Caltech UT Austin CSEDI Project

The CSEDI Fine Structure of the Lower Mantle Project

The lower mantle plays a fundamental role in the thermal and chemical evolution of the planet. A large fraction of the heat and heat producing elements ultimately driving the engine responsible for plate tectonics reside in the lower mantle. The boundary between the core and mantle is a primary interface within the deep interior and seismologists have revealed that the mantle side of this boundary (D") is extraordinarily complex with a myriad of fine structure. Thermal and chemical heterogeneity, anisotropy, and melting within the lower mantle may all be required in order to explain this observed fine structure. This strongly suggests that the lower boundary of the mantle is as complex as the mantle's top boundary. In order to make accelerated progress toward understanding the dynamics and fine structure of the lower mantle and D" region, we propose to undertake collaborative research where seismological and geodynamic tools and concepts are used in an integrated fashion. Geodynamic models will be used to study the dynamics of strong, cold slabs interacting with thermo-chemical boundary layers and the details of hot regions on the CMB where there may be partial melting, entrainment of core material into the mantle, or reaction of the mantle with the molten core. These thermo-chemical fields will be mapped into two and three-dimensional seismic velocity models from which we will calculate synthetic waveforms. Pre-existing and newly collected waveforms will be compared with the synthetic waveforms thereby allowing us to test a variety of dynamic models. Seismology will be integrated with geodynamics at large scales. With global flow models, we will determine geographically where slabs are most likely to accumulate and construct maps of the CMB showing expected thermal anomalies. In conjunction with fully dynamic models, we will predict the geographic distribution of fine structure. Different kinds of thermo-chemical boundary layers will predict different distributions of seismic fine structure. Guided by this geographic approach, we will then collect critical waveform data to further refine our understanding of the dynamics of this extraordinarily important and complex region of the Earth. We will address the following questions: ¥ What dynamic models of thermo-chemical boundary layers are consistent with both seismic fine structure within D" and the geographic distribution of seismic fine structure ? ¥ What thermo-chemical dynamic models are consistent with the very slow velocity anomaly under the long wavelength Central Pacific slow anomaly ? ¥ Are seismological observations of D" consistent with the segregation of oceanic crust from the rest of the subducting lithosphere ? ¥ What kind of constraints do geodynamical models which are consistent with seismological structure place on mixing rates ? Are there any implications for geochemical models for the evolution of the mantle ?