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The chromitites of the Neoproterozoic Bou Azzer ophiolite (central Anti-Atlas, Morocco) revisited

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doi: 10.1016/j.oregeorev.2021.104166
Authors:Pujol-Solà, Núria; Dominguez-Carretero, Diego; Proenza, Joaquin A.; Haissen, Faouziya; Ikenne, Moha; González-Jiménez, José Maria; Colás, Vanessa; Maacha, Lhou; Garcia-Casco, Antonio
Author Affiliations:Primary:
Universitat de Barcelona, Facultat de Ciències de la Terra, Departament de Mineralogia, Petrologia i Geologia Aplicada, Barcelona, Spain
Other:
Université Hassan II, Faculté des Sciences Ben M'sik, LGAGE, Département de Géologie, Morocco
Ibn Zohr University, Faculty of Sciences, LAGAGE, Agadir, Morocco
Universidad de Granada, Facultad de Ciencias, Departamento de Mineralogia y Petrologia, Granada, Spain
Instituto Andaluz de Ciencias de la Tierra (CSIC-UGR), Granada, Spain
Universidad Nacional Autónoma de México, Instituto de Geologia, Ciudad de, Mexico
MANAGEM Group, Casablanca, Morocco
Volume Title:Ore Geology Reviews
Source:Ore Geology Reviews, Vol.134. Publisher: Elsevier, Amsterdam, International. ISSN: 0169-1368
Publication Date:2021
Note:In English
Summary: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.
Record ID:902630-42
Copyright Information:GeoRef, Copyright 2021 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands
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