In a recent study by the MTA FI Lendület Pannon LitH2Oscope Research Group at the ELKH Research Institute of Earth Physics and Space Sciences (FI), researchers have presented a possible hypothesis that could contribute to a better understanding of global plate tectonic processes and a more accurate description of geological carbon emissions. An article on the topic has been published in the journal Global and Planetary Change.
More than 50 years after the birth of modern plate tectonic theory, it is not entirely clear what physicochemical processes cause the difference between the lithosphere, the rock envelope of the earth's crust and the rigid solid part of the upper mantle, and the plastic asthenosphere below (Figure 1, LAB), and what the driving forces are that cause the outer, brittle lithosphere to move on top of the asthenosphere. In addition, in recent decades, geophysical methods have been used to discover interfaces (Figure 1, MLD) within the continental lithosphere at depths of around 100 km that may play a significant role in the detachment and subsidence of the lower rock cover (delamination) as zones of weakness.
Delamination plays a significant role in the formation of plate footings (subductions) and raises the possibility that the subduction considered characteristic of ocean plates may even begin within continents. Zones of weakness within the continental lithosphere may also play a role in the 'rejuvenation' of the lithosphere of particularly thick and older shields. This is because the very deep roots of the shields can become detached along the zones of weakness, causing a significant thinning of the lithosphere, as has been shown in eastern China, for example.
The researchers describe how the stability of small amounts of volatile – primarily water – and aqueous minerals – primarily pargasite – depending on the age and temperature of continental lithospheres, may explain the contrast between the lithosphere-asthenosphere and the creation of zones of weakness at a depth of 100 km in the case of the older and colder continental lithospheres. This suggests that it is also conceivable that it is the volatile substances in the depths of the planet that make the Earth a living planet in tectonic terms.
The researchers' hypothesis also makes it possible to interpret the origin of CO2-rich 'magmatic' uplifts on the surface in a tectonic environment where there is no longer active volcanism. The essence of this idea is that the source of CO2 is the cooling asthenosphere itself, in which the crystallization of the small quantity of silicate melt present leads to the formation of CO2-rich fluids that are highly mobile toward the surface. CO2-rich surface discharges of this origin have so far not been given sufficient weight in the description of the global CO2 cycle, but may now also play an important role in more accurate quantitative modeling of climate change.
More information about the research group can be found here.