Roberta L. Rudnick

University of California, Santa Barbara


Election Year: 2010
Primary Section: 15, Geology
Secondary Section: 16, Geophysics
Membership Type: Member

Research Interests

I am a geochemist who uses observations from a wide array of Earth Science disciplines to determine the average composition of continental crust and understand how continents form. Earth is the only planet in our solar system with continents, comprised of relatively low-density, SiO2-rich continental crust, and an underlying mantle "lid". Determining the composition of the continental crust is important because it contains much of the Earth's heat-producing elements (K, Th and U). Knowing the concentrations of these elements in the crust helps to determine what remains in the rest of the Earth, where they provide the energy for plate tectonics. The continental crust has an average composition of "andesite" -- a relatively silica-rich igneous rock that is unlikely to form by melting of the mantle. This observation leads to the fundamental problem that the building blocks of the continents (mantle-derived basalts) do not match the edifice (andesite). With my students and collaborators I have been systematically testing hypotheses advanced to explain the origin of this unusual crust. For example, we have shown that portions of the SiO2-depleted lower continental crust may have gravitationally separated and sunk into the deeper mantle, leaving behind more SiO2-rich crust. We are currently seeking to quantify the degree to which weathering has influenced the composition of the continental crust.

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