Eruption Sites of LIPs of the Past 250 My With Respect to the slow/fast D" Boundary in Four Improved Reference Frames

We have shown (Burke and Torsvik 2004) that nearly all of the Large Igneous Provinces (LIPs) erupted on the Earth's surface during the past 250 My rose, at the time of their eruption, from the base of the mantle close to the 1 percent slow S-wave delta V contour of the D" zone. Here we report on the use of (1) Improved plate-circuitry (among PAC-ANT-AUS-MADAGAS-IND-SOAM-AFR) and (2) upgraded paleomagnetic data-sets to confirm and refine our results. In an attempt to establish whether rotation of LIPs to their sites at eruption can be used to learn something about mantle and core behavior over the past 250 My we have performed rotations on assumptions of: (1) a persistent geocentric axial magnetic dipole field, (2) a time-dependent non-dipole (octopole) magnetic field contribution (Torsvik and Van der Voo (2002), (3) a mantle wind contribution to mantle flow (Steinberger et al. 2004) and (4) a revised (new timescale) fixed hot-spot (no mantle wind) reference frame. Our test consisted of estimating how closely radials dropped from rotated LIP sets based on these four assumptions plotted to the 1 percent slow contour derived from seismic tomography. We compared S-wave tomographic models at the CMB and opted to use the SMEAN model (Becker and Boschi 2002) recognizing that other models are similar and that all have similar limitations. The mean deviation of the projected rotated LIPs from the 1 percent slow contour is 6 degrees at the CMB. The four different assumptions yield results between 6.5 and 5.5 degrees which seems unlikely to be a significant difference. Our conclusion is that it is not yet possible to discriminate among the four models of mantle and core behavior using our procedure. Becker, T.W and Boschi, L. 2002: A comparison of tomographic and geodynamic mantle models. Geochemistry, Geophysics, Geosystems 3, 2001GC000168. Burke, K. and Torsvik, T.H. 2004: Derivation of large igneous provinces of the past 200 million years from long-term heterogeneities in the deep mantle. Earth Planet Sci. Lett. 227, 531-538. Steinberger, B., Sutherland, R. and O'Connell, R.J. 2004: Prediction of Emperor-Hawaii seamount locations from a revised model of plate motion and mantle flow. Nature 430, 167-173. Torsvik, T.H. and Van der Voo, R. 2002: Refining Gondwana and Pangea Palaeogeography: Estimates of Phanerozoic (octupole) non-dipole fields. Geophysical Journal International 151, 771-794.