Mineral physics observations suggest that distinct density and rheological differences exist between the crustal component of oceanic lithosphere and the underlying mantle. We have conducted numerical experiments to investigate the influence of both density and viscosity on the effectiveness of recycling of oceanic crust into the lower mantle. Confirming previous results, the density inversion ...

The exposure of 1300 meters of upper oceanic crust at the Blanc0 Fracture Zone allows near-bottom gravity measurements to determine the in situ density of the seafloor as a function of depth. Gravity measurements along the north wall of the Blanc0 Depression indicate an outcrop density of 2530 * Kg/m3 for the upper 800 meters of crust and a calculated porosity of 23%. The lower 500 meters of cr...

Recycled oceanic crust, with or without sediment, is often invoked as a source component of continental and oceanic alkaline magmas to account for their trace-element and isotopic characteristics. Alternatively, these features have been attributed to sources containing veined, metasomatized lithosphere. In melting experiments on natural amphibole-rich veins at 1.5 gigapascals, we found that par...

S U M M A R Y The structure of the oceanic crust conforms in general to a very simple model. However, fine-scale variations of this structure in anomalous regions (such as beneath oceanic islands) remain poorly resolved. Here we examine teleseismic receiver functions (RFs) computed at four permanent broadband seismic stations on islands in the Pacific region. The RF method is ideal for examinin...

The effect of transition regions between continental and oceanic structures on the propagation of L, waves from continental sources is examined. In particular, the attenuation due to variations in layer thickness in such transition regions is calculated and explained for a suite of simple models. The measured attenuation, due tq the geometry of the transition regions between the oceanic and con...