The alkali element and boron geochemistry of the Escanaba Trough sediment-hosted hydrothermal system

被引:57
作者
James, RH
Rudnicki, MD
Palmer, MR
机构
[1] Univ Bristol, Dept Earth Sci, Bristol BS8 1RJ, Avon, England
[2] Univ Cambridge, Dept Earth Sci, Cambridge CB2 3EQ, England
[3] Univ London Imperial Coll Sci Technol & Med, TH Huxley Sch, London SW7 2BP, England
关键词
alkali metals; boron; geochemistry; geothermal systems; Escanaba Trough;
D O I
10.1016/S0012-821X(99)00140-5
中图分类号
P3 [地球物理学]; P59 [地球化学];
学科分类号
0708 ; 070902 ;
摘要
A suite of conjugate pore fluid and sediment samples were collected during Leg 169 of the ODP from within the elastic sedimentary sequences which host massive sulphides at Central Hill, Escanaba Trough (ODP Site 1038). We report the alkali element and boron, and Li and B isotope data for these samples. Relative to a reference site (Site 1037) located outside the zone of high heat flow, pore fluids from Site 1038; show a wide variation in Cl (300-800 mM), and have far higher concentrations of Li (up to 6.2 mM), B (up to 9.7 mM), Ca (up to 5.0 mu M), and Rb (up to 97 mu M). We show that the pore fluids are derived from hydrothermal circulation that has extended into the basement oceanic crust, with input of the alkali elements and B as the rising hydrothermal fluids interact geochemically with the overlying elastic sediments. There is, however, no marked depletion of these elements in the conjugate sediments, suggesting that. there has been advective transport of fluids away from the primary hydrothermal reaction site. This is supported by modelling of the Li and B isotope systematics of the pore fluids, which shows that they record extensive formation of secondary minerals during cooling of the fluids from similar to 350 to similar to 20 degrees C. Precipitation of metal-rich sulphides would have occurred prior to the formation of these minerals, thus, the pore fluid Li and B isotope data can place important constraints on the locus of sulphide deposition beneath the seafloor at Escanaba. (C) 1999 Elsevier Science B.V. All rights reserved.
引用
收藏
页码:157 / 169
页数:13
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