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Fe-Ti-Zr metasomatism in the oceanic mantle due to extreme differentiation of tholeiitic melts (Moa-Baracoa ophiolite, Cuba)

AuthorsPujol-Solà, Núria; Proenza, Joaquín A.; García-Casco, Antonio; González-Jiménez, J. M.; Román-Alpiste, Manuel Jesús; Garrido, Carlos J. ; Melgarejo, Joan Carles; Gervilla, Fernando ; Llovet, X.
KeywordsOphiolitic chromitites
Zircon coronas
HFSE minerals
Modal metasomatism
Issue Date12-Feb-2020
PublisherElsevier BV
CitationLithos - Amsterdam 358-359: 105420 (2020)
AbstractTi-rich amphibole, Mg-rich ilmenite, baddeleyite, zirconolite, srilankite, and zircon are important high-field-strength elements (HFSE) bearing phases in the Potosí chromitite bodies located in the Moho Transition Zone of the Cretaceous Moa-Baracoa suprasubduction zone ophiolite (eastern Cuba). Such HFSE-bearing phases were found in the interaction zone between gabbroic intrusions and chromitite pods. In addition to HFSE-bearing minerals, the studied samples are composed of Fe and Ti-rich chromite, olivine (Fo), clinopyroxene (En), plagioclase (An), orthopyroxene (En), F-rich apatite, and Fe-Cu-Ni sulfides. The studied ilmenite hosting Zr oxides (baddeleyite, zirconolite, and srilankite) contains up to 13 wt.% MgO. The Potosí zirconolite is the first record of this mineral in ophiolitic chromitites and non-metamorphic ophiolite units, and it has relatively high REE contents (up to 10 wt.% of REEO) and the highest concentrations in YO (up to 11 wt.%) reported so far in zirconolite from terrestrial occurrences. Zircon is observed forming coronas surrounding ilmenite grains in contact with silicate minerals, and is characterized by very low U and Pb contents. The zircons formed after high temperature Zr diffusion in ilmenite (exsolution) and a subsequent reaction along grain boundaries following crystallization. Finally, U-Pb dating of baddeleyite exsolutions within ilmenite yielded an average age of 134.4 ± 14 Ma, which provides the first ever dating for a metasomatic event in Potosí that matches well (within uncertainty) the formation age of the oceanic crust of the eastern Cuba ophiolite. We propose that the occurrence of HFSE- and REE-bearing minerals in the Potosí chromite deposit is the result of a two stage process: first, water-rich and HFSE-rich residual melts are produced by intercumulus crystal fractionation after an evolved MORB (BABB)-like melt; and secondly, these residual melt fractions escaped the solidifying mush and extensively reacted and metasomatized the surrounding chromitites, crystallizing HFSE- and REE-bearing minerals and Fe-Cu-Ni sulfides.
Publisher version (URL)http://dx.doi.org/10.1016/j.lithos.2020.105420
Identifiersdoi: 10.1016/j.lithos.2020.105420
issn: 1872-6143
Appears in Collections:(IACT) Artículos
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