Timing of carbonate precipitation in basalts from the Louisville seamount trail: evidence for prolonged interaction between seawater and basement

• Applicants: Dr. Elmar Albers; Professor Dr. Wolfgang Bach; Dr. Axel Gerdes
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: from 2020 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 448970447

Thick piles of sediments usually prevent seawater inflow into old oceanic crust and thus inhibit interactions between seawater and the volcanic basement. Thousands of volcanic seamounts and ocean islands, however, break through such piles of sediments. The sedimentary covers atop seamounts commonly are rather thin, which potentially allows hydrothermal fluid fluxes through seamounts and related seawater–seamount reactions to proceed for long periods of time after seamount formation. This may hence contribute to the chemical and heat exchange between oceanic basement and oceans and to regulating seawater chemistry, both of which have been found to be strongly controlled by hydrothermal fluid fluxes at or near mid-ocean ridges. However, seawater–seamount interactions have to date gained little attention and remain not well understood.We here propose a straightforward study to test if seamounts really interact with seawater over long periods of time or if the interaction ceases soon after their emplacement. We suggest to age-date carbonate materials that precipitated within four basaltic seamounts of the Louisville seamount trail, SW Pacific. The seamounts were emplaced between ~50 and 74 Ma ago and were drilled during International Ocean Discovery Program Expedition 330. We are in the possession of 59 samples that are calcitic or aragonitic vein or vesicle fill precipitates. Prior to this proposal, major and trace element as well as C, O, and Sr isotopic data have already been collected. The data indicate low-temperature (<30°C) carbonate formation with varying degrees of interaction between infiltrating seawater and the Louisville basalts. In situ U–Pb age-dating is a robust technique that will provide evidence for either of the two possibilities, i.e., if carbonates formed in narrow or wide time ranges after seamount emplacement.Further, it has previously been estimated that the yearly volume of water circulating through seamounts and ocean islands is similar to that circulating through basalts at mid-ocean ridges. Aside from providing insights into the longevity of seawater–seamount interactions, the carbonate age-dates will allow setting up first estimates on the role of seamounts as global CO2 sinks.In summary, we propose to investigate the duration of potentially significant seawater–rock interactions within oceanic seamounts as well as its direct implications on the long-term carbon cycle. The proposed work provides a direct way to identify the importance and magnitude of such interactions.

• DFG Programme: Research Grants