Aftabi, Alijan and Atapour, Habibeh (2018) Comment on the papers by Hovland et al. (2018) “Large salt accumulations as a consequence of hydrothermal processes associated with 'Wilson cycles': A review” (part 1 and 2). Marine and Petroleum Geology, 98 . pp. 890-897. DOI 10.1016/j.marpetgeo.2018.09.006.

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Abstract

Highlights

• Major types of evaporites are of solar origin.
• Minor hydrothermal evaporites are linked to submarine hydrothermal fluids.
• Hydrothermal evaporites show volcanogenic feeder zone and alteration mineralogy.
• Mg/Ca-Cl and Mg/Ca-Na/Cl diagrams separate hydrothermal evaporites from solar ones.
• A new global map highlights the marine, non-marine and hydrothermal evaporites.

Abstract

The geological model of large hydrothermal salt accumulations linked to "Wilson cycles" as reviewed by Hovland and Coworkers, un-adequately addressed: (1) the lack of well exposed submarine volcanogenic hydrothermal feeder zone, (2) the sequential precipitation of different hydrothermal evaporite minerals and (3) the absence of hydrothermal alteration mineralogy around the major evaporites. These aforementioned points are the main classical features to be linked to the hydrothermal model of evaporites. Experimentally, heating seawater during submarine volcanism firstly results in precipitation of anhydrite followed by halite, other evaporite minerals, serpentine, brucite, talc, metallic sulfides-oxides and related hydrothermal alterations. In this regard, Mg/Ca – Cl, Mg/Ca – SO4, Mg/Ca – Na/Cl and Mg/Ca - TDS biplots show that hydrothermal brines of riftogenic and subduction zone settings plot in a separate field than the subduction-related Andean Salars as well as seawater. This indicates that the hydrothermal serpentinization of basaltic oceanic crust and mantle peridotites removes magnesium from seawater and incorporates the Mg into serpentine, brucite and other hydrous Mg-silicates rather than the hydrothermal brines. Finally, our comment arose from a recent global classification of the most distinguished marine, non-marine and exhalative hydrothermal evaporites.

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