FN Archimer Export Format
PT J
TI Coupled Ge/Si and Ge isotope ratios as geochemical tracers of seafloor hydrothermal systems: Case studies at Loihi Seamount and East Pacific Rise 9°50’N
BT 
AF ESCOUBE, Raphaelle
   ROUXEL, Olivier
   EDWARDS, Katrina
   GLAZER, Brian
   DONARD, Olivier F. X.
AS 1:1,2,3;2:2,4;3:5;4:6;5:1;
FF 1:;2:PDG-REM-GM-LGM;3:;4:;5:;
C1 Univ Pau & Pays Adour, LCABIE, CNRS UMR 525, F-64053 Pau, France.
   Univ Bretagne Occidentale, Inst Europeen Univ Mer, Plouzane, France.
   Univ Oxford, Dept Earth Sci, Oxford OX1 3PR, England.
   IFREMER, Ctr Brest, Plouzane, France.
   Univ So Calif, Los Angeles, CA 90089 USA.
   Univ Hawaii, Dept Oceanog, Honolulu, HI 96822 USA.
C2 UNIV PAU & PAYS ADOUR, FRANCE
   UBO, FRANCE
   UNIV OXFORD, UK
   IFREMER, FRANCE
   UNIV CALIF LOS ANGELES, USA
   UNIV HAWAII, USA
SI BREST
SE PDG-REM-GM-LGM
IN WOS Ifremer jusqu'en 2018
   copubli-france
   copubli-europe
   copubli-univ-france
   copubli-int-hors-europe
IF 4.315
TC 34
UR https://archimer.ifremer.fr/doc/00273/38403/36728.pdf
LA English
DT Article
AB Germanium (Ge) and Silicon (Si) exhibit similar geochemical behaviour in marine environments but are variably enriched in seafloor hydrothermal fluids relative to seawater. In this study, Ge isotope and Ge/Si ratio systematics were investigated in low temperature hydrothermal vents from Loihi Seamount (Pacific Ocean, 18°54’N, 155°15’W) and results were compared to high-temperature vents from the East Pacific Rise (EPR) at 9°50’N. Loihi offers the opportunity to understand contrasting Ge and Si behaviour in low temperature seafloor hydrothermal systems characterized by abundant Fe oxyhydroxide deposition at the seafloor. The results show that both Ge/Si and δ74/70Ge in hydrothermal fluids are fractionated relative to the basaltic host rocks. The enrichment in Ge vs. Si relative to fresh basalts, together with Ge isotope fractionation (Δ74/70Ge fluid-basalt up to 1.15 ‰ at EPR 9°50’N and 1.64 ‰ at Loihi) are best explained by the precipitation of minerals (e.g. quartz and Fe-sulfides) during higher temperature seawater-rock reactions in the subsurface. The study of Fe-rich hydrothermal deposits at Loihi, largely composed of Fe-oxyhydroxides, shows that Ge isotopes are also fractionated upon mineral precipitation at the seafloor. We obtained an average Ge isotope fractionation factor between Fe-oxyhydroxide (ferrihydrite) and dissolved Ge in the fluid of -2.0 ± 0.6 ‰ (2sd), and a maximum value of -3.6 ± 0.6 ‰ (2sd), which is consistent with recent theoretical and experimental studies. The study of a hydrothermal chimney at Bio 9 vent at EPR 9°50’N also demonstrates that Ge isotopes are fractionated by approximately -5.6 ± 0.6 ‰ (2sd) during precipitation of metal sulfides under hydrothermal conditions. Using combined Ge/Si and estimated Ge isotope signatures of Ge sinks and sources in seawater, we propose a preliminary oceanic budget of Ge which reveals that an important sink, referred as the “missing Ge sink”, may correspond to Ge sequestration into authigenic Fe-oxyhydroxides in marine sediments. This study shows that combining Ge/Si and δ74/70Ge systematics provides a useful tool to trace hydrothermal Ge and Si sources in marine environments and to understand formation processes of seafloor hydrothermal deposits.
PY 2015
PD OCT
SO Geochimica Et Cosmochimica Acta
SN 0016-7037
PU Pergamon-elsevier Science Ltd
VL 167
UT 000361007300006
BP 93
EP 112
DI 10.1016/j.gca.2015.06.025
ID 38403
ER

EF