科研之友
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摘要
We present measurements of Ge isotope composition and ancillary data for samples of river water, low- and high-temperature hydrothermal fluids, and seawater. The dissolved delta Ge-74 composition of analyzed rivers ranges from 2.0 to 5.6 parts per thousand, which is significantly heavier than previously determined values for silicate rocks (delta Ge-74 = 0.4-0.7 parts per thousand, Escoube et al., Geostand. Geoanal. Res., 36(2), 2012) from which dissolved Ge is primarily derived. An observed negative correlation between riverine Ge/Si and delta Ge-74 signatures suggests that the primary delta Ge-74 fractionation mechanism during rock weathering is the preferential incorporation of light isotopes into secondary weathering products. High temperature (> 150 degrees C) hydrothermal fluids analyzed in this study have delta Ge-74 of 0.7-1.6 parts per thousand, most likely fractionated during fluid equilibration with quartz in the reaction zone. Low temperature (25-63 degrees C) hydrothermal fluids are heavier (delta Ge-74 between 2.9 parts per thousand and 4.1 parts per thousand) and most likely fractionated during Ge precipitation with hydrothermal clays. Seawater from the open ocean has a delta Ge-74(sw) value of 3.2 +/- 0.4 parts per thousand, and is indistinguishable among the different ocean basins at the current level of precision. This value should be regulated over time by the isotopic balance of Ge sources and sinks, and a new compilation of these fluxes is presented, along with their estimated isotopic compositions. Assuming steady-state, non-opal Ge sequestration during sediment authigenesis likely involves isotopic fractionation (DGesolid-solution)-Ge-74 that is -0.6 +/- 1.8 parts per thousand.
- 出版日期2017-4-15
