Subsolidus reactions in kimberlitic ilmenites: exsolution, reduction and the redox state of the mantle.
Article
Haggerty, SE, Tompkins, LA. (1984). Subsolidus reactions in kimberlitic ilmenites: exsolution, reduction and the redox state of the mantle.
. 335-357. 10.1016/b978-0-444-42273-6.50029-8
Haggerty, SE, Tompkins, LA. (1984). Subsolidus reactions in kimberlitic ilmenites: exsolution, reduction and the redox state of the mantle.
. 335-357. 10.1016/b978-0-444-42273-6.50029-8
Compositions of 13 ilmenite-magnetite pairs in exsolution intergrowths from Koidu, Sierra Leone, and Monastery, South Africa, define an approximate solvus in the ternary system ilmenite-hematite-geikielite. The two sets of data lie on either side of the solvus so that ilmenite from Koidu has produced lamellae enriched in ilmenite-geikielite, and ilmenite from Monastery, lamellae enriched in hematite. These data are consistent with decomposition loops established experimentally at 1300oC and 1 atm. The mineral chemistry of ilmenite-spinel pairs considered to have formed by subsolidus reduction shows coherent trends for Cr-Ti, Fe-Mg and Cr-Mg that permit the T of formation to be determined. These data, coupled with experimental T-fO2 determinations on a Monastery ilmenite, T-fO2 determinations from co-equilibrated oxide pairs and the model mantle fO2 buffer EMOG, allow estimates to be made of the conditions required to initiate reduction.-J.M.H.
