Supra-subduction affinity in the Neoproterozoic serpentinites in the Eastern Desert, Egypt: Evidence from mineral composition

Khalil, Ahmed E.; Azer, Mokhles K.

doi:10.1016/j.jafrearsci.2007.08.002

Cited by 75 publications

(37 citation statements)

References 50 publications

(74 reference statements)

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“…6d). Such a setting for the ophiolitic rocks in the Eastern Desert is supported by the fact that clinopyroxene and olivine compositions of most Egyptian ophiolites plot in the field characteristic of intraoceanic fore-arc regions (Abdel Aal et al 2003;Khalil and Azer 2007). Also, the boninitic affinities of some Eastern Desert ophiolitic rocks support a fore-arc setting (e.g.…”

Section: Tectonic Setting and Petrogenesismentioning

confidence: 95%

“…El Sayed et al 1999;Farahat et al 2004;Abd El-Rahman et al 2009;Basta et al 2011). A fore-arc setting has rarely been considered for the ophiolites (Azer and Stern 2007;Khalil and Azer 2007;Abd El-Rahman et al 2009;Hamdy et al 2013;Khedr and Arai 2013;Azer et al 2013).…”

Section: Tectonic Setting and Petrogenesismentioning

confidence: 99%

“…These two secondary phases are usually attributed to the effects of low to medium grade metamorphism up to lower amphibolite facies (Thalhammer et al 1990;McElduff and Stumpfl 1991). In Egyptian ophiolites, the alteration of chromian spinels to ferritchromite may have started during the late magmatic stage but it is mainly due to the much later serpentinization and tectonism (Khudeir et al 1992;Khalil and Azer 2007). Farahat (2008) attributed the formation of chromian spinel cores followed by ferritchromite and Cr-magnetite rims to formation at transitional greenschist-amphibolite to lower amphibolite facies.…”

Section: Alteration Of Chromian Spinelmentioning

confidence: 99%

“…The chromian spinels of ANS ophiolite ultramafic rocks display zoning from fresh chromian spinel cores to ferritchromite and Cr-magnetite rims (e.g. Khalil and Azer 2007;Farahat 2008;Ahmed et al 2012;Khedr and Arai 2013). On the other hand, the chromian spinels of ultramafics in the mafic-ultramafic layered intrusions are not zoned (e.g.…”

Section: Correlations With Other Late Neoproterozoic Ultramafic Rocksmentioning

confidence: 99%

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Petrological studies of neoproterozoic serpentinized ultramafics of the nubian shield: spinel compositions as evidence of the tectonic evolution of egyptian ophiolites

Azer¹

2014

Acta Geologica Polonica

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The mafic-ultramafic rocks of the Gabal El-Degheimi area, Central Eastern Desert of Egypt, are parts of an ophiolitic section. The ophiolitic rocks are dismembered and tectonically enclosed within, or thrust over, island arc assemblages. Serpentinites, altered slices of the upper mantle, represent a distinctive lithology of the dismembered ophiolites. Some portions of the serpentinized rocks contain fresh relicts of primary minerals such as chromian spinel and olivine. The abundance of bastite and mesh textures suggests harzburgite and dunite protoliths, respectively, for these serpentinites. Some fresh cores of chromian spinel are rimmed by ferritchromite and Cr-magnetite. The development of alteration rims around chromian spinel cores indicates their formation during prograde alteration and under oxidizing conditions during lower amphibolite facies metamorphism. Fresh chromian spinels are characterized by high contents of Cr2O3 (48.92-56.74 wt. %), Al2O3 (10.29-20.08wt. %), FeO (16.24-28.46 wt. %) and MgO (4.89-14.02 wt. %), and very low TiO2 contents (<0.16 wt. %). The analyzed fresh chromian spinels have high Cr# (0.62-0.79) characteristic of spinels in mantle peridotite that has undergone some degree of partial melting. The data presented here suggest that the mantle peridotites of the Gabal El-Degheimi area are similar to forearc peridotites of suprasubduction zone environments.

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Section: Tectonic Setting and Petrogenesismentioning

confidence: 95%

Section: Tectonic Setting and Petrogenesismentioning

confidence: 99%

Section: Alteration Of Chromian Spinelmentioning

confidence: 99%

Section: Correlations With Other Late Neoproterozoic Ultramafic Rocksmentioning

confidence: 99%

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Petrological studies of neoproterozoic serpentinized ultramafics of the nubian shield: spinel compositions as evidence of the tectonic evolution of egyptian ophiolites

Azer¹

2014

Acta Geologica Polonica

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“…Water is known to be present in the mantle wedge above supra-subduction zones (e.g., Ahmed and Arai 2002;Andal et al 2005;Uysal et al 2005). Specifically, in a fore-arc geotectonic regime both water and depleted mantle are available, thus providing the ideal conditions for the formation of boninitic melts (e.g., Crawford et al 1989;Pearce et al 2000;Khalil and Azer 2008). Boninite release from the Vourinos mantle is supported by the U-shaped normalized REE patterns of the harzburgitic rocks and elevated Cr# values of chromian spinel.…”

