Small-scale convection under the back-arc occurring in the low viscosity wedge

Honda, Sawao; Saito, M.

doi:10.1016/s0012-821x(03)00537-5

Cited by 104 publications

(91 citation statements)

References 23 publications

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“…Back-arc extension on an oceanic plate leads to remnant island arcs, and the elevated mantle temperatures will lead to more vigorous small convection that can easily aid in the removal of the CMTL layer in remnant arcs and active arcs. Numerical experiments have shown that small scale convection under continental back-arcs (Currie and Hyndman, 2006) and oceanic back-arcs (Honda and Saito, 2003) is necessary to fit heat flow measurements, low viscosity layers under back-arcs, and seismic anisotropy observations. Indeed, small scale convection under the Izu-Bonin Arc, as inferred by the spatial and temporal patterns of volcanic activity (Honda et al, 2007), would aid in removal of the CMTL layers under the Izu, Bonin, and Mariana, active island arcs and their remnant arcs.…”

Section: From Fat To Accreted Terranementioning

confidence: 99%

Future accreted terranes: a compilation of island arcs, oceanic plateaus, submarine ridges, seamounts, and continental fragments

Tetreault

Buiter

2014

Solid Earth

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Abstract. Allochthonous accreted terranes are exotic geologic units that originated from anomalous crustal regions on a subducting oceanic plate and were transferred to the overriding plate by accretionary processes during subduction. The geographical regions that eventually become accreted allochthonous terranes include island arcs, oceanic plateaus, submarine ridges, seamounts, continental fragments, and microcontinents. These future allochthonous terranes (FATs) contribute to continental crustal growth, subduction dynamics, and crustal recycling in the mantle. We present a review of modern FATs and their accreted counterparts based on available geological, seismic, and gravity studies and discuss their crustal structure, geological origin, and bulk crustal density. Island arcs have an average crustal thickness of 26 km, average bulk crustal density of 2.79 g cm −3 , and three distinct crustal units overlying a crust-mantle transition zone. Oceanic plateaus and submarine ridges have an average crustal thickness of 21 km and average bulk crustal density of 2.84 g cm −3 . Continental fragments presently on the ocean floor have an average crustal thickness of 25 km and bulk crustal density of 2.81 g cm −3 . Accreted allochthonous terranes can be compared to these crustal compilations to better understand which units of crust are accreted or subducted. In general, most accreted terranes are thin crustal units sheared off of FATs and added onto the accretionary prism, with thicknesses on the order of hundreds of meters to a few kilometers. However, many island arcs, oceanic plateaus, and submarine ridges were sheared off in the subduction interface and underplated onto the overlying continent. Other times we find evidence of terrane-continent collision leaving behind accreted terranes 25-40 km thick. We posit that rheologically weak crustal layers or shear zones that were formed when the FATs were produced can be activated as detachments during subduction, allowing parts of the FAT crust to accrete and others to subduct. In many modern FATs on the ocean floor, a sub-crustal layer of high seismic velocities, interpreted as ultramafic material, could serve as a detachment or delaminate during subduction.

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Section: From Fat To Accreted Terranementioning

confidence: 99%

Future accreted terranes: a compilation of island arcs, oceanic plateaus, submarine ridges, seamounts, and continental fragments

Tetreault

Buiter

2014

Solid Earth

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“…Because the low-V and high-PR zones are generally considered to reflect the magma-related hot and wet anomalies caused by slab dehydration and corner flow in the mantle wedge, the along-arc variations of the low-V and high-PR zones indicate a spatial variation in the amount of fluids released from the slab dehydration, as well as in the strength of mantle-wedge corner flow along the arc. It was proposed that the along-arc variation of the velocity anomalies under NE Japan is due to small-scale convection occurring in the mantle wedge, similar to that under the cooling oceanic lithosphere (Honda et al, 2002;Honda and Saito, 2003). Such a small-scale convection can take place because the viscosity in the mantle wedge can be reduced significantly by the water released from the subducting slab.…”

