Effects of variable thermal conductivity on the mineralogy of subducting slabs and implications for mechanisms of deep earthquakes

Marton, F. C.; Shankland, T. J.; Rubie, D. C.; Xu, Yongfu

doi:10.1016/j.pepi.2004.08.026

Cited by 39 publications

(28 citation statements)

References 40 publications

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“…For mantle rocks, one must account for scattering and for the effect of interfaces in a mineral assemblage. Such complications led Marton et al [2005] to use a constant radiative conductivity component k r = 1 W m −1 K −1 for temperatures larger than 700 K. Gibert et al [2005], however, have found that the conductivity of polycrystalline dunite samples conforms to relation (B3) and is close to that of single olivine crystals. For 700 < T < 1700 K, which is the range of interest for thick lithospheric roots, equation (B3) leads to 0.13 < k r < 1.8 W m −1 K −1 which is close to the approximation of a constant k r at a value of 1 W m −1 K −1 .…”

Section: Appendix B: Thermal Conductivitymentioning

confidence: 99%

Low heat flux and large variations of lithospheric thickness in the Canadian Shield

Lévy¹,

Jaupart²,

Mareschal³

et al. 2010

J. Geophys. Res.

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[1] Ten new heat flux determinations have been made using measurements in 22 mining exploration boreholes located at latitudes higher than 51°N in the Canadian Shield. They provide data in poorly sampled regions near the core of the North American craton where one expects the lithosphere to be thickest. The new heat flux values are all smaller than 34 mW m −2 and are among the lowest recorded so far in the shield. For all the new sites, there is no relationship between heat flux and heat production in surface rocks. In the Canadian Shield, heat flux variations occur at wavelengths <100 km and are mostly of crustal origin. Local averages in two 250 × 250 km windows located on Archean areas at high latitudes on either side of James Bay are 29 mW m −2 and 31 mW m −2 , the lowest values found so far at this scale in the Canadian Shield. S wave traveltime delays derived from tomographic models provide the additional constraints needed to resolve differences of deep lithospheric thermal structure. There is no significant correlation between average surface heat flux and traveltime delays within the Canadian Shield, confirming that variations of the surface heat flux are mostly of crustal origin. Traveltime delays cannot be explained by variations in crustal heat production only and require variations of heat supply to the lithosphere and/or radiogenic heat production in the lithospheric mantle. These variations are associated with changes of lithospheric thickness that may be as large as 80 km. The heat flux at the base of the Superior lithosphere is constrained to be 11 ± 2 mW m −2 .

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Section: Appendix B: Thermal Conductivitymentioning

confidence: 99%

Low heat flux and large variations of lithospheric thickness in the Canadian Shield

Lévy¹,

Jaupart²,

Mareschal³

et al. 2010

J. Geophys. Res.

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“…Figure 6 shows the thermal diffusivity of MORB composition majorite and eclogite, along with the polymorphs of Mg 2 SiO 4 (from Xu et al, 2004), plotted as a function of temperature. The thermal diffusivities of the MORB assemblages measured here are similar to that of olivine and 30-40% smaller than that of wadsleyite and ringwoodite at 1000 K. Thermal models of subducting slabs which use the thermal conductivities of the appropriate mineral assemblage (Marton et al, 2005) show that the extent of metastable olivine is reduced compared to earlier thermal models which just used olivine thermal conductivities. The present results, which show that the thermal diffusivity (and hence thermal conductivity) of majorite is similar to that of olivine would suggest that the MORB layer on the top of the subducting slab would have an anomalously low thermal conductivity, compared to the surrounding wadsleyite-and ringwoodite-rich assemblages, in the transition zone.…”

Section: Discussionmentioning

confidence: 46%

Thermal diffusivity of MORB-composition rocks to 15 GPa: implications for triggering of deep seismicity

Dobson

Hunt

McCormack

et al. 2010

High Pressure Research

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“…Thermal conductivity (k) is obviously an influential parameter and is fixed at 3.138 J·m −1 K −1 s −1 in our simulations (Marton et al 2005). As k may decrease with temperature (Emmerson and McKenzie 2007), we investigate a range of k from 2.9 to 3.2 J · m −1 K −1 s −1 .…”

Section: Location Of the Former Oceanic Moho Relative To The Deep Earmentioning

confidence: 99%

Dominant role of temperature on deep earthquake mechanics for the Tonga slab near the bottom of the upper mantle

Kaneshima

Yoshioka

2014

Earth Planet Sp

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The effects of temperature on the mechanics of deep earthquakes are investigated based on detailed seismic images of a horizontal portion of the Tonga slab (19°S to 22°S). The hypocenter distribution of deep earthquakes and tomographic models have shown that the Tonga slab in this region stagnates laterally around the upper-and lower-mantle boundary. We analyze data from seismic networks in the United States and Japan from the deepest earthquakes that occurred in the stagnating part of the slab (focal depths 658 to 678 km). We observe a clear arrival approximately 8 s after the direct P wave and find that it is an S-to-P converted wave emitted upward from the deepest earthquake foci and reflected downward by a horizontal interface located nearly 30 km above the foci. The S wave speed drops upward across the interface by a few percent, so the interface is best interpreted as the former oceanic Moho in the stagnating Tonga slab. A numerical model of the thermal structure of the Tonga slab is constructed based upon the slab geometry, with the dynamics of the slab motion being incorporated. We find that if the deepest earthquakes occur in the coldest part of the slab, the vertical distance between the foci and the Moho should be approximately 30 km, which agrees well with the observations. The temperature around the foci is determined to be 750°C. We suggest that deep earthquakes are stringently restricted below this temperature, near the bottom of the upper mantle.

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Effects of variable thermal conductivity on the mineralogy of subducting slabs and implications for mechanisms of deep earthquakes

Cited by 39 publications

References 40 publications

Low heat flux and large variations of lithospheric thickness in the Canadian Shield

Low heat flux and large variations of lithospheric thickness in the Canadian Shield

Thermal diffusivity of MORB-composition rocks to 15 GPa: implications for triggering of deep seismicity

Dominant role of temperature on deep earthquake mechanics for the Tonga slab near the bottom of the upper mantle

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