What are the mysterious structures observed in the lower mantle?

I learned of very interesting results related to geology. The Dailymail popular article (see this) tells about massive structures in the Earth’s deep mantle below Pacific Ocean near the mantle-core boundary. The article “Full-waveform inversion reveals diverse origins of lower mantle positive wave speed anomalies” of Schouten et al published in Scientific reports (see this) describes the findings.

There are cold regions deep within the Earth where seismic waves behave in unexpected ways. The chemical composition can involve heavy elements in these regions. These in-homogenities lead to the increase of the sound velocity. These regions, located 900 to 1,200 kilometers beneath the Pacific Ocean, defy expectations based on conventional plate tectonics theories. These kinds of structures can result from the subduction of continental plates leading to the sinking of a plate to the mantle. There are however no subduction records in the Ocean regions so that the mechanism must be different.

It seems that the recent view of the dynamics of the Earth’s mantles is in a need of a profound updating. It has been proposed that the structures could be the remnants of ancient, silica-rich materials from the early days of the Earth when the mantle was formed billions of years ago. Alternatively, they may be areas where iron-rich rocks have accumulated over time due to the constant movement of the mantle. However, researchers are still unsure about the exact composition of these deep Earth structures.

Here is the abstract of the article of Schouten et al.

Determining Earth s structure is paramount to unravel its interior dynamics. Seismic tomography reveals positive wave speed anomalies throughout the mantle that spatially correlate with the expected locations of subducted slabs. This correlation has been widely applied in plate reconstructions and geodynamic modelling. However, global travel-time tomography typically incorporates only a limited number of easily identifiable body wave phases and is therefore strongly dependent on the source-receiver geometry.

Here, we show how global full-waveform inversion is less sensitive to source-receiver geometry and reveals numerous previously undetected positive wave speed anomalies in the lower mantle. Many of these previously undetected anomalies are situated below major oceans and continental interiors, with no geologic record of subduction, such as beneath the western Pacific Ocean. Moreover, we find no statistically significant correlation positive anomalies as imaged using full-waveform inversion and past subduction. These findings suggest more diverse origins for these anomalies in Earth s lower mantle, unlocking full-waveform inversion as an indispensable tool for mantle exploration.

Here some terminology is perhaps in order. Seismic waves are acoustic waves and their propagation in the mantle is studied. Positive speed anomaly means that sound speed is higher than expected. The lowering of temperature or increase of density such as presence of iron, silica, or magnesium can cause this kind of anomalies. The Pacific ocean and the interior regions of plates do not have any subduction history so that the slabs cannot be “slabs” as pieces of continental plates, which have sunk to the mantle.

Why these findings are interesting from the TGD point of view is that TGD suggests that the Cambrian Explosion roughly 500 million years ago was accompanied by a rather rapid increase of the Earth’s radius by factor 2 (see this), this and this). In the TGD inspired cosmology, the cosmic expansion occurs as rapid jerks and Cambrian Explosion would be associated with this kind of jerk. This sudden expansion would have broken the crust to pieces and led to the formation of oceans as the underground oceans bursted to the surface. The multicellular life evolved in the underground oceans would have bursted to the surface and this could explain the mysterious sudden appearance of complex multicellular life forms in the Cambrian Explosion. In this event tectonic plates and subduction would have emerged.

I have not earlier considered what happened in the lower mantle in the sudden expansion of Earth. Did these kinds of cracks occur also in the mantle-core boundary and lead to the formation of the recently observed structures also below regions where there is no geologic record for subduction? Could at least some regions which are believed to be caused by the sinking of parts of continental plates have such structure?

See the article Expanding Earth Hypothesis and Pre-Cambrian Earth.

For a summary of earlier postings see Latest progress in TGD.

For the lists of articles (most of them published in journals founded by Huping Hu) and books about TGD see this.