Abstract:
Two equatorial, antipodal large low shear-wave velocity provinces in the lowermost mantle beneath Africa (termed Tuzo) and the Pacific Ocean (Jason) are prominent in all shear-wave tomographic models and have been argued to be related to a dominant degree-2 pattern of mantle convection that has been stable for long times. Most reconstructed large igneous provinces and kimberlites over the past 300 Myr have erupted directly above the margins of Tuzo and Jason, which we term the plume generation zones. This remarkable correlation suggests that the two deep mantle structures have been stable for at least 300 Myrs. Stability before Pangea time (prior to 320 Ma) is difficult to test with plate reconstructions because the paleogeography, the longitudinal positions of continents and the estimates of the true polar wander are uncertain for that time. It is similarly challenging to reproduce such long-term stability in numerical models. 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 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 can be successfully applied to the entire Phanerozoic. This model requires that Tuzo and Jason remain nearly stationary from the early Cambrian (540 Ma), governing in the large-scale convection within the Earth's mantle. Our Paleozoic model is a kinematic model for the continents and the next step in improving it will be developing a global model for the entire lithosphere (including synthetic oceanic lithosphere). This is challenging but essential for assessing whether our model is tectonically and geodynamically plausible and to test the longevity of Tuzo and Jason through numerical modeling.