HR: 08:30h
AN: T31B-03    [PDF]
TI: Mantle flow, mantle plumes and hotspot motion: The cause of the bend of the Hawaiian hotspot track
AU: * O'Connell, R J
EM: oconnell@geophysics.harvard.edu
AF: Harvard University, 20 Oxford St, Cambridge, MA 02138 United States
AU: Steinberger, B
EM: bernhard@jamstec.go.jp
AF: IFREE, JAMSTEC, 2-15 Natsushima-cho, Yokosuka-shi, 237-0061 Japan
AU: Sutherland, R
AF: Inst Geological and Nuclear Sciences, PO Box 30368, Lower Hutt, 6315 New Zealand
AB: Flow in the mantle has been modelled using seismically inferred density anomalies in the mantle and recent plate motions. Using past plate motions and advecting the density anomalies backward in time allows the models to be extended back to $\sim100$ My. The flow distorts and moves mantle plumes, causing the hotspots to move. Previous models of this by Steinberger and O'Connell have predicted the southward motion of the Hawaiian hotspot. Recently published paleomagnetic results by Tarduno et al [Science, 301,1064(2003)] have confirmed this prediction, and refined models have reproduced the measured motion of the hotspot. A related problem is the plate circuit that connects the African and Pacific hotspots: The Hawaiian hotspot track predicted from published plate circuits, assuming stationary hotspots, does not fit the observed track. The discrepancy steadily increases for the Hawaiian chain, and the predicted track does not show a bend. Our model of plumes distorted by global mantle flow can explain the misfit for times after the bend. For the Hawaiian hotspot, computations consistently predict a S to SE motion of about 1000 km during the past 80 Ma, which explains the discrepancy for the Hawaiian chain, although not the bend and the trend of the Emperor chain. However, a combination of modeled hotspot motion and a relatively modest motion at an unrecognized plate boundary --- about 13 degrees clockwise rotation of W vs. E Antarctica around an axis near the E--W--Antarctic boundary between $\sim$ 83 and 44 Ma, plus possibly some deformation between the Pacific plate and the Campbell Plateau between $\sim$ 83 and 63 Ma --- allows a simultaneous fit to all hotspot tracks from $\sim$ 83 to 47 My. The required deformation is not in conflict with, but supported by geologic evidence. The motion, and its cessation, may be related to tractions on the base of the plates (which are also calculated from the flow models), and the growth of strong oceanic lithosphere that inhibited the separate motion after 47 My ago.
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8121 Dynamics, convection currents and mantle plumes
DE: 8158 Plate motions--present and recent (3040)
SC: Tectonophysics [T]
MN: 2003 Fall Meeting