GP24A-01 16:10h
Hotspot motion, scales of mantle convection and the long-term history of the geodynamo
The Hawaiian-Emperor hotspot track has a prominent bend which has served as the basis for the theory that the Hawaiian hotspot, fixed in the deep mantle, traced a change in plate motion. However recent data from ODP Leg 197 define an age-progressive paleolatitude history, indicating that the Emperor seamount trend was principally formed by the rapid motion of the Hawaiian hotspot (81 to 47 Ma). Recognition of this motion affects models of mantle convection and plate tectonics and our understanding of terrestrial dynamics. For the future, the study demonstrates how paleomagnetism can be used to record large-scale mantle flow. Defining the nature of this flow is an important prerequisite to our understanding of core-mantle boundary processes, and their ultimate relationship with the geomagnetic field. While great progress has been made understanding secular variation and reversal frequency, long-term paleointensity records have remained elusive. Studies of feldspars containing magnetic inclusions indicate that the mid-Cretaceous field was remarkably strong, stable and dipolar. Superchrons may represent times when the nature of core-mantle heat flux allows the geodynamo to operate at peak efficiency. On billion-year time scales, spanning initiation of inner core growth, the paleomagnetic record is sparse. The use of lasers to derive directions and paleointensities from oriented silicate minerals holds significant promise for understanding the nature of the Archean geodynamo and its potential relationship with environmental conditions of the early Earth.
http://www.earth.rochester.edu/pmag/