The chemical evolution of Precambrian seawater: Evidence from REEs in banded iron formations

Journal Article · Thu Nov 01 00:00:00 EST 1990 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(90)90114-Z· OSTI ID:6026651

Derry, L A; Jacobsen, S B ^[1]

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1. Harvard Univ., Cambridge, MA (USA)

The authors present REE patterns determined by isotope dilution mass spectrometry from 20 Precambrian banded iron formation (BIF) samples, ranging in age from 3.4 to 0.65 Ga. The samples studied represent a variety of depositional settings and sedimentary facies. The oxide facies BIFs typically show LREE depleted patterns relative to shales, with (La/Nd){sub N} {ge} 1 and (La/Yb){sub N} mostly 0.3-0.8. The NASC-normalized REE patterns from the oxide facies BIFs are similar to modern metalliferous sediments, except for Ce and Eu. Positive Eu anomalies were found in all BIF samples, whereas Ce anomalies were variable. Both the oxide facies BIFs and modern metalliferous sediments typically have La/Yb ratios slightly higher than seawater. The REE data suggest that the Fe and REEs in BIFs coprecipitated from seawater as Fe oxy-hydroxides. The variable Ce anomalies are probably the result of diagenetic processes and redox cycling, similar to modern reducing environments. Comparison of mass balance estimates for REEs in the oceans based on Nd isotopic composition and on Eu anomalies results in a large discrepancy, which probably is a result of non-conservative behavior of Eu during mining of hydrothermal waters with ambient seawater. The REE data are consistent with a model for BIFs in which Fe and REEs derived from submarine hydrothermal systems are upwelled from the deep ocean, mixing with oxidizing surface water (with some continentally derived REEs), and deposited on the continental margins.

• OSTI ID: 6026651
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Vol. 54:11; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

15 GEOTHERMAL ENERGY
58 GEOSCIENCES
HYDROTHERMAL SYSTEMS
REDOX REACTIONS
ROCK-FLUID INTERACTIONS
IRON ORES
CHEMICAL COMPOSITION
DIAGENESIS
GEOCHEMISTRY
ISOTOPE RATIO
PACIFIC OCEAN
SEAWATER
CERIUM ISOTOPES
DEPOSITION
EUROPIUM ISOTOPES
GEOLOGIC HISTORY
ISOTOPE DILUTION
LANTHANUM ISOTOPES
MASS BALANCE
MASS SPECTROSCOPY
NEODYMIUM ISOTOPES
PETROCHEMISTRY
PRECAMBRIAN ERA
RARE EARTHS
THERMAL WATERS
YTTERBIUM ISOTOPES
CHEMICAL REACTIONS
CHEMISTRY
ELEMENTS
ENERGY SYSTEMS
GEOLOGIC AGES
GEOTHERMAL SYSTEMS
HYDROGEN COMPOUNDS
ISOTOPE APPLICATIONS
ISOTOPES
METALS
ORES
OXYGEN COMPOUNDS
RARE EARTH ISOTOPES
SEAS
SPECTROSCOPY
SURFACE WATERS
TRACER TECHNIQUES
WATER
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