Skip to content. | Skip to navigation

Laboratoire d’Etudes en Géophysique et Océanographie Spatiales

Personal tools

This is SunRain Plone Theme

Navigation

You are here: Home / Equipes de Recherche / TIM / Projects / LUCKYSCALE

LUCKYSCALE

by Webmaster Legos last modified Nov 21, 2019 09:10 PM

Published by François Lacan, November 2019

 

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.

 

Strategy


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.

 

Future:

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.


Indicators:

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

 

Participants

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


Partners:

GET, LEMAR, LGO, IFREMER (LEP, LGC, LDCO), IPGP,

 

Funding:

French ANR LuckyScales project (ANR-14-CE02-0008) and the EU EMSO project
667 (http://www.emso-eu.org).



Document Actions