Section: Synthesis and Geotectonic Implicationsmentioning

confidence: 99%

Origin of mantle peridotites from the Vourinos Ophiolite Complex, Greece, as deduced from Cr-spinel morphological and chemical variations

Kapsiotis¹

2013

J. Geosci.

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The Vourinos Ophiolite Complex in north-western Greece represents a fragment of oceanic lithosphere emplaced after the Late Jurassic closure of the Neotethyan Pindos Ocean. This Ophiolite Complex consists mainly of a well-preserved mantle sequence dominated by peridotite and chromitite. Based on petrographic features, four distinct peridotite varieties can be distinguished in the Vourinos mantle suite: i) normal harzburgite (Opx ≥ 15 vol. %), ii) transitional harzburgite (Opx < 15 vol. %), iii) coarse-grained dunite and iv) fine-grained dunite. Chromian spinel morphology, based on DR# (degree of roundness) measurements, varies systematically from harzburgitic to dunitic rocks. Anhedral chromian spinel occurs in normal harzburgite (DR# < 0.40), whereas in the other studied peridotite types this mineral is more euhedral (DR# > 0.40). The Cr# [Cr/(Cr + Al)] in chromian spinel increases from normal harzburgite to coarse-grained dunite, varying between 0.47 and 0.84. Such a variation in chromian spinel composition indicates a multi-stage melting evolution for the Vourinos mantle suite. Chromian spinel from the fine-grained dunite bears similarities in terms of Cr# and Mg# [Mg/(Mg + Fe 2+ )] with chromian spinel from the neighboring chromitites, which implies a common origin for both lithologies. Chromian spinel morphological and compositional data indicate that after chromitite and fine-grained dunite formation a remnant boninite melt could have invaded the adjacent peridotites, modifying their accessory chromian spinels or even crystallizing new chromian spinel grains. Further evidence for that episode of melt percolation is provided by a few harzburgitic rock samples, which may be locally enriched in LREE exhibiting U-shaped chondrite-normalized REE patterns. Such patterns are characteristic of interaction between the depleted mantle peridotite and hydrous boninitic melt. The studied peridotites are interpreted as refractory residues whose initial composition was locally modified by mantle metasomatism in the fore-arc region of a supra-subduction zone.

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Mineralogy, geochemistry and geotectonic significance of harzburgites from the southern Dramala upper mantle suite, Pindos ophiolite complex, NW Greece

Kapsiotis

2014

Geological Journal

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The Dramala massif, located in the Dinarides–Hellenides orogenic belt, forms the mantle section of the Neotethyan Pindos ophiolite complex in NW continental Greece. Its southern domain is comprised mainly of voluminous harzburgite masses with variable clinopyroxene and olivine modal abundances, ranging from clinopyroxene‐bearing to typical and olivine‐rich harzburgites. The harzburgite varieties are characterized by elevated Cr# [Cr/(Cr + Al)] in Cr‐spinel (0.43–0.79), high forsterite (Fo) content in olivine (0.90–0.93), low Al2O3 content in clinopyroxene (≤1.77 wt.%) and poor whole‐rock abundances of Al2O3 (≤0.68 wt.%), CaO (≤0.68 wt.%), Sc (≤11 ppm) and REE, which are indicative of their refractory nature. In terms of fO2 values, the southern Pindos harzburgites plot between the FMQ‐2 (Fayalite–Magnetite–Quartz) and FMQ + 2 buffers. Simple batch and fractional melting models are not sufficient to explain their depleted composition. Their Ni/Yb ratios vs. Yb bulk‐rock abundances can be reproduced by up to 22–31% closed‐system non‐modal dynamic melting of an assumed spinel‐bearing lherzolite source. Cr‐spinel chemistry data suggest that the southern Dramala harzburgites were formed in an oceanic centre and then were reworked in the mantle wedge above a subducted slab. Combined petrographic and compositional data indicate that the studied harzburgites interacted with arc‐derived tholeiitic melts. This interaction resulted in substantial olivine and minor Cr‐spinel addition to the studied harzburgites, thus enhancing their refractoriness. Cryptic metasomatism was plausibly responsible for the demolition of any strong geochemical signatures suggestive of a previous melting event in a spreading centre. Comparable observations from the neighbouring Vourinos suite imply that the southern Dramala harzburgites probably represent an arc/fore‐arc mantle region within the mutual Pindos–Vourinos, Mesohellenic lithospheric mantle. Copyright © 2014 John Wiley & Sons, Ltd.

show abstract

Supra-subduction affinity in the Neoproterozoic serpentinites in the Eastern Desert, Egypt: Evidence from mineral composition

Cited by 75 publications

References 50 publications

Petrological studies of neoproterozoic serpentinized ultramafics of the nubian shield: spinel compositions as evidence of the tectonic evolution of egyptian ophiolites

Petrological studies of neoproterozoic serpentinized ultramafics of the nubian shield: spinel compositions as evidence of the tectonic evolution of egyptian ophiolites

Origin of mantle peridotites from the Vourinos Ophiolite Complex, Greece, as deduced from Cr-spinel morphological and chemical variations

Mineralogy, geochemistry and geotectonic significance of harzburgites from the southern Dramala upper mantle suite, Pindos ophiolite complex, NW Greece

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