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| Titel |
Lithium isotope systematics of deep-sourced pore fluids at continental margins |
| VerfasserIn |
Florian Scholz, Christian Hensen, Gert J. De Lange, Matthias Haeckel, Volker Liebtrau, Anette Meixner, Anja Reitz, Rolf L. Romer |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250035239
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| Zusammenfassung |
| In the past two decades, the behavior of lithium (Li) isotopes has been studied in various
marine systems, including mid-ocean ridge and sediment-hosted hydrothermal systems,
subduction zone settings and normal coastal and deep-sea sediments recovered by the Ocean
Drilling Program (ODP). Major processes identified to cause deviations from the seawater
isotopic composition are adsorption/desorption reactions, formation and transformation of
silicate minerals, and leaching of Li from sediments or underlying crust at high temperature.
As a result of the accomplished work, Li isotopes are considered a promising tracer for the
diagenetic evolution and provenance of pore fluids in overpressured sedimentary
environments.
Here, we present Li concentration and isotope data of 18 cold seep locations and
reference fluids from shallow marine sediments, a sediment-hosted hydrothermal system and
two Mediterranean brine basins. The new reference data and literature data of hydrothermal
fluids and pore fluids from the ODP follow an empirical relationship reflecting increasing Li
release and decreasing isotope fractionation during clay mineral authigenesis with
increasing temperature. Lithium concentration and isotope data of cold seep fluids are
mostly in agreement with this empirical relationship. Ubiquitous diagenetic signals
of clay dehydration in all cold seep fluids indicate that authigenic smectite-illite
is an important sink for light pore water Li in deeply buried continental margin
sediments. Deviations from the general relationship are attributed to the varying
proportion of weatherable (e.g. volcanogenic) components and to transport-related
fractionation trends. A simple transport-reaction model was applied to simulate Li isotope
fractionation during upwelling of pore fluids to the seafloor. It is demonstrated
that slow pore water advection (order of mm a-1) suffices to convey much of the
deep-seated diagenetic Li signal into shallow sediments. If carefully applied, Li isotope
systematics may, thus, provide a valuable record of fluid/mineral interaction that
has been inherited several hundreds or thousands of meters below the seafloor. |
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