Journal
EARTH AND PLANETARY SCIENCE LETTERS
Volume 454, Issue -, Pages 28-35Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.epsl.2016.08.032
Keywords
Archean seawater; strontium isotopes; barite
Categories
Funding
- NASA Astrobiology Institute
- NSF [1523697]
- National Aeronautical and Space Administration (NASA)
- Division Of Earth Sciences
- Directorate For Geosciences [1523697] Funding Source: National Science Foundation
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Controls on Archean seawater chemistry remain controversial. Many studies have suggested that it was largely controlled by oceanic hydrothermal fluid circulation. Recent work, however, from clastic sequences, Hf-O isotope data from detrital zircons, and models for the Rb/Sr evolution of the continental crust suggest that intense continental weathering and low-temperature surface alteration were more important than previously thought during the early Archean. This is consistent with biogeochemical studies that suggest the Archean had a diverse microbial ecology, which would, in part, need to be sustained by nutrients (e.g., phosphorus) that were derived from continental weathering. To further quantify continental weathering during the early Archean, we analyzed 3.26 Ga barite from the Fig Tree Group, South Africa for strontium, oxygen, and sulfur isotope compositions. We propose that the seawater component of the barite is characterized by Sr-87/Sr-86 ratios >0.701, which is significantly more radiogenic than contemporaneous mantle (similar to 0.7007-0.7008). The radiogenic nature of seawater at this time suggests that the continental weathering flux at 3.26 Ga had a large impact on ocean chemistry 400 million years earlier than previously suggested. (C) 2016 Elsevier B.V. All rights reserved.
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