Brief Bio: John Tarduno holds a Ph.D. in geophysics from Stanford (1987). He is currently Kenan Professor and Chair of the Department of Earth and Environmental Sciences, and Professor of Physics and Astronomy, at the University of Rochester. Professor Tarduno’s research focuses on the history of Earth’s magnetic field applied to geodynamics and evolution of the core, mantle and planetary habitability. He has been a Guggenheim fellow (2006), and is a fellow of AGU, AAAS and GSA. Professor Tarduno was awarded the RAS Price Medal and EGU Petrus Peregrinus Medal.
Abstract: Hotspots were once thought to be the surface manifestation of plumes fixed in the deep mantle. Fixity meant hotspots could be used as a frame of reference for plate motions. This paradigm appeared in nearly all introductory geology textbooks for decades. Often, these descriptions were complemented with a figure of the great bend in the Hawaiian-Emperor hotspot track of the northern Pacific plate. The bend illustrated a ~60 degree change in plate motion in the hotspot reference frame. The hypothesis predicts that all volcanic edifices that comprise a hotspot track should have formed at the same latitude, given by the present-day location of the hotspot. Paleomagnetic data of radiometrically-dated volcanic rocks comprise the gold standard for tests, and the results of ocean drilling expeditions have played a prominent role. Instead of recording a constant latitude, analyses of basalts recovered from the Emperor Seamounts reveal a trend of decreasing paleolatitude with time, indicating a rate of motion greater than 40 cm/yr of the Hawaiian plume in Earth’s mantle. During this interval of rapid southward Hawaiian hotspot drift, paleomagnetic data from the Louisville chain from the southern Pacific plate show only limited latitudinal motion. These observations suggest a further, simple consistency test: if the Hawaiian hotspot had moved rapidly southward while the Louisville hotspot moved only slowly, the distance between seamounts of the same age comprising each track should decrease with time. Radiometric data of Paleogene age from the volcanic chains confirm this prediction. Thus, not only are hotspots not fixed, but the dominant reason for the distinct bend morphology in the Hawaiian-Emperor track is hotspot motion rather than plate motion. A leading bottom-up process calls upon the deep mantle interaction of the Hawaiian plume with the Pacific Large Low Shear Velocity Province (LLSVP). This plume-LLSVP interaction suggests that LLSVPs, while long-lived, should not be taken as fixed. Instead, as is indicated by paleomagnetic data, they can appear to move at rates similar to plates as they are continually deformed and reshaped by mantle circulation and plume formation.