Under the Sierra Nevada in California, scientists have observed a rare phenomenon that sheds light on the dynamics of the Earth's crust.
The rocks of the lithosphere, denser than the underlying mantle, can sink into it, a process called delamination. This long-debated theory finds confirmation through research conducted under the Sierra Nevada in California.
View from the International Space Station (ISS) showing the Sierra Nevada mountains (California) formed by delamination of the Earth's crust beneath them.
Image NASA
Vera Schulte-Pelkum and Deborah Kilb used seismic waves to study the lower crust and upper mantle beneath the Sierra Nevada. Their analysis reveals a band of seismicity at unusual depths, indicating an ongoing delamination process.
The seismic data shows a distinct layer in the mantle, less pronounced in the north. This supports the hypothesis that part of the lithosphere under the southern Sierra sank millions of years ago, a phenomenon that could spread northward.
The presence of deep earthquakes in the central Sierra is explained by the ability of cold continental lithosphere to fracture. These findings align with previous studies on the structure of the Earth's crust in this region.
This research provides tangible evidence of a major geological process, offering new insights into the formation and evolution of continents. The Sierra Nevada proves to be a natural laboratory for studying these phenomena.
Scientists estimate that delamination under the Sierra Nevada has been ongoing for at least 3 million years. This study highlights the importance of understanding the internal mechanisms of our planet to better grasp its geological history.
What is lithospheric delamination?
Lithospheric delamination is a geological process where a portion of the lithosphere, the Earth's rigid outer layer, detaches and sinks into the underlying mantle. This phenomenon occurs when the lithosphere becomes denser than the mantle, often due to cooling processes or chemical composition.
This process plays a crucial role in the formation and evolution of continents. It allows for the recycling of Earth's crust materials into the mantle, influencing plate tectonics and mountain formation.
Delamination can also explain certain types of deep earthquakes, such as those observed under the Sierra Nevada. These earthquakes result from the fracturing of cold and rigid lithosphere, rather than the plastic deformation typical of hot materials.
Understanding this process helps scientists better interpret seismic data and reconstruct the geological history of affected regions. It opens new perspectives on the internal dynamics of our planet.
How do seismic waves reveal the Earth's structure?
Seismic waves, generated by earthquakes or explosions, travel through the Earth and are modified by the different layers they encounter. These modifications allow scientists to deduce the composition and structure of the Earth's internal layers.
The receiver function technique, used in this study, analyzes how seismic waves change as they pass through the boundaries between different geological layers. This allows for precise mapping of the interfaces between the crust and the mantle.
By studying variations in seismic data, researchers can identify specific geological structures, such as layers of lithosphere sinking into the mantle. This method is essential for understanding complex geodynamic processes.
Advances in seismic data analysis, combined with comprehensive earthquake catalogs like ComCat, offer a unique window into the Earth's internal processes. This allows for a better understanding of the mechanisms of continent and mountain formation.