The chromitites of the Neoproterozoic Bou Azzer ophiolite (central Anti-Atlas, Morocco) revisited
Por:
Pujol-Sola, Nuria, Dominguez-Carretero, Diego, Proenza, Joaquin A., Haissen, Faouziya, Ikenne, Moha, Gonzalez-Jimenez, Jose Maria, Colas, Vanessa, Maacha, Lhou, Garcia-Casco, Antonio
Publicada:
1 ene 2021
Resumen:
The Neoproterozoic Bou Azzer ophiolite in the Moroccan Anti-Atlas Panafrican belt hosts numerous chromitite orebodies within the peridotite section of the oceanic mantle. The chromitites are strongly affected by serpentinization and metamorphism, although they still preserve igneous relicts amenable for petrogenetic interpretation. The major, minor and trace element composition of unaltered chromite cores reveal two compositional groups: intermediate-Cr (Cr# = 0.60 – 0.74) and high-Cr (Cr# = 0.79 – 0.84) and estimates of parental melt compositions suggest crystallization from pulses of fore-arc basalts (FAB) and boninitic melts, respectively, that infiltrated the oceanic supra-subduction zone (SSZ) mantle. A platinum group elements (PGE) mineralization dominated by Ir-Ru-Os is recognized in the chromitites, which has its mineralogical expression in abundant inclusions of Os-Ir alloys and coexisting magmatic laurite (RuS2) and their products of metamorphic alteration. Unusual mineral phases in chromite, not previously reported in this ophiolite, include super-reduced and/or nominally ultra-high pressure minerals moissanite (SiC), native Cu and silicates (oriented clinopyroxene lamellae), but “exotic” zircon and diaspore have also been identified. We interpret that clinopyroxene lamellae have a magmatic origin, whereas super-reduced phases originated during serpentinization processes and diaspore is linked to late circulation of low-silica fluids related to rodingitization. Zircon grains, on the other hand, with apatite and serpentine inclusions, could either have formed after the interaction of chromitite with mantle-derived melts or could represent subducted detrital sediments later incorporated into the chromitites. We offer a comparison of the Bou Azzer chromitites with other Precambrian ophiolitic chromitites worldwide, which are rather scarce in the geological record. The studied chromitites are very similar to the Neoproterozoic chromitites reported in the Arabian-Nubian shield, which are also related to the Panafrican orogeny. Thus, we conclude that the Bou Azzer chromitites formed in a subduction-initiation geodynamic setting with two-stages of evolution, with formation of FAB-derived intermediate-Cr chromitites in the early stage and formation of boninite-derived high-Cr chromitites in the late stage. © 2021 Elsevier B.V.
Filiaciones:
Pujol-Sola, Nuria:
Departament de Mineralogia, Petrologia i Geologia Aplicada, Facultat de Ciències de la Terra, Universitat de Barcelona, Carrer Martí i Franquès, s/n, Barcelona, 08028, Spain
Univ Barcelona, Fac Ciencies Terra, Dept Mineral Petr & Geol Aplicada, Carrer Marti Franques S-N, Barcelona 08028, Spain
Dominguez-Carretero, Diego:
Departament de Mineralogia, Petrologia i Geologia Aplicada, Facultat de Ciències de la Terra, Universitat de Barcelona, Carrer Martí i Franquès, s/n, Barcelona, 08028, Spain
Univ Barcelona, Fac Ciencies Terra, Dept Mineral Petr & Geol Aplicada, Carrer Marti Franques S-N, Barcelona 08028, Spain
Proenza, Joaquin A.:
Departament de Mineralogia, Petrologia i Geologia Aplicada, Facultat de Ciències de la Terra, Universitat de Barcelona, Carrer Martí i Franquès, s/n, Barcelona, 08028, Spain
Univ Barcelona, Fac Ciencies Terra, Dept Mineral Petr & Geol Aplicada, Carrer Marti Franques S-N, Barcelona 08028, Spain
Haissen, Faouziya:
LGAGE, Département de Géologie, Faculté des Sciences Ben M'sik, Université Hassan II, Morocco
Univ Hassan 2, Fac Sci Ben Msik, LGAGE, Dept Geol, Casablanca, Morocco
Ikenne, Moha:
LAGAGE, Faculty of Sciences, Ibn Zohr University, Agadir, Morocco
Ibn Zohr Univ, LAGAGE, Fac Sci, Agadir, Morocco
Gonzalez-Jimenez, Jose Maria:
Departamento de Mineralogía y Petrología, Facultad de Ciencias, Universidad de Granada, Avda. Fuentenueva, s/n, Granada, 18071, Spain
Instituto Andaluz de Ciencias de la Tierra (CSIC-UGR), Avda. de las Palmeras 4, E-18100 Armilla, Granada, Spain
Univ Granada, Fac Ciencias, Dept Mineral & Petr, Avda Fuentenueva S-N, Granada 18071, Spain
Univ Nacl Autonoma Mexico, Inst Geol, Ciudad Univ, E-18100 Granada, Spain
Colas, Vanessa:
Instituto de Geología, Universidad Nacional Autónoma de México, Ciudad Universitaria, Ciudad de México, 04510, Mexico
MANAGEM Grp, 191 Bd Mohamed Zerktouni, A-20100 Casablanca, Morocco
Maacha, Lhou:
MANAGEM Group, 191, bd Mohamed Zerktouni, angle bd., Massira Alkhadra, Twin Center Tour, Casablanca, A-20100, Morocco
Garcia-Casco, Antonio:
Departamento de Mineralogía y Petrología, Facultad de Ciencias, Universidad de Granada, Avda. Fuentenueva, s/n, Granada, 18071, Spain
Instituto Andaluz de Ciencias de la Tierra (CSIC-UGR), Avda. de las Palmeras 4, E-18100 Armilla, Granada, Spain
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