Researchers have been studying the formation of the Earth’s oldest continental crust, which is approximately 4 billion years old. It was previously believed that the entire planet was covered by one complete lithospheric crust. However, new research suggests that this crust may have formed through the movement of Earth’s major surface plates over billions of years, a process known as plate tectonics.
There are two main theories regarding the formation of continental crust. One theory involves the subduction of one plate beneath another, which results in partial melting and changes in the composition of magma. The other theory focuses on mechanisms within the crust itself, unrelated to plate boundaries, that also lead to partial melting.
In a recent study published in Nature Geoscience, researchers conducted experiments on primitive oceanic plateau basalts from the Pacific Ontong Java Plateau. They found that continental crust could not form at pressures occurring up to 50km depth. This indicates that such magmas formed during convergent subduction zones, suggesting the existence of plate tectonics 4 billion years ago.
Plate tectonics plays a crucial role in erosion, deposition, mountain formation, and volcanic activity, which are all involved in the formation of continental crust. The release of gases from volcanic activity, particularly carbon monoxide and methane, may have also played a role in the initiation of life on Earth.
Notably, the silica-rich continental crust found on Earth has also been identified in smaller volumes on Mars and Venus, providing insight into the role of plate tectonics in the wider solar system.
The researchers also investigated the stability of various minerals at different pressures and temperatures to determine at which point they transformed. They found that garnet and rutile were not stabilized at 1.4GPa, indicating that subduction is a more suitable mechanism to explain the formation of continental crust.
Modeling suggests that early magmas underwent fractional crystallization as they rose through the crust, resulting in the formation of different crystal compositions. Amphibole crystallization was identified as a major driver in partial melting, and it may have been incorporated into the crust through overturning and burial.
Overall, this research provides valuable insights into the formation of the Earth’s oldest continental crust and the role of plate tectonics in shaping our planet.
Sumber (tanpa URL):
– Alan R. Hastie et al, Deep formation of Earth’s earliest continental crust consistent with subduction, Nature Geoscience (2023).
– Allen P. Nutman, Forming the oldest-surviving crust, Nature Geoscience (2023).