Slab

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

A New Slab Model Approach for Electronic Structure Calculation of Polar Semiconductor Surface

Abstract: A new slab model approach is examined for the electronic structure calculation of a polar semiconductor surface. Our proposed slab model contains fractionally charged H atoms which completely terminate a noninteresting surface of the slab. We have studied in detail the electronic structure of the polar GaAs(001) surface in order to examine the reliability of our slab model. Calculation is performed by the ab initio pseudopotential method. We have found that our slab model can accurately describe a polar semiconductor surface. In addition, this model can greatly reduce the computational time.

Local and regional variations in Central American arc lavas controlled by variations in subducted sediment input

Abstract: The sedimentary section (at DSDP Site 495) on the subducting Cocos Plate has large stratigraphic changes in incompatible elements and element ratios, the result of early carbonate deposition followed by late hemipelagic deposition. Lavas from Central America define both local and regional geochemical trends that reflect the strong influence of the two Cocos Plate sediment units. Element ratios with large stratigraphic variations on the Cocos Plate (e.g. Ba/Th, U/La) define local variations within individual volcanic centers in Central America, indicating that marine stratigraphy controls some geochemical characteristics of the lavas. These local trends can be explained by changing the proportions of hemipelagic sediment input into the magma generation process. These local trends are observed in all the segments of the arc, regardless of the intensity of the slab signature. Regional variations are most clearly seen in element ratios that are nearly constant through the Cocos Plate sediment stratigraphy (e.g. Ba/La, U/Th), suggesting that regional variations reflect differences in the intensity of the flux from the subducting slab. The slab signal is strongest in Nicaragua and along the volcanic front. The signal decreases to the northwest and southeast of Nicaragua and toward the back arc. The large slab signature in the lavas from western Nicaragua occurs in the area with the thinnest continental crust and steepest dip of the slab. The mass flux of incompatible elements into the system is easily estimated, except for elements, like Pb, that have high and variable abundances in the basaltic oceanic crust section. The mass flux of elements out of the system depends on eruption rates, which are variable along the arc and only approximately known. Comparison of input and output fluxes for five different segments of the arc reveals that some elements (K, B, Cs, and Rb) are very efficiently delivered to the volcanoes from the subducted slab. Other elements (Sr, Ba, and U) are returned to the surface with moderate efficiency, whereas some elements (REEs) may come mostly from the mantle wedge with minor slab contribution. The relative order of recycling efficiencies of incompatible elements implies that a hydrous fluid dominates the transfer of material from the slab to mantle.

Mantle convection with plates and mobile, faulted plate margins.

Abstract: A finite-element formulation of faults has been incorporated into time-dependent models of mantle convection with realistic rheology, continents, and phase changes. Realistic tectonic plates naturally form with self-consistent coupling between plate and mantle dynamics. After the initiation of subduction, trenches rapidly roll back with subducted slabs temporarily laid out along the base of the transition zone. After the slabs have penetrated into the lower mantle, the velocity of trench migration decreases markedly. The inhibition of slab penetration into the lower mantle by the 670-kilometer phase change is greatly reduced in these models as compared to models without tectonic plates.

Towards absolute plate motions constrained by lower-mantle slab remnants

Abstract: The movement of tectonic plates before the Cretaceous period is poorly understood. A global mantle tomography model suggests that the longitude of oceanic subduction zones up to 300 million years ago was offset by up to 18∘ compared with tectonic reconstructions for the same period.