Al-free di-trioctahedral substitution in chlorite and a ferri-sudoite end-member

Vincent Trincal (1) , Pierre Lanari (2)

1 LCE - Laboratoire Chrono-environnement (UMR 6249)
2 Institute of Geological Sciences [Bern]

A compilation of Fe 3+-bearing chlorite analyses is used: (1) to investigate the Al-free di-trioctahedral (AFDT) substitution 2Fe 3+ + □ = 3(Mg,Fe 2+) in chlorite; and (2) to estimate the composition of a ferri-sudoite end-member (Si 3 Al)[(Fe 2+ ,Mg) 2 Fe 3+ 2 □Al]O 10 (OH) 8 within the chlorite solid-solution domain. According to our observations, up to two Fe 3+ cations might be allocated in the M2-M3 chlorite sites by the substitution AFDT, which does not involve Al. These unexpected observations were made possible by the development of µXANES techniques allowing in situ measurements of XFe 3+ (Fe 3+ /(Fe 2+ + Fe 3+)) in heterogeneous chlorite. Although further studies are required to confirm the crystallographic position of Fe 3+ and refine its ionic/ magnetic behaviour in chlorite, this development creates opportunities for developing new geothermometers.

Mots clés: sudoite; chlorite; μXANES; geothermometry

Domaines: Géochimie

Vincent Trincal, Pierre Lanari. Al-free di-trioctahedral substitution in chlorite and a ferri-sudoite end-member. Clay Minerals, 2016, 51 (4), pp.675-689. ⟨10.1180/claymin.2016.051.4.09⟩. ⟨hal-01502795⟩