The theory of plate tectonics explains how major landforms and phenomena such as mountains, volcanoes, and earthquakes, are formed by the subterranean movement of geologic plates. Plate tectonics are also responsible for driving old crust sitting on the margins of oceans down to the earth’s mantle. As this process goes on, the minerals change in response to rising temperatures. Cubic CaSiO3 perovskite, a major phase in subducted oceanic crust, is one of these minerals. It is formed some 550km from the majority garnet. Until a new study, cubic CaSiO3 perovskite’s rheological properties were unknown. The study suggests that it is a weak phase at the lower mantle’s temperature and could possibly be the weakest lower-mantle phase, an estimated 1,000 times weaker than bridgmanite and ferropericlase.

The Importance of the Study

The study is important because it gives us some insight as to what happens as we get deeper into the earth. It’s clear that a study like this faces enormous technical challenges, and that any information we get about the earth’s deepest subterranean processes is very important. Understanding the mechanics of these rocks gives us information about how slabs behave as they sink deep into the earth. 

The Theory of Plate Tectonics 

The theory of plate tectonics went mainstream in the 1960s as data came in supporting the idea of continental drift, which was first proposed by Alfred Wegener in 1912. Continental drift explains how, 200 million years ago, Pangaea, a supercontinent, started to break up, with fragments drifting away to form today’s continents.That theory evolved into the theory of plate tectonics, which explains the formation of land masses such as the San Andreas Fault, East African Rift and the Himalayas, as well as formations beneath our oceans. This process is also responsible for the formation of different materials, such as gold, the darling of investors active in gold investments.

The most important bit of evidence in support of continental drift showed that the ocean bed had an enormous mountain range encircling the planet. This “mid-ocean ridge” was believed by Harry Hess to be the result of molten rock emerging from the asthenosphere. As it rose to the surface, it cooled, forming crust and causing seafloor spreading along a divergent plate boundary. After millions of years, this crust disappeared into the ocean’s trenches in subduction zones. 

Cubic CaSiO3 perovskite

What we know from there we get from reading seismic waves that result from earthquakes, travelling at different speeds through varying materials. The different speeds tell us that there has been a change. The Low Shear Velocity Province (LLSVP), which sits at the boundary between the core and mantle, is one of the great mysteries of the earth’s geologic processes. There are two LLSVP, one underneath the Pacific and the other below Africa. One question that had troubled scientists was what kind of rock makes up the mantle. We now know the answer: cubic CaSiO3 perovskite. Studying it proved difficult because it cannot be studied at room pressure. It thrives under high temperature and pressure. Without that, it becomes glass. The research team not only solved this problem, they discovered that it is 1,000 times softer than the rest of the mantle.