyite, the geophysical model of the viscosity in the mantle transition zone can be explained by diffusion creep in wadsleyite for a grain size of about 0.5-5 mm. Some portions in cold subducting slabs, where the grain size reduces to less than 1 mm after the olivinespinel transformation, become weaker than the surrounding mantle.

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“…It determines the buoyancy force applied to the slab, which could drive or oppose subduction [Schubert et al, 1975;Sung et al, 1976]. It also determines the rheology [Riedel and Karato, 1997] …”

mentioning

confidence: 99%

Formation of a metastable olivine wedge in a descending slab

Dévaux¹,

Schubert²,

Anderson³

1997

J. Geophys. Res.

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Abstract.We present a thermal model of a descending slab in which the transformation of olivine to spinel is controlled by pressure-and temperature-dependent reaction kinetics. Two different formulations of the kinetics are considered with the main discriminant being the temperature range over which olivine converts to spinel at pressures of about 15 GPa (about 500ø-515øC and 560ø-650øC). We use a finite element method to solve the coupled heat conduction (perpendicular and parallel to the dip of the slab) and kinetics equations, and we include the latent heat of the phase transformation. Latent heat release together with heat conduction parallel to the dip of the slab reduces significantly the length of the metastable olivine wedge and results in a very thin ( •< 5 km) two-phase region. We employ the thermal parameter vr sin 5 (v is the velocity of the descending slab, r is the age of the slab, and 5 is the dip of the slab to the horizontal) to interpret the results for the length of the metastable wedge. For values of the thermal parameter smaller than about 4000 and 7000 km, depending on the model of the kinetics, no metastable olivine wedge exists (the critical value of 7000 km for the thermal parameter corresponds to the kinetics model with the lowest transition temperature range). The length of the metastable olivine wedge is also found to be very sensitive to the model of the kinetics and to the effects of adiabatic heating. If the occurrence of deep earthquakes is related to the transformation of metastable olivine to spinel, then data on earthquake depth versus thermal parameter require that the onset of the reaction takes place at temperatures of about 550ø-575øC. In this case the slab thermal parameter must be larger than 10,000 km for the metastable olivine wedge to extend down to 660 km depth. But deep earthquakes occur near 660 km depth in slabs with thermal parameter as small as about 5000 km (South America, for example). Either some deep earthquakes are unrelated to olivine metastability or our knowledge of olivine-spinel reaction kinetics is incomplete.

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Grain-size evolution in subducted oceanic lithosphere associated with the olivine-spinel transformation and its effects on rheology

Cited by 142 publications

References 35 publications

Rheologic controls on slab dynamics

Rheologic controls on slab dynamics

Silicon self‐diffusion in wadsleyite: Implications for rheology of the mantle transition zone and subducting plates

Formation of a metastable olivine wedge in a descending slab

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