U-Th-Pb systematics in hot springs on the east Pacific rise at 2'/sup 0/N and Guaymas Basin

Journal Article · Sat Nov 01 00:00:00 EST 1986 · Geochim. Cosmochim. Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(86)90030-X· OSTI ID:6896666

Chen, J H; Wasserburg, G J; von Damm, K L; Edmond, J M

The concentrations and isotopic compositions of U, Th and Pb were determined in hydrothermal fluids from 21/sup 0/N, East Pacific Rise and Guaymas Basin, Gulf of California. The purest hydrothermal end members (96%) have 0.06-0.18 ppb U, < 0.1-4.3 ppt Th and 40-67 ppb Pb. Several samples show a /sup 234/U enrichment relative to the equilibrium value. This indicates that U was quantitatively removed from seawater and deposited to the crust during the hydrothermal circulation. The 21/sup 0/N fluids with intermediate Mg content show that U and Mg are coherently removed from seawater, but Pb is not, during mixing of the hot hydrothermal fluid and cold ambient seawater. Both the end-member and intermediate hydrothermal fluids at 21/sup 0/N have similar Pb isotope compositions and limited ranges in /sup 206/Pb//sup 204/Pb (18.444-18.503), /sup 207/Pb//sup 204/Pb (15.471-15.514), and /sup 208/Pb//sup 204/Pb (37l.832-37.966). These ratios are within the range of values of MORB and are distinctly less radiogenic than the ambient seawater. This means that a significant amount of Pb was removed from the basalts by the hot springs. In contrast, Th does not appear to be significantly removed from the basalts. Some of this Pb was incorporated into the metalliferous sediments in a wide area straddling the EPR. The Pb isotopic composition of a hydrothermal sample from the Guaymas Basin is more radiogenic than at 21/sup 0/N and resembles that of sediments from the Gulf of California. This is consistent with the uptake of Pb from heated sediments having a substantial component of the volcanogenic detritus.

• Research Organization: California Institute of Technology, Pasadena
• OSTI ID: 6896666
• Journal Information: Geochim. Cosmochim. Acta; (United States), Vol. 50:11
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
GULF OF CALIFORNIA
HOT SPRINGS
ISOTOPE RATIO
PACIFIC OCEAN
LEAD
LEAD 204
LEAD 206
LEAD 207
LEAD 208
THORIUM
URANIUM
URANIUM 234
ACTINIDE ISOTOPES
ACTINIDE NUCLEI
ACTINIDES
ALPHA DECAY RADIOISOTOPES
ELEMENTS
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
HEAVY NUCLEI
HOURS LIVING RADIOISOTOPES
ISOMERIC TRANSITION ISOTOPES
ISOTOPES
LEAD ISOTOPES
METALS
NUCLEI
RADIOISOTOPES
SEAS
SECONDS LIVING RADIOISOTOPES
STABLE ISOTOPES
SURFACE WATERS
THERMAL SPRINGS
URANIUM ISOTOPES
WATER SPRINGS
YEARS LIVING RADIOISOTOPES
580400* - Geochemistry- (-1989)