Halite fluid inclusion geochemistry of evaporite deposits in central Iran

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International Union of Geodesy and Geophysics (IUGG)
The chemical analyses of major ions in primary halite fluid inclusions is widely used for the determination and characterization of brine chemistry and its evolution in ancient evaporite basins through the Phanerozoic (eg. Ayora et al., 2001; Brennan and Lowenstein, 2002; Horita et al., 2002; Kovalevich et al., 2002). The purpose of this study is to show the major ion compositional evolution and halite crystallization pathway in the Miocene, M1 member of the Upper Red Fm. (N, Great Kavir Basin, Iran). We show how the Rift setting of the Great Kavir Basin, exerted the main control on the modification of seawater major ion chemistry. Influx of Ca-Cl2 brines modified the earlier evaporated seawater into Ca- Mg- Na- Cl brines. In this case, the Ca2+ concentration of the evolving brine exceeded overall concentrations of SO42-, HCO3-, and CO32- ions, which is expressed as mCa2+>Σ(mSO42- + mHCO3- + mCO32-). From this modified brine MgSO4-poor potash salts (mainly halite, sylvite and carnallite) precipitated. The study of major ion variation for evaporite deposits in the mentioned area reveals that the evaporation path in the Great Kavir Basin was not the same as present-day seawater. The geochemical diagrams (e.g. Mg vs. SO4 and K) show that major ions followed different evolution trends. Seemingly, an externally Ca-Cl2 influx would have overridden the chemical signature of evaporated seawater within Great Kavir Basin. As a result, sylvite instead of K-Mg-sulfates precipitated, similar to that observed in other rift settings such as the Danakil Depression (Ethiopia) in Quaternary evaporates where secular seawater compositional changes can not justified the observed lithologies. Ayora C., Cendn D. I., Taberner C., and Pueyo J. J. (2001) Brine-mineral reactions in evaporite basins: Implications for the composition of ancient oceans. Geology 29(3), 251-254. Brennan S. T. and Lowenstein T. K. (2002) The major-ion composition of Silurian seawater. Geochimica et Cosmochimica Acta 66(15), 2683-2700. Horita J., Zimmermann H., and Holland H. D. (2002) Chemical evolution of seawater during the Phanerozoic: Impliations from the record of marine evaporites. Geochimica et Cosmochimica Acta 66(21), 3733-3756. Kovalevich V. M., Peryt T. M., Beer W., Geluk M., and Halas S. (2002) Geochemistry of Early Triassic seawater as indicated by study of Rt halite in the Netherlands, Germany and Poland. Chemical Geology 182, 549-563.
Halite, Iran, Geochemistry, Evaporites, Fluids, Inclusions
Shariatinia, Z., Cendón, D. I., Pueyo, J. J., Rahimpour-Bonab, H., & Hezarhani, A. (2007). Halite fluid inclusion geochemistry of evaporite deposits in central Iran. Poster presented to the IUGG XXIV2007 General Assembly – “Earth: Our Changing Planet”, 2nd – 13th July 2007. In L. Ubertini, P. Manciola, S. Casadei, & S. Grimaldi (Eds.), Earth: Our Changing Planet. Proceedings of IUGG XXIV General Assembly, (pp. 1727). Perugia, Italy: University of Perugia.