Redox evolution of differentiating hydrous basaltic magmas recorded by zircon and apatites in mafic cumulates: The case of the Malayer Plutonic Complex, Western Iran

Author(s)
Deevsalar, Reza
Pan, Yuanming
Shinjo, Ryuichi
Milan, Luke
Song, Ke-han
Xiao, Qunfeng
Shakouri, Mohsen
Rae-Ling Paterson, Alisa
Hu, Yongfeng
Publication Date
2023-04
Abstract
<p>Mafic-ultramafic cumulates can provide records of basaltic magma chambers' conditions and processes, which are often difficult to determine in areas dominated by crustal-derived felsic intrusions, such as the Malayer Plutonic Complex (MPC), Western Iran. New U-Pb zircon ages for mafic cumulates in the MPC confirm the presence of isolated magma chambers of contrasting compositions during Middle Jurassic. Mafic cumulates found in seven separate zones across the MPC vary from olivine gabbro to anorthosite. While the mineralogical, textural, and geochemical lines of evidence recorded in mafic cumulates indicate pH2O controls on the liquidus phases, the estimated oxygen fugacity (log<i>f</i>O<sub>2</sub>) using zircon and apatite chemistry suggests a smoothly rising redox state during the fractionation process, consistent with the trend expected for late-stages differentiation of hydrous arc magmas. This trend is further confirmed by sulfur speciation in apatites determined from microbeam sulfur K-edge X-ray absorption near edge structure (μ-XANES) spectra (S<sup>6+</sup>/ ∑S = 0.93–0.98 ~ FMQ + 2 to 0.99 ~ FMQ + 3, where ∑S = S<sup>6+</sup>+S<sup>4+</sup>+S<sup>2-</sup> ). The low S content and increasing redox state of the fractionating basaltic melts most likely resulted from preferential removal of sulfur en-route to the magma chambers along with effective assimilation of oxidizing crustal components. The reduced condition in the early basaltic melt is also evidenced by the presence of pyrite and magnetite inclusions in olivines in mafic cumulates. The shift in the prevailing <i>f</i>O<sub>2</sub> from sulfide-saturated to sulfate-bearing recorded by MPC mafic cumulates, similar to that in other magmatic arcs, is accompanied by changes in the differentiation path from transitional tholeiitic to calcalkaline.</p>
Citation
Geochemistry, 83(1), p. 1-23
ISSN
1611-5864
0009-2819
Link
Publisher
Elsevier GmbH
Title
Redox evolution of differentiating hydrous basaltic magmas recorded by zircon and apatites in mafic cumulates: The case of the Malayer Plutonic Complex, Western Iran
Type of document
Journal Article
Entity Type
Publication

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