Fe–Ni-rich Silicate Aggregates Formed after Sulfides in High-pressure Serpentinites - INSU - Institut national des sciences de l'Univers
Article Dans Une Revue Journal of Petrology Année : 2017

Fe–Ni-rich Silicate Aggregates Formed after Sulfides in High-pressure Serpentinites

Christian Chopin
Fabrice Brunet
Lucile Bezacier
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Stéphane Guillot

Résumé

High-pressure serpentinites from Alpine Corsica, the Piedmont Zone (Western Alps), the Tso Morari dome (Himalaya), the Dominican Republic and Cuba (Greater Antilles) contain reddish (Ni,Fe)-rich silicate aggregates, a few hundred micrometers in size, which have not been reported so far from lower-pressure serpentinites, nor found there through systematic screening. The high atomic (Ni + Fe)/Si ratio (5 ± 4) of these aggregates, as well as their occurrence as coronas around (Ni,Fe)-sulfides, indicates their formation at the expense of sulfides and serpentine. The high (Ni + Fe)/Si ratio may suggest the presence of an Fe or Ni analogue of the rare serpentine-related minerals balangeroite or cronstedtite. However, compositional variations within and between aggregates, synchrotron X-ray diffraction data acquired on single aggregates, and transmission electron microscopy reveal that these aggregates are not a single phase but rather a mixture at the hundreds of nanometer scale of oxyhydroxides, mainly goethite (FeOOH) + (Ni,Fe)-rich serpentine ± chlorite ± reevesite [Ni6Fe2(OH)16(CO3)·4H2O] ± magnetite. In addition to microtexture and mineralogy, strong chemical variations at the border of the aggregates and along micro-veins suggest formation through a low-temperature alteration process. However, the occurrence of such pseudomorphic aggregates only in high-pressure serpentinites suggests that they were formed at the expense of a high-pressure silicate precursor of high M2+/Si ratio, still to be identified but which could be a main nickel carrier at depth in subduction zones.

Dates et versions

insu-02124390 , version 1 (25-10-2024)

Identifiants

Citer

Benjamin Malvoisin, Christian Chopin, Alain Baronnet, Fabrice Brunet, Lucile Bezacier, et al.. Fe–Ni-rich Silicate Aggregates Formed after Sulfides in High-pressure Serpentinites. Journal of Petrology, 2017, 58 (5), pp.963-978. ⟨10.1093/petrology/egx042⟩. ⟨insu-02124390⟩
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