U, Th, and Pb isotopes in hot springs on the Juan de Fuca Ridge

Journal Article · Sat Oct 10 00:00:00 EDT 1987 · J. Geophys. Res.; (United States)

DOI:https://doi.org/10.1029/JB092iB11p11411· OSTI ID:5608449

Chen, J H

The concentrations and isotopic compositions of U, Th, and Pb in three hydrothermal fluids from the Juan de Fuca Ridge were determined. The samples consisted of 10.2--57.6% of the pure hydrothermal end-members based on Mg contents. The Pb contents of the samples ranged from 34 to 87 ng/g, U from 1.3 to 3.0 ng/g, and Th from 0.2 to 7.7 pg/g. These samples showed large enrichments of Pb and Th relative to deep-sea water and some depletion of U. They did not show coherent relationships with Mg, however, indicating nonideal mixings between the hot hydrothermal fluids and cold ambient seawater. Particles filtered from these hydrothermal fluids contained significant amounts of Th and Pb which may effectively increase the concentration of these elements in the fluids when acidified. The /sup 234/U//sup 238/U values in all samples show a /sup 234/U enrichment relative to the equilibrium value and have a seawater signature. The Pb isotopic composition of the Juan de Fuca hydrothermal fluids resembles that of 21 /sup 0/N East Pacific Rise and has a uniform mid-ocean ridge basalt signature. The hydrothermal systems at oceanic spreading ridges have circulated through a large volume of basalts. Therefore Pb in these fluids may represent the best average value of the local oceanic crust. From the effects of U deposition from seawater to the crust and Pb extraction from rock to the ocean, the U/Pb ratio in the hydrothermally altered oceanic crust may be increased significantly. copyright American Geophysical Union 1987

• Research Organization: The Lunatic Asylum of the Charles Arms Laboratory, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena
• OSTI ID: 5608449
• Journal Information: J. Geophys. Res.; (United States), Vol. 92:B11
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
GEOTHERMAL FLUIDS
ISOTOPE RATIO
PACIFIC OCEAN
VENTS
HYDROTHERMAL ALTERATION
LEAD ISOTOPES
SEA-FLOOR SPREADING
SEAWATER
THORIUM ISOTOPES
URANIUM ISOTOPES
ACTINIDE ISOTOPES
FLUIDS
HYDROGEN COMPOUNDS
ISOTOPES
OXYGEN COMPOUNDS
SEAS
SURFACE WATERS
WATER
520300* - Environment
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