Laboratory studies on deformation of olivine in response to applied stress suggest two distinct deformation mechanisms in the earth’s upper mantle: diffusion creep through diffusion of atoms along grain boundaries and dislocation creep by slipping along crystallographic glide planes. Each mechanism has very different and important consequences on the dynamical evolution of the mantle and the de...

[1] Much progress has been made over the past several decades in delineating the structure of subducting slabs, but several key aspects of their dynamics remain poorly constrained. Major unsolved problems in subduction geodynamics include those related to mantle wedge viscosity and rheology, slab hydration and dehydration, mechanical coupling between slabs and the ambient mantle, the geometry o...

The mechanisms that drive the upwelling of chemical heterogeneity from the lower to upper mantle (e.g., thermal versus compositional buoyancy) are key to our understanding of whole mantle convective processes. We address these issues through a receiver function study on new seismic data from recent deployments located on the Afar Triple Junction, a location associated with deep mantle upwelling...

The surface of Mars consists of an old, heavily cratered and elevated southern hemisphere and younger, resurfaced and depressed northern hemisphere, a feature often termed the crustal dichotomy. The global crustal structure [Zuber et al., 2000] revealed by topography and gravity data from the Mars Global Surveyor spacecraft, and the possible late formation of the boundary zone between the hemis...

We utilize earthquake recordings at two broadband seismographs located on the coast of the Gulf of Mexico to estimate Q of the mantle wedge. From the data at a station situated in the Laguna Verde nuclear power plant (LVIG), about 100 km northwest of Veracruz, and at the eastern edge of the Mexican Volcanic Belt, we estimate an upper bound of shear-wave Q of the mantle wedge, Q( f ) 120f 0.75 (...

BACKGROUND AND PURPOSE The properties of the cement mantle around a prosthesis are important. We investigated whether the surgical approach to the hip influences the quality and thickness of the cement mantle when using a straight femoral stem design. METHODS In a consecutive multi-surgeon series, we reviewed the radiographs of 270 patients after cemented Exeter total hip arthroplasty. 135 st...

Introduction Ocean island basalts (OIB) are thought to sample the Earth’s deep mantle, whereby thermochemical plumes entrain lower mantle material and bring it to the surface where it erupts. By measuring the isotopic compositions of global OIB—which record the isotopic compositions of OIB mantle sources—geochemists can “map” the isotopic heterogeneity of the Earth’s deep mantle (e.g., Gast et ...

Study of commercially produced volcanic CO2 gas associated with the Colorado Plateau, USA, has revealed substantial new information about the noble gas isotopic composition and elemental abundance pattern of the mantle. Combined with published data from mid-ocean ridge basalts, it is now clear that the convecting mantle has a maximum (20)Ne/(22)Ne isotopic composition, indistinguishable from th...

Seismic refraction, gravity, phase velocity, and magnetic data, coupled with the geologic record, are all approximately satisfied by the structure shown in Fig. 9. A 20-kilometer crust under the Coast Ranges and Great Valley thickens to more than 30 kilometers under the Sierra Nevada and parts of the Basin and Range province; this whole area is underlain by an anomalous upper mantle with a velo...