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

• Published in: Geochimica et cosmochimica acta Vol. 346; pp. 165 - 179
• Main Authors: Weldeghebriel, Mebrahtu F., Lowenstein, Tim K., Xia, Zhiguang, Li, Weiqiang
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.04.2023
• Subjects: Aragonite-calcite seas; Fluid inclusions; Halite; LA-ICP-MS; Seawater chemistry; Supercontinent cycle; Halite; Seawater chemistry; LA-ICP-MS; Supercontinent cycle; Aragonite-calcite seas; Fluid inclusions
• ISSN: 0016-7037; 1872-9533
• DOI: 10.1016/j.gca.2023.02.009

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 µmol/mmol of the modern [Sr]/[Ca]SW ratio of ∼8.5 µmol/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 parallels 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.