Introduction: Water is thought to be vital for the development of plate tectonics because it lowers viscosities in the asthenosphere and enables subduction. However, the following issue persists: if water is necessary for plate tectonics, but subduction itself hydrates the upper mantle, how is the upper mantle initially hydrated? Here we present models demonstrating that processes associated wi...

Oxygen and iron isotope analyses of low-Ti and high-Timare basalts are presented to constrain their petrogenesis and to assess stable isotope variations within lunar mantle sources. An internally-consistent dataset of oxygen isotope compositions of mare basalts encompasses five types of low-Ti basalts from the Apollo 12 and 15 missions and eight types of high-Ti basalts from the Apollo 11 and 1...

I apply array processing techniques to study the slowness and coda of P/Pdiff for 1,371 shallow earthquakes (< 200 km) that occurred in Asia, South America, Tonga-Fiji, and Indonesia, and were recorded by the medium-aperture array, YKA, in Canada. The slowness analysis shows lateral variations in Earth structure at the base of the mantle across the north Pacific. I observe an Ultra-Low Velocity...

[1] Subduction zones alter the upper plate in a variety of ways, including metasomatism via slab-derived fluids and accretion of exotic terranes. These processes should produce distinctive seismic signatures, as seismic velocities are sensitive to compositional variations. A new method is developed to estimates depths to interfaces and Poisson’s ratio (Vp/Vs ratio) for dipping layered structure...

In Africa volumetrically minor, mid-plate volcanic rocks of Cenozoic age are concentrated in areas affected by Pan-African (500 _+ 150 Ma) crustal reactivation, and are virtually absent from cratonic areas. We interpret this as indicating that Pan-African areas are underlain by fertile lithospheric mantle and cratons by depleted lithospheric mantle, and propose a model to explain both the distr...

Molluscs fabricate shells of incredible diversity and complexity by localized secretions from the dorsal epithelium of the mantle. Although distantly related molluscs express remarkably different secreted gene products, it remains unclear if the evolution of shell structure and pattern is underpinned by the differential co-option of conserved genes or the integration of lineage-specific genes i...

[1] We investigate the physics of multiscale convection in Earth’s mantle, characterized by the coexistence of large-scale mantle circulation associated with plate tectonics and smallscale sublithospheric convection. In part 2 of our study, the temporal and spatial evolution of sublithospheric convection is studied using two-dimensional whole mantle convection models with temperatureand depth-d...

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...