Figure 1.
Systematic variation of Cu/Zr in global arc volcanic rocks and mid-ocean ridge basalts revealing that the subarc mantle is more oxidized than the mid-ocean ridge mantle
Under the support of the National Natural Science Foundation of China (Grant No.
41773025), Ph.
D.
student Zhao Siyu, associate researcher Yang Yang, researcher Zhao Taiping and foreign collaborators from the Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, and foreign collaborators have obtained research on the redox state of the mantle in the global subduction zone.
progress
.
The research results are titled "Oxidized primary arc magmas: Constraints from Cu/Zr systematics in global arc volcanics", published in Science on March 23, 2022 in Science Advances
.
Paper link: https://
.
The subduction of the oceanic plate carries a large amount of redox-sensitive valence elements such as S, Fe, and C into the interior of the earth, which drives the oxygen cycle between the earth's surface and the deep part, and is crucial to the formation and maintenance of a habitable earth
.
Current research generally confirms that arc volcanic rocks in subduction zones are more oxidized than mid-ocean ridge basalts, but whether their oxidation comes from "mantle source" (material contribution of the subducted slab to the mantle wedge) or "crust source" (the influence of the crustal evolution process) ), is still controversial
.
The difficulty in current research is that there are almost no volcanic rocks that can represent the composition of primary arc magmas, so it is difficult to fundamentally define the origin of arc volcanic oxidation
.
The redox state of the primary arc magma determines the content of the variable valence element S in the magma, thereby controlling the systematic change of the sulfide-philic element Cu in the magma
.
Based on this, the study systematically summarized and sorted out the data of more than 100,000 arc volcanic rock samples around the world.
It was found that the Cu/Zr ratio in arc volcanic rocks in different subduction zones remained constant in the early stage of magmatic evolution (Fig.
a).
For the first time, it was proposed that MgO > The Cu/Zr ratio of 6% arc volcanic rocks preserves information about their primary magma, documenting systematic changes in mantle sulfur content and redox state during partial melting of the mantle
.
Combined with the redefinition of the sulfur content in the subarc mantle, this study innovatively uses the Cu/Zr ratio of arc volcanic rocks to identify the geochemical behavior of the variable valence element S and chalcophilic elements in the global arc magma, which restricts the subarc mantle than the mid-ocean ridge mantle.
It is more oxidized (Fig.
b, Fig.
c), which confirms that the origin of arc magma oxidation comes from "mantle source"
.
This study provides a new definition for the debate on the origin of arc magma oxidation in the past decade, and provides theoretical support for understanding the oxygen cycle process between the surface and the deep part of the earth
.
