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- Title
Fe–Mg Isotopes Trace the Mechanism of Crustal Recycling and Arc Magmatic Processes in the Neo‐Tethys Subduction Zone.
- Authors
Chen, Long; Li, Dong‐Yong; Deng, Jiang‐Hong; Li, San‐Zhong; Somerville, Ian; Chen, Yi‐Xiang; Zhao, Zi‐Fu; An, Wei; Li, Xiao‐Hui
- Abstract
There has been intense debate on the mechanism of crustal recycling in subduction zones, and Fe–Mg isotopes may provide new constraints on this issue. This study reports Fe–Mg isotope data for mafic plutonic rocks from the eastern and central Gangdese arc, along with their associated trench sediments in southern Tibet. The δ26Mg values of the eastern Gangdese arc rocks show negative correlations with (87Sr/86Sr)i and (206Pb/204Pb)i values, but positive correlations with εNd(t) and εHf(t) values. Conversely, the δ56Fe values of the eastern Gangdese arc rocks show positive correlations with (87Sr/86Sr)i and (206Pb/204Pb)i values, but negative correlations with εNd(t) and εHf(t) values. The Mg and Fe isotopic compositions of the central Gangdese arc rocks are comparable with those of the eastern ones, but they do not correlate with Sr–Pb–Nd–Hf isotopic compositions. Notably, the Fe–Mg isotopic compositions of most arc rocks fall between those of local trench sediments and the mantle wedge. Combined qualitative analyses and quantitative simulations suggest that: (a) the Fe–Mg isotope variations observed in the eastern Gangdese arc rocks highlight the important role of source mixing between sediment‐derived melts and peridotite, whereas (b) the Fe–Mg isotope variations observed in the central Gangdese arc rocks reflect the superposition of carbonated serpentinite‐derived Mg‐rich fluids‐peridotite source mixing and source melting. The strong correlations between Fe–Mg isotope ratios and traditional geochemical tracers provide further evidence for the recycling of crustal materials in subduction zones via various types of slab‐derived fluids and melts. Plain Language Summary: Currently, there is an ongoing debate surrounding the mechanism of transporting subducting slab‐derived materials to fuel magmatism in subduction zones. The stable isotopes of iron and magnesium—major constituents in arc rocks—are considered potential tools to resolve this dispute. However, establishing a direct link between the Fe–Mg isotopic compositions of arc rocks and specific transporting mechanisms has proven challenging. Thus far, no significant correlations have been observed between Fe–Mg isotope ratios and traditional tracers for slab materials in arc rocks, such as radiogenic Sr–Pb–Nd–Hf isotope ratios. Further complicating matters, obtaining Fe–Mg isotopic data for subducting sediments in certain subduction zones is often difficult. In this study, we simultaneously analyzed the Fe–Mg isotope compositions of the Gangdese arc rocks and their associated valuable trench sediments. For the first time, our findings unveil strong correlations between Fe–Mg and Sr–Pb–Nd–Hf isotopic compositions in arc rocks. This finding, from the viewpoint of the isotopic composition of major elements, provides new evidence for the transport of crustal materials from the subducting slab to the mantle wedge sources via various types of fluids and melts rather than by mechanically mixed solids. Key Points: The Fe–Mg isotopic compositions of the Gangdese arc mafic plutonic rocks are closely connected to their associated trench sedimentsGood correlations between Fe–Mg isotope ratios and radiogenic Sr–Pb–Nd–Hf isotope ratios are found in mafic arc rocks for the first timeFe–Mg isotopes provide further evidence for crustal recycling in subduction zones via various types of slab‐derived fluids and melts
- Subjects
TIBET (China); SUBDUCTION zones; ISOTOPES; IRON isotopes; MAGNESIUM isotopes; STABLE isotopes; GEOTHERMAL ecology; PLAINS; ORE deposits; HYDROTHERMAL deposits
- Publication
Journal of Geophysical Research. Solid Earth, 2023, Vol 128, Issue 9, p1
- ISSN
2169-9313
- Publication type
Article
- DOI
10.1029/2023JB026778