Geochemical and petrological characterization of listwaenite from Oman and Iran ophiolites: implications for hydrothermal carbonation and silicification alteration processes

Abstract

Listwaenites (carbonated/silicified ultramafic rocks) are widely spread in the Semail Ophiolite of Oman, mainly in Fanja rea and in Islam Abad area of the Neyriz Ophiolite of Iran. Listwaenite is gaining worldwide interest due to their possible economic value as gold bearing rocks and assessing the global carbon sequestration and flux. This work presents new petrographic and geochemical data of listwaenite from Fanja and Islam Abad area and estimates the physical and chemical conditions of their formation. Three types of listwaenite are known to occur within ophiolites worldwide, and these include silica-, carbonate-, and silica-carbonate. Typical minerals which are usually known to occur in these listwaenite include dolomite, ankerite, calcite, magnesite, quartz, iron oxides, relict chromite grains ± talc and serpentine. Calcite- and magnesite-dolomite listwaenite is more abundant in the Fanja area, while dolomite listwaenite is more abundant in Islam Abad area. The major element chemistry of the different types of listwaenite in both Fanja and Islam Abad area is largely similar to that of altered ultramafic rocks and listwaenites from other ophiolites occurrences. In comparison to the primary mantle and chondrite spider diagrams, the Islam Abad listwaenite shows higher trace and REE elements abundance than those from the Fanja area. The variable and high abundances of Ca, Mg, Ba, Zr, Sr, Pb, Zn, Mo, and W in the carbonate- and silica-carbonate listwaenite indicate a hydrothermal source from the sedimentary and metamorphic units of the Arabian Platform underlaying the listwaenite. Depletion and enrichment of major and trace elements in the listwaenite are indicative of large fluctuations in major and trace element mobility, where listwaenite preserves different stages of gradual alteration of their ultramafic protoliths. The listwaenite content of CaO, SiO₂, and MgO depends on the stage of listwaenite formation, in which carbonate listwaenite is formed in the first stage, progressing to silica-carbonate listwaenite in the final stage. The listwaenite in Islam Abad and Fanja area was altered to different stages by hydrothermal alteration of serpentinite and harzburgite along Late Cretaceous thrust and Paleocene-Miocene extensional faults and shear zones, which acted as pathway for trace elements and Ca and/or Si rich fluids at different times probably during subduction and/or post obduction stages.