Ultralow Oxygen Fugacity in Peridotites Reveals Deep, Hot, and Ancient Melting Events

แนวคิดหลัก

Peridotites from the Gakkel Ridge and East Pacific Rise record oxygen fugacity (fO2) more than four orders of magnitude below the mantle average, indicating ancient, high-temperature melting events.

บทคัดย่อ

The study examines the petrography and geochemistry of peridotites from the Gakkel Ridge and East Pacific Rise, including 16 new high-precision determinations of oxygen fugacity (fO2). The key findings are:

1. Refractory peridotites from the Gakkel Ridge record fO2 more than four orders of magnitude below the mantle average.
2. Thermodynamic and mineral partitioning modeling shows that such excursions to ultralow fO2 can be produced by large degrees of melting at high potential temperature (Tp), beginning in the garnet field and continuing into the spinel field.
3. These conditions were met during the generation of ancient komatiites but not modern basalts.
4. This does not mean that the ambient convecting upper mantle had a lower ferric to ferrous ratio in Archaean times than today, nor that modern melting in the garnet field at hotspots produces reduced magmas.
5. Instead, it implies that rafts of ancient, refractory, ultrareduced mantle continue to circulate in the modern mantle while contributing little to modern ridge volcanism.

สถิติ

The oxygen fugacity (fO2) of convecting upper mantle recorded by ridge peridotites varies by more than four orders of magnitude.
Refractory peridotites from the Gakkel Ridge record fO2 more than four orders of magnitude below the mantle average.

คำพูด

"Refractory peridotites from the Gakkel Ridge record fO2 more than four orders of magnitude below the mantle average."
"Excursions to ultralow fO2 can be produced by large degrees of melting at high potential temperature (Tp), beginning in the garnet field and continuing into the spinel field—conditions met during the generation of ancient komatiites but not modern basalts."

ข้อมูลเชิงลึกที่สำคัญจาก

Deep, hot, ancient melting recorded by ultralow oxygen fugacity in peridotites - Nature

by Suzanne K. B... ที่ www.nature.com 07-24-2024

https://www.nature.com/articles/s41586-024-07603-w

สอบถามเพิ่มเติม

How might the presence of these ancient, ultrareduced mantle rafts affect the geochemistry and dynamics of the modern mantle?

The presence of ancient, ultrareduced mantle rafts circulating in the modern mantle can have significant implications for its geochemistry and dynamics. These rafts, characterized by ultralow oxygen fugacity conditions, represent pockets of refractory material that have undergone extensive melting at high potential temperatures. As these rafts interact with the convecting upper mantle, they can introduce unique geochemical signatures and elements into the mantle system. The circulation of these ultrareduced mantle domains can influence the overall redox state of the mantle, potentially leading to variations in the oxidation state of magmas generated at mid-ocean ridges. Additionally, the presence of these ancient mantle rafts may impact mantle dynamics by introducing heterogeneities that can affect mantle flow patterns and melt generation processes.

What other geochemical signatures might be used to identify and trace the origins of these ancient mantle domains?

In addition to oxygen fugacity, several other geochemical signatures can be utilized to identify and trace the origins of these ancient mantle domains. Isotope geochemistry, including radiogenic isotopes such as Sr, Nd, and Pb isotopes, can provide valuable information about the age and source of mantle rocks. The presence of certain trace elements, such as highly siderophile elements (HSEs) like platinum and palladium, can also serve as tracers for ancient mantle domains. Furthermore, the mineralogical composition of peridotites, including the presence of specific minerals like olivine, pyroxenes, and spinel, can offer insights into the petrogenesis and history of these mantle rocks. By combining multiple geochemical signatures, researchers can construct a more comprehensive understanding of the origins and evolution of these ancient mantle domains.

Could the ultralow oxygen fugacity conditions recorded in these peridotites provide insights into the redox state of the early Earth's mantle and the evolution of the atmosphere-mantle system over geological time?

The ultralow oxygen fugacity conditions recorded in peridotites from the Gakkel Ridge and East Pacific Rise have the potential to offer valuable insights into the redox state of the early Earth's mantle and the evolution of the atmosphere-mantle system over geological time. By studying the variations in oxygen fugacity within these mantle rocks, researchers can infer the prevailing redox conditions that existed during the formation of these peridotites. The ultralow fO2 values observed in these samples suggest the presence of ancient, ultrareduced mantle material that has been preserved over geological time. This preservation of ultrareduced conditions may reflect the redox state of the early Earth's mantle and provide clues about the processes that influenced the evolution of the atmosphere-mantle system. By analyzing the geochemical data from these peridotites, scientists can reconstruct the redox history of the mantle and gain insights into the interactions between the Earth's interior and its atmosphere throughout Earth's history.