Slab

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

Whole-Mantle Convection and the Transition-Zone Water Filter

Abstract: Because of their distinct chemical signatures, ocean-island and mid-ocean-ridge basalts are traditionally inferred to arise from separate, isolated reservoirs in the Earth's mantle. Such mantle reservoir models, however, typically satisfy geochemical constraints, but not geophysical observations. Here we propose an alternative hypothesis that, rather than being divided into isolated reservoirs, the mantle is filtered at the 410-km-deep discontinuity. We propose that, as the ascending ambient mantle (forced up by the downward flux of subducting slabs) rises out of the high-water-solubility transition zone (between the 660 km and 410 km discontinuities) into the low-solubility upper mantle above 410 km, it undergoes dehydration-induced partial melting that filters out incompatible elements. The filtered, dry and depleted solid phase continues to rise to become the source material for mid-ocean-ridge basalts. The wet, enriched melt residue may be denser than the surrounding solid and accordingly trapped at the 410 km boundary until slab entrainment returns it to the deeper mantle. The filter could be suppressed for both mantle plumes (which therefore generate wetter and more enriched ocean-island basalts) as well as the hotter Archaean mantle (thereby allowing for early production of enriched continental crust). We propose that the transition-zone water-filter model can explain many geochemical observations while avoiding the major pitfalls of invoking isolated mantle reservoirs.

The subducted component in island arc lavas: constraints from Be isotopes and B–Be systematics

Abstract: Although high concentrations of beryllium-10 and boron are taken as unequivocal indicators of the contribution of subducting plates, controversy persists about the processes by which material is transferred from slabs to the sources of arc magmas. Data on (10)Be/Be and B/Be ratios from four arcs suggest that the contribution from the slab is compositionally homogeneous in each arc and that subducted boron is not stored in the sub-arc mantle. The link between subduction and magma-tism at convergent margins seems to be well regulated.

Pairing an epsilon-negative slab with a mu-negative slab: resonance, tunneling and transparency

Abstract: Here, we analyze the transverse-magnetic (TM) wave interaction with a pair of slabs, one being an epsilon-negative (ENG) layer in which the real part of permittivity is assumed to be negative while its permeability has positive real part, and the other being a mu-negative (MNG) layer that has the real part of its permeability negative but its permittivity has positive real part. Although the wave interaction with each slab by itself has predictable features, we show that the juxtaposition and pairing of such ENG and MNG slabs may, under certain conditions, lead to some unusual features, such as resonance, complete tunneling, zero reflection and transparency. The field distributions inside and outside such paired slabs are analyzed, and the Poynting vector distributions in such structures are studied. Using equivalent transmission-line models, we obtain the conditions for the resonance, complete tunneling and transparency, and we justify and explain the field behavior in these resonant paired structures. Salient features of the tunneling conditions, such as the roles of material parameters, slab thicknesses, dissipation, and angle of incidence are discussed. The analogy and correspondence between the ENG-MNG pair and the pair of a slab of conventional material juxtaposed with a "double-negative" medium is also discussed. Finally, a conceptual idea for a potential application of such a "matched" lossless ENG-MNG pair in "ideal" image displacement and image reconstruction is proposed.

Global compilation of variations in slab depth beneath arc volcanoes and implications

Abstract: [1] The location and motion of subducting plates relative to volcanic arcs provide a first-order constraint on theories of arc magmagenesis We compile volcano-specific subduction parameters for 33,000 km of the global arc system at 839 volcanic centers, measuring the depth to the top of the slab (H) beneath each volcano The compilation also includes estimates of slab strike and dip, incoming plate velocity, and age, all available in accompanying auxiliary material The slab geometry is contoured from the top surface of Wadati-Benioff zones (WBZs) for a variety of teleseismic and local seismicity catalogs, which provides a reference surface for evaluating the distribution of seismicity within subducting plates The WBZ thickness exceeds that expected from hypocentral errors in a manner correlating with plate age, indicating that old plates have thicker regions in which earthquakes can occur When averaged over 500-km-long arc segments, H ranges from 72 to 173 km with a global average of 105 km, increasing by 20 km when hypocentral error effects are taken into account These depths correlate poorly with most subduction parameters, but significant correlations exist between H and slab dip (correlation coefficient is 054 for 45 arc segments) The dip correlation can be explained if the melting region is displaced from the Wadati-Benioff zone by a constant-thickness boundary layer For the north Pacific, H varies inversely with descent rate; this trend may reflect the manner in which wedge thermal structure affects arc location Over short distances some arc segments exhibit abrupt variations in arc location but not slab geometry, indicating that upper-plate tectonic processes also exert control on H These along-strike trends in H also correlate with geochemical proxies for the degree of melting, at least in one test case Thus slab geometry and kinematics provide an important control on the melting that produces arc volcanoes