Recent studies highlight olivine’s crucial contribution to the movement of heat throughout Earth’s mantle. In fact, this relatively obscure mineral composes some 80% of the planet’s oceanic lithosphere, a testament to its significance. This work uncovers the ways in which olivine’s remarkable properties control geodynamic processes and shape geological phenomena, such as earthquakes.
The reason for this is that Olivine is a very dense mineral and thus, the oceanic lithosphere is denser than its continental counterpart. It constitutes about 60% of the upper mantle. This layer extends from depths of 40 to 410 kilometers (25 to 255 miles) below the planet’s surface. Olivine is the most abundant mineral in Earth’s outer shell. It is crucial for thermal conductivity and heat diffusion in the mantle.
Importance of Olivine in Heat Transport
Other research indicates that radiation plays a crucial role in controlling heat transport in olivine. It makes up about 40% of the total heat dispersed in the olivine-dominated upper mantle. This surprising finding underscores just how important olivine’s radiative thermal conductivity is. It deeply influences slab heating and thereby impacts a plethora of geodynamic processes.
Olivine is unique in that it stays infrared transparent. That unique property lasts all the way down through even the extreme pressures and heat of Earth’s interior. We measured transparency as a means of exploring, for the first time, how this reality affects thermal behavior.
“We measured, for the first time, the transparency of olivine inside Earth,” – Enrico Marzotto.
The very high radiative conductivity of olivine acts to raise slab temperatures by as much as 200K. Such rapid heating can trigger the decomposing of water-carrying minerals at much shallower depths, changing the way subducting plates behave.
Implications for Subducting Plates and Water Transport
How olivine reacts with water is crucial in deciding how subducting plates behave. Only slabs older than 60 million years and sinking faster than 10 centimeters per year remain cold enough to transport water bearing minerals into the mantle transition zone (MTZ). This layer, or zone, exists between 410 to 660 kilometers deep.
According to Marzotto, this mechanism may help explain why earthquakes happen at depths greater than 70 kilometers. The chemical interaction of water with these minerals is key for understanding the source of seismic activity in subduction zones.
“Consequently, only slabs that are more than 60 million years old and sinking faster than 10 centimeters per year, remain sufficiently cold to transport the water-bearing minerals down to the mantle transition zone (MTZ) in 410 to 660 kilometers depth,” – Marzotto.
The study emphasizes that olivine’s radiative thermal conductivity not only affects the density and rigidity of these subducting plates but influences their capacity to carry water into Earth’s interior.
Advancements in Understanding Geodynamic Behavior
Researchers have developed numerical tools through this study to compute the lifetime of thermal anomalies in the mantle and their geodynamic behavior. Such tools will allow scientists to better understand how changes in heat distribution within the Earth’s mantle drive plate dynamics and contribute to natural hazards.
The combined results highlight just how much an understanding of an olivine’s role can help us better understand what’s going on inside Earth. These links are the subject of active research and investigation. Through their work, they will learn how the tectonic activity involved may have various implications for the overall dynamics of Earth’s geology.
“Our study also provides numerical tools to compute the lifetime of thermal anomalies in the mantle and their geodynamic behavior,” – Marzotto.