Plate tectonic control of strontium concentration in Phanerozoic and Neoproterozoic seawater: Evidence from fluid inclusions in marine halite

Chemical analyses of 1371 fluid inclusions in 131 halite samples with marine 87Sr/86Sr values were used to reconstruct the strontium concentrations [Sr]SW of Phanerozoic and Neoproterozoic seawater. [Sr]SW varied seven-fold and oscillated twice between high-and low-Sr concentrations over the past 550 million years (Myr), in rhythm with Ca-rich and SO4-poor paleoseawater intervals and calcite-aragonite seas. Variations in the [Sr]/[Ca]SW ratio from fluid inclusions were not significant over the past-270 Myr, and are within +/- 3 lmol/mmol of the modern [Sr]/[Ca]SW ratio of-8.5 lmol/mmol. These results agree with the [Sr]/[Ca]SW ratios obtained from fossil corals, benthic foraminifera, brachiopods, belemnites, and rudists. [Sr]/[Ca]SW in the early and middle Paleozoic was-2 times the modern [Sr]/[Ca]SW ratio. A major shift of the [Sr]/[Ca]SW ratio in the late Permian coincided with the initial rifting of the Pangean supercontinent. Seawater 87Sr/86Sr ratios plotted against 1/[Sr]SW show two distinct linear correlations: negative correlation from 515 to 252 Ma and positive correlation from 150 to 0 Ma, suggesting different controls on the global Sr cycle between these intervals. The negative correlation coincides with the long-term assembly of Pangea in the Paleozoic (-500-250 Ma). The positive correlation from 150 to 0 Ma par-allels the break-up of Pangea and the decrease of mid-ocean ridge (MOR) hydrothermal fluid flux and subduction zone length in the Mesozoic and Cenozoic.(c) 2023 Elsevier Ltd. All rights reserved.

Automated summary

Chemical analyses of fluid inclusions in halite samples were used to study the strontium concentrations in ancient seawater over the past 550 million years. The results show variations in strontium concentrations and ratios in seawater, with oscillations between high and low concentrations. These variations are related to changes in paleoseawater conditions and the presence of different mineral phases. The study also reveals different controls on the global strontium cycle during different time intervals.