The scavenging of U, sup 230 Th and sup 231 Pa during pulsed hydrothermal activity at 20 degree S, East Pacific Rise

Journal Article · Tue Mar 01 04:00:00 EST 1988 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(88)90329-8· OSTI ID:5231351

Shimmield, G B; Price, N B ^[1]

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1. Univ. of Edinburgh (Scotland)

Uranium, Th and Pa isotopes were measured in eight box-cores from two transects to the west of the East Pacific Rise at 10{degree}S and 20{degree}S. Sediment geochemistry (Al, Ca, Fe, Mn) and water column particulates (Mn) suggest that highly metalliferous plumes, rich in Fe and Mn, are emanating from the rise crest at 19{degree}S. Measurements of {sup 230}Th{sub xs} and {sup 231}Pa{sub xs} indicate decreasing sediment accumulation rates from the rise flank (0.4 cm ky{sup {minus}1}) to the Tiki Basin (0.23 cm ky{sup {minus}1}). Over this geographical area Al is found to have a constant flux of 3.6 {times} 10{sup {minus}4} g cm{sup {minus}2} ky{sup {minus}1}. Application of an Al constant flux model to ridge crest metalliferous sediment reveals two 1,000 year pluses of hydrothermal activity during the Holocene (since 11,000 y BP). These hydrothermal pulses are characterized by hydrothermal Fe/Mn ratios (3.5:1), enhanced {sup 230}Th and {sup 231}Pa scavenging, and low {sup 230}Th{sub xs}/{sup 231}Pa{sub xs} ratios (3-4). The similarity of the {sup 230}Th{sub xs}/{sup 231}Pa{sub xs} ratio to the dissolved seawater ratio suggests that no fractionation of the isotopes occurs during scavenging. Supplementary supply of dissolved {sup 230}Th and {sup 231}Pa in a westwards-moving water mass is suggested.

• OSTI ID: 5231351
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Journal Name: Geochimica et Cosmochimica Acta; (USA) Vol. 52:3; ISSN GCACA; ISSN 0016-7037
• Country of Publication: United States
• Language: English

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