A recent study published in the scientific journal Nature Geoscience has shed light on the role of plate tectonics in the exchange of elements between the atmosphere, earth’s surface, and the deep mantle. The study found that oxygen played a significant role in this process, particularly in the formation of ore deposits.
Researchers analyzed magmas from before and after a major event called the Great Oxidation Event (GOE) and observed a shift from reduced to more oxidized magmas. This shift was a result of oxidized sediments being subducted into the mantle through weathering and erosion processes. The recycling of these sediments provided atmospheric access to the mantle, leading to changes in the mantle’s composition.
Lead author Hugo Moreira emphasized the significance of these findings, stating that they provide new insights into the geological evolution of the earth and the interconnectedness of the deep earth and its mantle with atmospheric changes. The study deepens our understanding of the relationship between external and internal reservoirs of the earth.
To analyze the sulfur state in minerals, the research team utilized the ID21 beamline at the European Synchrotron Radiation Facility in France. They examined two-billion-year-old zircon crystals from the Mineiro Belt in Brazil, which acted as time capsules preserving their original composition. The analysis revealed that minerals formed before the GOE had a reduced sulfur state, while those formed after the event showed increased oxidation levels.
“Mantle oxygen fugacity, which measures oxygen’s ability to drive chemical reactions in magmas, is crucial for understanding volcanic activity and ore formation,” explained Moreira. “However, until now, we lacked a reliable method to track changes in this parameter for ancient parts of earth’s history.”
Moreira also noted that sulfur speciation and magma fugacity are dynamic parameters that can change throughout a magma’s journey from formation to crystallization. While the study considered factors like pressure and temperature, further analysis is required to trace the complete path of fugacity from magma generation to final crystallization.
Co-author Craig Storey expressed enthusiasm for the study’s implications, highlighting the new avenues of research it opens. He emphasized the importance of understanding the earth’s ancient past and its connection to the development of our atmosphere. The study prompts questions about the evolution of magma types over time and the intricate interplay between plate tectonics and atmospheric cycles.
