Cited by 43Geological and Geochemical AnalysisGeochemistry and Elemental AnalysisPaleontology and Stratigraphy of Fossils

Multiple Stages of Carbonation and Element Redistribution during Formation of Ultramafic-Hosted Magnesite in Neoproterozoic Ophiolites of the Arabian-Nubian Shield, Egypt

Azer, Mokhles K., Gahlan, Hisham A., Asimow, Paul D., Mubarak, Heba S., Al-Kahtany, Khaled M.·2019·The Journal of Geology

Abstract

We present a study of the serpentinized peridotites of the Ghadir-Mohagar-Ambaut area, Egypt. They represent the mantle section of a dismembered ophiolite, tectonically emplaced over a volcanosedimentary succession of island arc assemblages. The serpentinites are variably metamorphosed from greenschist to lower-amphibolite facies, metasomatized, and altered, including development of talc-carbonate and quartz-carbonate rocks, especially along shear zones and fault planes. Nevertheless, some samples contain relics of primary chromian spinel, olivine, and pyroxenes. Relict textures and whole-rock compositions (Mg#[molar Mg/(Mg+Fe2+)]=0.92–0.93, with low Al2O3 and CaO contents) both suggest harzburgite protoliths. The high Mg# and Ni contents of relict olivine and the high Cr# (molar Cr/(Cr+Al)) of fresh chromian spinel cores indicate that the protoliths experienced high degrees of partial melt extraction (∼34%–39%), well beyond the limit for exhaustion of clinopyroxene from the residue and consistent with formation in a forearc suprasubduction zone environment. The serpentinized ultramafic rocks in the study area are divided into massive serpentinite, serpentinite-hosted magnesite masses, and magnesite-filled veins. The carbonation and formation of magnesite ores took place through two metasomatic stages; the first is represented by the magnesite masses and associated with deep-seated metasomatism and alteration during serpentinization, whereas the second, vein-forming stage postdates serpentinization and occurred during obduction of the ophiolite. The differences in chemical composition between massive serpentinite and serpentinite-hosted magnesite masses suggest leaching of some elements and enrichment of others during carbonation; MgO, Cr, and Ni are depleted, whereas Fe2O3, CaO, MnO, Nb, Ba, Cu, Pb, Sr, and Zn are enriched in the serpentinite-hosted magnesite masses, relative to the host massive serpentinite.

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Crossref · 10.1086/700652

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  • Natural carbon uptake in ultramafic formations is significant as evidenced by abundantly exposed carbonate-bearing ophiolite complexes worldwide.

    “Natural carbon uptake in ultramafic formations is significant as evidenced by abundantly exposed carbonate-bearing ophiolite complexes worldwide (Akbulut et al., 2006; Azer et al., 2019; Barnes & O'Neil, 1969; Barnes et al., 1978; Beinlich et al., 2010, 2012, 2018, 2020a; Belogub et al., 2017; Emam & Zoheir, 2013; Gahlan Hisham et al., 2018; García del Real et al., 2016; H”

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Authors
Azer, M. K., Gahlan, H. A., Asimow, P. D., Mubarak, H. S., & Al-Kahtany, K. M.
Affiliations
  • National Research Centre (EG)
  • King Saud University (SA)
  • California Institute of Technology (US)
Corresponding author
  • Azer, Mokhles K.
  • Gahlan, Hisham A.
  • Asimow, Paul D.
  • Mubarak, Heba S.
  • Al-Kahtany, Khaled M.
Venue
The Journal of Geology
Published
2019-01
Volume
127
Issue
1
Pages
81-107
ISSN
  • 0022-1376 (ISSN-L)
  • 1537-5269
OpenAlex
W2905178961
Cited by
43
References
109
Citations by year
2026: 2 · 2025: 3 · 2024: 8 · 2023: 5 · 2022: 4 · 2021: 7 · 2020: 9 · 2019: 5
FWCI
3.77
Type
journal article
Language
en
Open access
closed
Locations
  • The Journal of Geology (publishedVersion)
  • CaltechAUTHORS (California Institute of Technology) (submittedVersion)
Topics
  • Physical Sciences › Earth and Planetary Sciences › Geophysics › Geological and Geochemical Analysis
  • Physical Sciences › Earth and Planetary Sciences › Geochemistry and Petrology › Geochemistry and Elemental Analysis
  • Physical Sciences › Earth and Planetary Sciences › Paleontology › Paleontology and Stratigraphy of Fossils
Keywords
magnesite, serpentinization, peridotite, ultramafic rocks, ophiolite, metasomatism, carbonation, element redistribution, supra-subduction zone, obduction, Arabian-Nubian Shield, Neoproterozoic, chromian spinel

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