Isotopic signatures of extinct low-temperature hydrothermal chimneys in the Jaroso Mars analog

摘要

The present work presents a geochemical study, focused on the oxygen and carbon isotopic signatures of shallow-marine, carbonate extinct chimneys, from Jaroso Hydrothermal System (JHS). In each chimney a meticulous sampling from the central orifice to the outer rim of the structure was performed. The isotopic geochemistry study allowed to establish the origin and evolution of the fluids during the formation of the vent structures. The negative δ~(13)C values indicate a source of meteoric water for the Fe-rich fluids. More positive δ~(13)C values are present in ankerite and in some calcite, both related with marine water. δ~(18)O in ankerite indicates low-temperature hydrothermal conditions, while in calcite is showing either primary signatures or early diagenesis at low temperature. On the contrary, calcite displaying more negative δ~(13)C and δ~(18)O values represents a late mineral phase which was formed under meteoric diagenesis. Each chimney resulted from the precipitation of intergranular carbonate cement around a channellized flux of metal-rich fluid crossing a shallow-marine, unconsolidated, sandy-marl substrate. The paleoenvironmental interpretation carried out from the isotopic data emphasizes the importance of the stable isotopes as fluid geomarkers, also advancing in the understanding of an interesting analog for the geological and astrobiological exploration of Mars.