Paleomagnetic data provide one of the few probes available to interrogate early evolution of the core. Here we apply this probe by examining the latitudinal dependence of paleosecular variation (PSV) data derived from high-quality paleomagnetic data collected from Proterozoic and Neoarchean rocks. These data define a Neoarchean geomagnetic field that was more dipolar than that during Proterozoi...

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...

The surface of Venus is so hot that the lower crust may be weak enough to allow decoupling of mantle and crust. An analytic model of such decoupling assumes that the shallow mande forms the top boundary layers of large scale mantle convection cells. Crustal flow is driven by the motion of the marie and by topographically induced pressure gradients. The model predicts that the lowest lowlands ar...

[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 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...

Spectrum analyses were made of the records of the short-period vertical component of P and PcP phases on seismograms of array stations at Tonto Forest, Arizona, for twenty-one earthquakes over the range A _-47 ø to 83 ø. Generally, as has been reported by other investigators, the trace amplitude ratio of PcP to P is significantly larger than the theoretical ratio. The pulse width of PcP is narr...

The amount of heat flowing from Earth's core critically determines the thermo-chemical evolution of both the core and the lower mantle. Consisting primarily of a polycrystalline aggregate of silicate perovskite and ferropericlase, the thermal boundary layer at the very base of Earth's lower mantle regulates the heat flow from the core, so that the thermal conductivity (k) of these mineral phase...

[1] Convective mixing in the fluid outer core can induce rapid transient decrease of the geomagnetic dipole. Here we determine rates of dipole moment decrease as a function of magnetic Reynolds number following convective instability in a numerical dynamo and in axisymmetric kinematic flows. Our calculations show that mixing flows induce reversed magnetic flux on the core-mantle boundary throug...

Paleomagnetic data provide one of the few probes available to interrogate early evolution of the core. Here we apply this probe by examining the latitudinal dependence of paleosecular variation (PSV) data derived from high-quality paleomagnetic data collected from Proterozoic and Neoarchean rocks. These data define a Neoarchean geomagnetic field that was more dipolar than that during Proterozoi...