| Insights into the composition and thermal structure of the upper mantle beneath multiple regions are made possible by various seismological techniques and additional constraints provided by gravity and mineral physics. I investigate the upper mantle beneath the Colorado Rockies, Sierra Nevada and New Zealand. In each region I find complicated compositional and thermal structure. The southwest Colorado Rockies are marked by a region of reduced shear wave speeds which many have believed are due to increased temperatures. I add the complementary measurement of shear wave attenuation and conclude, with the help of gravity, that southwest Colorado is underlain, not by increased temperatures, but by anomalous composition, specifically a small fraction of phlogopite. When investigating the Sierra Nevada, I again find multiple regimes of temperature and composition. Without the complementary measurement of attenuation, low velocities would have been misinterpreted as upwelling asthenosphere. I found however, that these low velocities actually reflect an unusual eclogite, a rock that is typically seismically fast. In New Zealand, through the use of receiver functions, I image the subducting Pacific Plate and its influence on the transition zone discontinuities. This influence depends strongly on temperature, composition, and the kinetics of mineral phase reactions. Whereas the deflection of the 660 km discontinuity appears consistent solely with the expected changes in temperature due to the subducting slab, the topography on the 410 km discontinuity is more complicated and requires multiple operating mechanisms to explain its behavior. |
