Slab

About: Slab is a research topic. Over the lifetime, 31617 publications have been published within this topic receiving 318693 citations.

Rheologic controls on slab dynamics

Abstract: 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 higher-viscosity lower mantle, and (3) subduction-induced flow in the mantle-wedge corner.

Viscosity jump in Earth’s mid-mantle

Abstract: The viscosity structure of Earth's deep mantle affects the thermal evolution of Earth, the ascent of mantle plumes, settling of subducted oceanic lithosphere, and the mixing of compositional heterogeneities in the mantle. Based on a reanalysis of the long-wavelength nonhydrostatic geoid, we infer viscous layering of the mantle using a method that allows us to avoid a priori assumptions about its variation with depth. We detect an increase in viscosity at 800- to 1200-kilometers depth, far greater than the depth of the mineral phase transformations that define the mantle transition zone. The viscosity increase is coincident in depth with regions where seismic tomography has imaged slab stagnation, plume deflection, and changes in large-scale structure and offers a simple explanation of these phenomena.

Subduction-transition zone interaction: A review

Abstract: As subducting plates reach the base of the upper mantle, some appear to flatten and stagnate, while others seemingly go through unimpeded. This variable resistance to slab sinking has been proposed to affect long-term thermal and chemical mantle circulation. A review of observational constraints and dynamic models highlights that neither the increase in viscosity between upper and lower mantle (likely by a factor 20–50) nor the coincident endothermic phase transition in the main mantle silicates (with a likely Clapeyron slope of –1 to –2 MPa/K) suffice to stagnate slabs. However, together the two provide enough resistance to temporarily stagnate subducting plates, if they subduct accompanied by significant trench retreat. Older, stronger plates are more capable of inducing trench retreat, explaining why backarc spreading and flat slabs tend to be associated with old-plate subduction. Slab viscosities that are ∼2 orders of magnitude higher than background mantle (effective yield stresses of 100–300 MPa) lead to similar styles of deformation as those revealed by seismic tomography and slab earthquakes. None of the current transition-zone slabs seem to have stagnated there more than 60 m.y. Since modeled slab destabilization takes more than 100 m.y., lower-mantle entry is apparently usually triggered (e.g., by changes in plate buoyancy). Many of the complex morphologies of lower-mantle slabs can be the result of sinking and subsequent deformation of originally stagnated slabs, which can retain flat morphologies in the top of the lower mantle, fold as they sink deeper, and eventually form bulky shapes in the deep mantle.

Seismic evidence for catastrophic slab loss beneath Kamchatka

Abstract: In the northwest Pacific Ocean, a sharp corner in the boundary between the Pacific plate and the North American plate joins a subduction zone running along the southern half of the Kamchatka peninsula1 with a region of transcurrent motion along the western Aleutian arc1,2. Here we present images of the seismic structure beneath the Aleutian–Kamchatka junction and the surrounding region, indicating that: the subducting Pacific lithosphere terminates at the Aleutian–Kamchatka junction; no relict slab underlies the extinct northern Kamchatka volcanic arc; and the upper mantle beneath northern Kamchatka has unusually slow shear wavespeeds. From the tectonic and volcanic evolution of Kamchatka over the past 10 Myr (refs 3, 4–5) we infer that at least two episodes of catastrophic slab loss have occurred. About 5 to 10 Myr ago, catastrophic slab loss shut down island-arc volcanic activity north of the Aleutian–Kamchatka junction. A later episode of slab loss, since about 2 Myr ago, seems to be related to the activity of the world's most productive island-arc volcano, Klyuchevskoy6. Removal of lithospheric mantle is commonly discussed in the context of a continental collision, but our findings imply that episodes of slab detachment and loss are also important agents in the evolution of oceanic convergent margins.