Carbonate-orthopyroxenite lenses from the Neoproterozoic Gerf ophiolite, South Eastern Desert, Egypt: The first record in the Arabian Nubian Shield ophiolites

Gahlan, Hisham A.; Arai, Shoji

doi:10.1016/j.jafrearsci.2008.09.005

Cited by 18 publications

(3 citation statements)

References 60 publications

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“…9 a Mg# vs. NiO (wt.%) of olivine (ol) from the Abu Dahr serpentinized peridotites, field of mantle olivine array is adopted from Takahashi (1987), fields of olivines from ophiolites (Khalil and Azer 2007) and layered intrusions (Helmy and Mahallawi 2003;Abd ElRahman et al 2012), are all given for comparison. b Mg# vs. Cr 2 O 3 (wt.%) of orthopyroxene (opx) from the Abu Dahr serpentinized harzburgite, field of metamorphic opx is from Gahlan and Arai (2009), and field of primary opx from depleted harzburgite is after Kubo (2002) and Ishimaru et al (2007). c CaO vs. Al 2 O 3 (wt.%) of orthopyroxene (opx) from the Abu Dahr serpentinized harzburgite.…”

Section: Crustal Section (Mafic Rocks)mentioning

confidence: 99%

The Neoproterozoic Abu Dahr ophiolite, South Eastern Desert, Egypt: petrological characteristics and tectonomagmatic evolution

2015

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The Neoproterozoic Abu Dahr ophiolite, South Eastern Desert, Egypt, is one of the best preserved and least dismembered ophiolite successions in the Arabian-Nubian Shield. It contains a Penrose-type ophiolite sequence from mantle section below mafic crust upward to oceanic sedimentary cover overlying mafic volcanics, although the original magmatic (stratigraphic) contact between the mantle and crustal sections is disrupted by tectonism. The Abu Dahr ophiolite is metamorphosed under greenschist facies conditions, and low-temperature alteration is widespread. Petrography reveals that: (i) the mantle is homogenous, serpentinized, and dominated by harzburgite and less abundant dunite; (ii) the cumulate ultramafics are represented by wehrlite and pyroxenite; and (iii) the crustal section is represented by metagabbros, meta-anorthosites and metabasalts. The Abu Dahr serpentinized peridotites show high Mg# (0.92-0.93), with enrichment of Ni, Cr and Co, and depletion of Al 2 O 3 and CaO, and nearly flat and unfractionated REE chondrite-normalized pattern. Major and trace element characteristics of the Abu Dahr metagabbro and metabasalt (crustal section) indicate a tholeiitic to calc-alkaline affinity. Units of the crustal section have low-Nb and Zr concentrations, low Dy/Yb and relatively elevated La/Yb ratios, high U/Yb and Th/Yb ratios, and LREE enriched chondrite-normalized pattern. All of the Abu Dahr ophiolite units have trace-element signatures characterized by enrichment of LILE over HFSE. Rare and trace element patterns indicate a genetic link between the Abu Dahr mantle, cumulate ultramafics, and crust. Chromian spinel has survived metamorphism and is used as a petrogenetic indicator in the Abu Dahr serpentinized peridotites. The spinel is homogeneous with a limited composition, and shows high-Cr# (>0.6) combined with low-TiO 2 character (mostly <0.1 wt.%). The Abu Dahr ophiolite is interpreted as a fragment of depleted oceanic lithosphere that experienced high degrees of partial melting (up to 35 %) and originated in a fore-arc setting. Such interpretation contributes to the body of evidence suggesting that tectonomagmatic processes of the Neoproterozoic were largely similar to those of the Phanerozoic, implying little, or no significant, change in the geothermal regime of Earth since the Neoproterozoic.

