Earth's residual geoid is dominated by a degree-2 mode, with elevated regions above large low shear-wave velocity provinces on the core-mantle boundary beneath Africa and the Pacific. The edges of these deep mantle bodies, when projected radially to the Earth's surface, correlate with the reconstructed positions of large igneous provinces and kimberlites since Pangea formed about 320 million years ago. Using this surface-to-core-mantle boundary correlation to locate continents in longitude and a novel iterative approach for defining a paleomagnetic reference frame corrected for true polar wander, we have developed a model for absolute plate motion back to earliest Paleozoic time (540 Ma). For the Paleozoic, we have identified six phases of slow, oscillatory true polar wander during which the Earth's axis of minimum moment of inertia was similar to that of Mesozoic times. The rates of Paleozoic true polar wander (<1°/My) are compatible with those in the Mesozoic, but absolute plate velocities are, on average, twice as high. Our reconstructions generate geologically plausible scenarios, with large igneous provinces and kimberlites sourced from the margins of the large low shear-wave velocity provinces, as in Mesozoic and Cenozoic times. This absolute kinematic model suggests that a degree-2 convection mode within the Earth's mantle may have operated throughout the entire Phanerozoic.plate reconstructions | thermochemical piles T wo equatorial, antipodal, large low shear-wave velocity provinces ( Fig. 1) in the lowermost mantle (1) beneath Africa (termed Tuzo) (2) and the Pacific Ocean (Jason) are prominent in all shear-wave tomographic models (3-7) and have been argued to be related to a dominant degree-2 pattern of mantle convection that has been stable for long times (3). Most reconstructed large igneous provinces and kimberlites over the past 300 My have erupted directly above the margins of Tuzo and Jason, which we term the plume generation zones (1, 2, 5). This remarkable correlation suggests that the two deep mantle structures have been stable for at least 300 My. Stability before Pangea (before 320 Ma) is difficult to test with plate reconstructions because the paleogeography, the longitudinal positions of continents, and the estimates of true polar wander are uncertain (8). It is similarly challenging to reproduce such long-term stability in numerical models (9). However, if the correlation between the eruption sites of large igneous provinces, kimberlites, and the plume generation zones observed for the past 300 Ma has been maintained over the entire Phanerozoic (0-540 Ma), it can provide a crucial constraint for defining the longitudinal positions of continental blocks during Paleozoic time (250-540 Ma).Here we show that a geologically reasonable kinematic model that reconstructs continents in longitude in such a way that large igneous provinces and kimberlites are positioned above the plume generation zones at the times of their formation ( Fig. 2A and SI Appendix, Fig. S2) can be successfully defined f...

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[1] The resolution operator R is a critical accompaniment to tomographic models of the mantle. R facilitates the comparison between conceptual three-dimensional velocity models and tomographic models because it can filter these theoretical models to the spatial resolution of the tomographic model. We compute R for the tomographic model S20RTS (Ritsema et al., 1999(Ritsema et al., , 2004 and two companion models that are based on the same data but derived with different norm damping values. The three models explain (within measurement uncertainty) S-SKS and S-SKKS travel times equally well. To demonstrate how artifacts distort tomographic images and complicate model interpretation, we apply R to (1) a thermochemical and (2) an isochemical model of convection in the mantle that feature different patterns of shear velocity heterogeneity in the deep mantle if we assume that shear velocity heterogeneity is caused by temperature variations only. R suppresses short-wavelength structures, removes strong velocity gradients, and introduces artificial stretching and tilting of velocity anomalies. Temperature anomalies in the thermochemical model resemble the spatial extent of low seismic velocity anomalies and the shear velocity spectrum in the D'' region better than the isochemical model. However, the thermochemical model overpredicts the amplitude of shear velocity variation and places the African and Pacific anomalies imperfectly. We suspect that inaccurate velocity scaling laws and uncertain initial conditions control these mismatches. Extensive hypothesis testing is required to identify successful models.Citation: Ritsema, J., A. K. McNamara, and A. L. Bull (2007), Tomographic filtering of geodynamic models: Implications for model interpretation and large-scale mantle structure,

Advances in global seismic tomography have increasingly motivated identification of subducted lithosphere in Earth's deep mantle, creating novel opportunities to link plate tectonics and mantle evolution. Chief among those is the quest for a robust subduction reference frame, wherein the mantle assemblage of subducted lithosphere is used to reconstruct past surface tectonics in an absolute framework anchored in the deep Earth. However, the associations heretofore drawn between lower mantle structure and past subduction have been qualitative and conflicting, so the very assumption of a correlation has yet to be quantitatively corroborated. Here we show that a significant, time‐depth progressive correlation can be drawn between reconstructed subduction zones of the last 130 Myr and positive S wave velocity anomalies at 600–2300 km depth, but that further correlation between greater times and depths is not presently demonstrable. This correlation suggests that lower mantle slab sinking rates average between 1.1 and 1.9 cm yr−1.

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