Section: Slab Dehydration and Mantle Wedge Convectionmentioning

confidence: 99%

Tomography and Dynamics of Western-Pacific Subduction Zones

Zhao¹

2012

Monogr. Environ. Earth Planets

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We review the significant recent results of multiscale seismic tomography of the Western-Pacific subduction zones and discuss their implications for seismotectonics, magmatism, and subduction dynamics, with an emphasis on the Japan Islands. Many important new findings are obtained due to technical advances in tomography, such as the handling of complex-shaped velocity discontinuities, the use of various later phases, the joint inversion of local and teleseismic data, tomographic imaging outside a seismic network, and P-wave anisotropy tomography. Prominent low-velocity (low-V ) and high-attenuation (low-Q) zones are revealed in the crust and uppermost mantle beneath active arc and back-arc volcanoes and they extend to the deeper portion of the mantle wedge, indicating that the low-V /low-Q zones form the sources of arc magmatism and volcanism, and the arc magmatic system is related to deep processes such as convective circulation in the mantle wedge and dehydration reactions in the subducting slab. Seismic anisotropy seems to exist in all portions of the Northeast Japan subduction zone, including the upper and lower crust, the mantle wedge and the subducting Pacific slab. Multilayer anisotropies with different orientations may have caused the apparently weak shear-wave splitting observed so far, whereas recent results show a greater effect of crustal anisotropy than previously thought. Deep subduction of the Philippine Sea slab and deep dehydration of the Pacific slab are revealed beneath Southwest Japan. Significant structural heterogeneities are imaged in the source areas of large earthquakes in the crust, subducting slab and interplate megathrust zone, which may reflect fluids and/or magma originating from slab dehydration that affected the rupture nucleation of large earthquakes. These results suggest that large earthquakes do not strike anywhere, but in only anomalous areas that may be detected with geophysical methods. The occurrence of deep earthquakes under the Japan Sea and the East Asia margin may be related to a metastable olivine wedge in the subducting Pacific slab. The Pacific slab becomes stagnant in the mantle transition zone under East Asia, and a big mantle wedge (BMW) has formed above the stagnant slab. Convective circulations and fluid and magmatic processes in the BMW may have caused intraplate volcanism (e.g., Changbai and Wudalianchi), reactivation of the North China craton, large earthquakes, and other active tectonics in East Asia. Deep subduction and dehydration of continental plates (such as the Eurasian plate, Indian plate and Burma microplate) are also found, which have caused intraplate magmatism (e.g., Tengchong) and geothermal anomalies above the subducted continental plates. Under Kamchatka, the subducting Pacific slab shortens toward the north and terminates near the Aleutian-Kamchatka junction. The slab loss was induced by friction with the surrounding asthenosphere, as the Pacific plate rotated clockwise 30 Ma ago, and then it was enlarged by the slab-edge pinch-off b...

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“…9.13). On the contrary, the weakness of the mantle wedge might induce detachment of the subduction channels by convection (Honda et al 2002(Honda et al , 2007Honda and Saito 2003) and/or thermal-chemical plumes (Tamura 1994;Hall and Kincaid 2001;Gerya and Yuen 2003;Obata and Takazawa 2004;Manea et al 2005;Gorczyk et al 2007) in the mantle wedge. This problem should be clarified more quantitatively in the future by using 2-D or 3-D numerical studies.…”

Section: Total Volume Of Subducted Continental Materialsmentioning

confidence: 99%

Effect of Water on Subduction of Continental Materials to the Deep Earth

Ichikawa

Kawai

Yamamoto

et al. 2015

The Earth's Heterogeneous Mantle

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The flows in the subduction channels with wet mantle wedge are calculated by 1-D finite difference method with fine numerical resolutions. The water content largely affects the viscosity of the mantle wedge. Previous simulation result using dry rheology on the mantle wedge shows that viscosity of the subduction channels controls the process and that the sustainable thickness of the channel in the deep mantle is ~2-3 km. However, little is known about the effect of the water content in the mantle wedge on the subduction channels. Here, in order to estimate the supply rate of continental materials to the deep mantle with water-rich environment on the mantle wedge, we have conducted a numerical simulation of a subduction channel. The results show that the water content controls the flux of the continental materials especially when temperature of mantle wedge is high. Therefore, the water content of the mantle wedge can be more important in the ancient mantle because of its high temperature.

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Small-scale convection under the back-arc occurring in the low viscosity wedge

Cited by 104 publications

References 23 publications

Future accreted terranes: a compilation of island arcs, oceanic plateaus, submarine ridges, seamounts, and continental fragments

Future accreted terranes: a compilation of island arcs, oceanic plateaus, submarine ridges, seamounts, and continental fragments

Tomography and Dynamics of Western-Pacific Subduction Zones

Effect of Water on Subduction of Continental Materials to the Deep Earth

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