Deep mantle structure as a reference frame for movements in and on the Earth

Abstract

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...

Neo-Tethys geodynamics and mantle convection: from extension to compression in Africa and a conceptual model for obduction

“…The Madagascar-Agulhas LIP, in particular, has been present offshore South Africa from ϳ140 to 95 Ma (Gohl et al 2011). These successive volcanic events sign the presence of a long-lasting mantle upwelling underneath South Africa during a long period, also responsible for the evolution of dynamic topography in eastern Africa (Burke 1996;Moucha and Forte 2011;Torsvik et al 2014). This conclusion is further corroborated by the occurrence of kimberlites from ϳ200 to ϳ50 Ma with a younging from east to west (Jelsma et al 2009(Jelsma et al , 2004Torsvik et al 2010) suggesting that South Africa has slowly overridden the plume, before the latter migrated northward (Braun et al 2014).…”

The effect of plate motion history on the longevity of deep mantle heterogeneities

“…On the basis of the continental reconstruction model of Torsvik et al (2014), Domeier and Torsvik (2014) constructed a global plate model from 250 to 410 Ma, with 1 Ma time resolution, using continuously closing plate polygons . Unlike the maps of Scotese (e.g., 1997), the reconstructions of Torsvik et al (2014) explicitly include absolute longitude and are TPWcorrected (Fig.…”

PMTec: A new MATLAB toolbox for absolute plate motion reconstructions from paleomagnetism

“…To facilitate the effort of linking surface plate tectonics with mantle dynamic features (e.g. van der Meer et al, 2010van der Meer et al, , 2012Torsvik et al, 2014), PMTec includes a set of ancient plate boundaries primarily defined in the subduction frame of van der Meer et al (2010,2012) (Fig. 1b).…”

“…The outcome reconstructions, however, are associated with large uncertainties because of various underlying assumptions such as long-term stability of deep mantle structures (e.g. Torsvik et al, 2014).…”

“…Notably, there is a new reconstruction method gaining popularity in recent years: using sinking slabs and deep mantle structures resolved from global mantle tomography models to correct for existing plate reconstructions primarily defined in the paleomagnetic reference frame (e.g. van der Meer et al, 2010van der Meer et al, , 2012Torsvik et al, 2014). This method usually starts with reconstructions presented in the paleomagnetic reference frame, and ends up with modifying the input finite rotations using ancient subduction zones inferred from users' selected seismic tomography models.…”