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.