Slab

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

Melting features along the western Ryukyu slab edge (northeast Taiwan): Tomographic evidence

Abstract: [1] Behind the sedimentary Ryukyu arc lies the Okinawa Trough, whose termination is located at the tip of the Ilan plain (northern Taiwan), just above the Ryukyu slab edge. The present-day active volcanic front is located 80–100 km above the Ryukyu slab and extends from Japan to Kueishantao Island, an islet situated 10 km offshore the Ilan plain. Between December 1990 and May 1999, 3370 earthquakes recorded in northern Taiwan by 65 seismic land stations were used to determine the three-dimensional Vp and Vs velocity structures and Vp/Vs ratios. A low Vs but high Vp/Vs sausage-like body, ∼30 km in diameter, lies within the Eurasian mantle wedge, on top of the western Ryukyu slab extremity, at depths ranging between 20 and 100 km. We suggest that the H2O-rich component formed by dehydration processes from subducting sediments, oceanic crust, and serpentinized mantle above the Ryukyu slab and along the vertical portion of the slab edge might explain the presence of the sausage-like body. A low Vs but high Vp/Vs channel rises obliquely from the sausage-like body at a depth of 40 km in direction of the andesitic Kueishantao Island. We propose that the H2O-rich component and/or melt rise up from the sausage-like body and interfere with the Okinawa Trough back arc basin magmas formed in the upper mantle/lower crust. Then magmas propagate upward within the upper brittle crust through veins and/or narrow conduits.

Spreading pulses of the Tyrrhenian Sea during the narrowing of the Calabrian slab

Abstract: The opening of the Tyrrhenian Sea has been punctuated by short-lived episodes of oceanic accretion on separate small backarc basins during early Pliocene (Vavilov basin) and early Pleistocene (Marsili basin) time. These spreading pulses are related to slab rollback and are synchronous with the reduction of the subduction zone width during the formation of the narrow Calabrian arc. Using laboratory models, we investigated the long-term and transient effects of the reduction of slab width on the subduction kinematics. We found that the abrupt reduction in slab width results in a pulse of acceleration of the trench retreat velocity, as the balance between driving and resisting forces acting on the slab is temporarily modified. Our findings also show that the time scale and amplitude of spreading observed in the Tyrrhenian Sea can be experimentally fitted if the scaled viscosity of the uppermost part of the mantle ranges between 10 19 and 10 20 Pa s.

Overriding plate thinning in subduction zones: Localized convection induced by slab dehydration

Abstract: In subduction zones, many observations indicate that the backarc thermal state is particularly hot and that the upper lithosphere is thin, even if no recent extension episode has occurred. This might result from free thermal convection favored by low viscosities in the hydrated mantle wedge. We perform 2-D numerical experiments of the convective mantle wedge interaction with both the downgoing slab and the overriding plate to test this hypothesis, explore its physical mechanism, and assess its dependencies on some relevant rock properties. Water transfers across the subducting plate and the mantle wedge are explicitly modeled by including in the calculation realistic hydration/dehydration reaction boundaries for a water-saturated mantle and oceanic crust. The rheology is non-Newtonian and temperature-, pressure-, and water content-dependent. For low strength reduction associated to water content, the upper plate is locally thinned by an enhanced corner flow. For larger strength reductions, small convection cells rapidly thin the upper plate (in less than 15 Myr) over the area in the overriding lithosphere hydrated by slab-derived water fluxes. As a result, the thinned region location depends on the subducting plate thermal state, and it increases with high convergence rates and low subduction dip angles. Other simulations are performed to test the sole effect of hydrous rock weakening on the upper plate/mantle convective interaction. They show that the thinning process is not influenced by the corner flow, but develops at the favor of a decoupling level induced by the formation of hydroxylated minerals inside the hydrated lithosphere. The erosion mechanism identified in these simulations allows us to explain the characteristic duration of erosion as a function of the hydrous strength reduction. We find that the presence of amphibole in the upper lithosphere in significant proportions is required down to a temperature of about 980°C, corresponding to an initial depth of ∼70 km, to strongly decrease the strength of the base of the lithosphere and trigger a rapid erosion (<15 Myr).