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Section: Crustal Section (Mafic Rocks)mentioning

confidence: 99%

The Neoproterozoic Abu Dahr ophiolite, South Eastern Desert, Egypt: petrological characteristics and tectonomagmatic evolution

2015

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“…Olivine with similar characteristics has been reported in serpentinized peridotites from other ANS ophiolites and labeled metamorphic olivine (e.g., Khalil and Azer, 2007;Ali et al, 2020).Metamorphic olivine in various ANS serpentinites has been attributed either to thermal effects of granitoid intrusions (e.g. Gahlan and Arai, 2009;Khalil and Azer, J o u r n a l P r e -p r o o f Journal Pre-proof 2007;Ali et al, 2020) or to low-pressure high-temperature regional metamorphism (Gahlan et al, 2015. In the current case, sample 53 is the only sample with metamorphic olivine and was collected close to the contact with a younger granodiorite intrusion, so this is evidently a case of contact metamorphism.…”

Section: Formation Of Metamorphic Olivine In Serpentinitementioning

confidence: 58%

Mineralogical and geochemical study of rodingites and associated serpentinized peridotite, Eastern Desert of Egypt, Arabian-Nubian Shield

Mubarak

Azer

Surour

et al. 2020

Lithos

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This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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“…Orthopyroxenites have been hardly reported in the ophiolite complexes of the EDE. They are only recorded in Kurbiyay, Hammariya, Bir Al-Edeid, Mudarjaj and Gerf ophiolite complexes (Abdel-Karim et al, 2008Ahmed et al, 2012;Azer and Khalil, 2005;Gahlan and Arai, 2009). The origin of the orthopyroxenites in Mudarjaj ophiolite complex in the SED of Egypt was attributed to contamination of their arc-related melts by crustal rocks (Ahmed et al, 2012).…”

Section: Origin Of the Orthopyroxenitementioning

confidence: 99%

Origin and evolution of Neoproterozoic metaophiolitic mantle rocks from the eastern Desert of Egypt: Implications for tectonic and metamorphic events in the Arabian-Nubian Shield

Ali

Azer²,

Abdel‐Karim³

2023

GeA

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The mantle rocks from Kadaboura and Madara areas represent sections of dismembered ophiolitic complexes developed during the Neoproterozoic in the Eastern Desert of Egypt, which is located in the northwestern corner of the Arabian–Nubian Shield. The Kadaboura mantle rocks comprise serpentinites and serpentinized dunites, whereas those of the Madara consist of serpentinites and serpentinized pyroxenites.Despite the serpentinization of the studied mantle rocks, few relicts of primary chromite, olivine and pyroxene are preserved. Chromite is partly altered having unaltered Al-rich chromite cores surrounded by Fe-rich chromite and Cr-rich magnetite rims. The unaltered Al-rich chromite cores show compositions equilibrated at temperatures mostly below ~500-600°C, which is a temperature comparable to that estimated for primary chromite in greenschist up to lower amphibolite facies rocks. The high Cr# [100×Cr/(Cr+Al)= 47-76] of the unaltered chromite cores and the Mg-rich nature of the olivine relicts (Fo91–94) indicate that the studied mantle rocks were produced from a highly depleted mantle that experienced high degrees of melt extraction (mostly ~30-40%). This range of melt extraction resembles that estimated for supra-subduction zone peridotites, but higher than that in abyssal and passive margin peridotites. Furthermore, the clinopyroxene relicts show compositions comparable to those from the Mariana forearc peridotites. Bulk-rock geochemistry also reflects derivation from an extremely depleted and a highly refractory mantle source. Modelling of rare-earth elements suggests that the studied mantle rocks were possibly formed by the interaction of their highly depleted harzburgitic mantle precursors with subduction-related melts/fluids during their evolution in a fore-arc basin of the supra-subduction zone.The proposed geodynamic model suggests that the oceanic lithosphere generated during the seafloor spreading of the Mozambique Ocean was emplaced in the upper plate of the intra-oceanic subduction zone, in which the formely depleted Neoproterozoic mantle of the Arabian-Nubian Shield experienced mature phases of hydrous melting, extreme depletion and enrichment.

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Carbonate-orthopyroxenite lenses from the Neoproterozoic Gerf ophiolite, South Eastern Desert, Egypt: The first record in the Arabian Nubian Shield ophiolites

Cited by 18 publications

References 60 publications

The Neoproterozoic Abu Dahr ophiolite, South Eastern Desert, Egypt: petrological characteristics and tectonomagmatic evolution

The Neoproterozoic Abu Dahr ophiolite, South Eastern Desert, Egypt: petrological characteristics and tectonomagmatic evolution

Mineralogical and geochemical study of rodingites and associated serpentinized peridotite, Eastern Desert of Egypt, Arabian-Nubian Shield

Origin and evolution of Neoproterozoic metaophiolitic mantle rocks from the eastern Desert of Egypt: Implications for tectonic and metamorphic events in the Arabian-Nubian Shield

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