Fall 2010 Colloquium Abstracts - Ed Garnero

October 13, 2010

Observed and Inferred Multi-Scale Circulation on Earth: From the Surface to the Center (and Back)

Ed Garnero (Arizona State University)

For many decades scientists have documented current and past movements of Earth’s tectonic plates, that is, the rigid outer shell of our planet, some 100+ km thick. In some regions (e.g., mid-ocean ridges) plates are born, in others (subduction zones), they submerge back into the interior. How do subducting slabs drive and/or relate to general circulation of the mantle? On the other hand, Earth’s interior is still quite hot (e.g., 4000 deg K nearly ½ way to the center at the core-mantle boundary), and over geological time scales the viscous rock mantle convects and churns – how does this process relate to pushing the tectonic plates around? To pursue these questions, we use the tool of seismology in an attempt to image the interior directly, and then to make sense of these findings with guidance from the fields of geodynamics and mineral physics, especially in a planetary perspective. I will show some recent results that argue for a dynamically and chemically complex internal structure of our planet, but in a story that is not entirely confusing. In fact, geographical relationships between surface observables and internal structures paint a picture of a fairly organized system. For example, large dense chemical reservoirs at the base of the mantle are shaped by downwelling subduction-related currents, and mantle plumes are formed near the sides or edges of these piles. I will present this work along with new ideas for generating mega plumes that might be related to massive eruptions that cause large igneous provinces (and more, really!). I will try to put these findings into a planetary perspective.