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LUCKYSCALE : Rare Earth element Exchanges at Lucky Strike hydrothermal site

by Webmaster Legos last modified Nov 20, 2020 10:36 AM


Ridge Exchange at Lucky Strike

This work was conducted by Valerie Chavagnac (GET) in collaboration with C. Jeandel (LEGOS)


 Objectives :

Better constraining the REE and Nd isotopic composition of hydrothermal fluids when they are mixed with seawater.


Scientific Rationale

Since the beginning of the GEOTRACES program, our understanding of the role of hydrothermal activity in the trace element oceanic budgets has considerably evolved. For example, hydrothermal plumes are considered now as significant sources of dissolved Fe, what they were not 5 years ago. Similarly, hydrothermal sources have always been considered to be a sink for the rare earth elements (REEs). However, dissolved REE (DREE) observations in hydrothermal plumes are still lacking. Filling this gap is of first importance, REE being efficient oceanic tracers as well as major “high tech” metals. In addition, an earlier study conducted above the East Pacific Rise made us hypothesize that dissolved/particulate exchange could modify the Nd isotopic signature in the vicinity of strong hydrothermal inputs (Jeandel et al, G3, 2013). We wanted to investigate closer this dynamic.



We aimed at better understanding REE behavior at the exit and in the vicinity of a hydrothermal site, once the high-temperature hydrothermal fluids mixed in the deep seawater mass. The selected site is the LUCKY STRIKE hydrothermal field, which is the location of the deep sea observatory (EMSO-Azores). The originality of our study is in the in-situ filtration of hydrothermal samples using the IFREMER PEPITO device (Figure below), limiting therefore chemical exchange between particle and dissolved element. Meanwhile, we measured for the first time, the Nd isotopic signatures of buoyant
hydrothermal plume fluids.


Results & perspective


REE concentrations
We find that 27 to 62% of total hydrothermal DREEs are rapidly scavenged by anhydrite precipitation at the onset of buoyant plume formation. This result is challenging the preceding hypothesis suggesting that Fe and Mn oxides were the main REE carriers (Figure 1)


Nd isotope signatures
The four LSHF black smoker fluids record and preserve the DNd isotope signatures of the substratum, i.e. DNd at +7.8 to +9.0
This work showed that dissolved Nd signature (DεNd) in the evolving plume are identical to black smoker DεNd of +9.0 and contrast radically with DεNd of the local deep water mass at -12.0. Plume DεNd as low as +6.6 may be reconciled by dissolution of newly formed barite in the local environment and carrying seawater DεNd signature.



Catherine Jeandel and Valerie Chavagnac are participating to the HERMINE project. Samples were collected for REE, Nd isotopes, Sr and Li isotopes in the TAG plume and hydrothermal plume as part of the last HERMINE cruise (2017). Analyses are planned for 2019.


Master 2: Saleban Ali Hassan (2016) co-ecadré CJ et VC
Publications: Chavagnac V., Saleban Ali H., Jeandel C., Leleu T., Destrigneville C., Castillo A., Cotte L., Waeles M., Cathalot C., Haes-Huon A., Nonnotte P., Sarradin P.-M., Cannat M., 2018. Sulfate minerals control dissolved rare earth element flux and Nd isotope signature of buoyant hydrothermal plume (EMSO-Azores, 37ºN Mid-Atlantic Ridge). Chemical Geology, doi: 10.1016/j.chemgeo.2018.09.021



Catherine Jeandel (CNRS, TIM), Valérie Chavagnac (CNRS, GET), Hassan Saleban Ali (M2 GET-LEGOS), Thomas Leleu (Doc, GET), Moustafa Belhadj (CNRS, TIM)





French ANR LuckyScales project (ANR-14-CE02-0008) and the EU EMSO project
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