Abu Hamamid Neoproterozoic Alaskan-type complex, south Eastern Desert, Egypt

Farahat, Esam S.; Helmy, Hassan M.

doi:10.1016/j.jafrearsci.2006.02.003

Cited by 73 publications

(65 citation statements)

References 40 publications

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“…It is believed that the continuous reaction with enstatite led to the enrichment of Al and Mg in the Cr-spinel, whereas the enstatite became enriched in Cr and Fe. Similar interpretations were assigned to reverse zonation in spinel grains from the Rhum-layered mafic-ultramafic complex in Scotland [37] and also to spinel grains from the Gabbro Akarem Alaskan-type mafic-ultramafic complex in Egypt [24,75,76].…”

Section: Elemental Exchange With Coexisting Silicate Mineralsmentioning

confidence: 54%

Origin of Reverse Zoned Cr-Spinels from the Paleoproterozoic Yanmenguan Mafic–Ultramafic Complex in the North China Craton

Bai

Xiao

et al. 2018

Minerals

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Abstract:We conducted petrological and mineral chemistry investigations of Cr-spinel in ultramafic rocks of the Yanmenguan mafic-ultramafic complex in the North China Craton. The Cr-spinel grains occur as inclusions in enstatite, tschermakite, phlogopite, and olivine, or as interstitial grains among the aforementioned silicate minerals, and show concentric or asymmetrical textures. Back-scattered electron and elemental images and compositional profiles of the spinel grains indicate the presence of Cr-and Fe-rich cores and Al-and Mg-rich rims. The host silicate minerals display a decrease in Al and Mg contents accompanied by an increase in Cr and Fe away from the spinel. These textures and compositional variations suggest that subsolidus elemental exchange more likely gave rise to the compositional zonation, resulting in the transfer of Al and Mg from the silicate minerals to the spinel. The Mn, Ni, and Ti contents in spinel and the major elements of olivine-hosted spinel are relatively stable during subsolidus elemental diffusion and thus are more reliable tracers of primary high-temperature processes. The temperature estimates reveal that the subsolidus diffusion might have occurred at 600-720 • C, which could be linked to the regional metamorphic event.

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Section: Elemental Exchange With Coexisting Silicate Mineralsmentioning

confidence: 54%

Origin of Reverse Zoned Cr-Spinels from the Paleoproterozoic Yanmenguan Mafic–Ultramafic Complex in the North China Craton

Bai

Xiao

et al. 2018

Minerals

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“…The thrust ophiolites are generally dismembered, representing remnants of oceanic lithosphere that coexisted with the ANS Neoproterozoic intra-oceanic arcs. The intrusive mafic-ultramafic complexes form undeformed, small, elliptical outcrops and are commonly concentrically zoned or layered intrusions as well as dyke-like intrusions (Helmy and El Mahallawi 2003;Farahat and Helmy 2006;Azer and Gharbawy 2011;Azer et al 2012). Neoproterozoic ophiolites are common in the central and southern sectors of the Eastern Desert of Egypt (Text- fig.…”

Section: Regional Geologymentioning

confidence: 99%

“…On the other hand, the ultramafic rocks of layered mafic-ultramafic intrusions show a wide variation in rock types, including wehrlite, dunite, lherzolite and pyroxenites with minor harzburgite. (Khudeir 1995;Helmy and El-Mahallawi 2003;Farahat and Helmy 2006;Helmy et al 2008;Azer and ElGharabawy 2011). The present study suggests harzburgite and dunite protoliths for the serpentinites of Gabal El-Degheimi due to the abundance of bastite and mesh textures, similar in this regard to the ophiolitic serpentinites of the ANS.…”

Section: Correlations With Other Late Neoproterozoic Ultramafic Rocksmentioning

confidence: 99%

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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“…Recent isotopic studies of one of these complexes revealed a Sm/Nd age of 770 Ma (Helmy et al, 2005). The evidence for island arc setting of these complexes comes from the general geologic context, field relations, mineralogy, and mineral and bulk -rock chemistry (Helmy and El Mahallawi, 2003;Farahat and Helmy, 2006).…”

Section: Geological Background and Petrographymentioning

confidence: 99%

Corona structure from arc mafic-ultramafic cumulates: The role and chemical characteristics of late-magmatic hydrous liquids

Helmy

Yoshikawa

Shibata

et al. 2008

Journal of Mineralogical and Petrological Sciences

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The Genina Gharbia mafic -ultramafic complex consisting of peridotite, pyroxenite, and gabbronorite represents a remnant of a hydrous magma chamber that was crystallized at the mantle -crust boundary. The hydrous nature of the magma is expressed in the high modal (up to 60%) of amphibole in cumulates and is reflected in variable textural and chemical features of the complex. One of the important manifestations of the hydrous nature is the development of a corona structure between olivine and plagioclase. The corona texture and mineralogy varied according to the activity of the interstitial liquid, temperature, and P H 2 O . The corona in peridotite is limited to thin (<100 microns) orthopyroxene and/or amphibole shells. Thick orthopyroxene -(orthopyroxene -spinel symplectites) -clinopyroxene -amphibole coronas are common in norite. Extensive analysis of different minerals of various textures by electron microprobe and laser ablation inductively coupled plasma mass spectrometry (LA -ICP -MS) revealed distinct chemical difference between the interstitial and cumulus phases of the corona. The corona pyroxenes and amphibole are depleted in V, Ti, Zr, and Nb and enriched in LREE, reflecting the LI-LE -rich and HFSE -depleted nature of the evolved hydrous liquid. The textural and chemical features of the corona are consistent with the formation of corona minerals at the late -magmatic stage. The orthopyroxene corona in peridotite crystallized directly from the evolved melt, while the amphibole corona developed at the expense of plagioclase. Variable corona minerals in norite are the result of direct crystallization from progressively evolved magma during cooling and continuous increase in P H 2 O .

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Abu Hamamid Neoproterozoic Alaskan-type complex, south Eastern Desert, Egypt

Cited by 73 publications

References 40 publications

Origin of Reverse Zoned Cr-Spinels from the Paleoproterozoic Yanmenguan Mafic–Ultramafic Complex in the North China Craton

Origin of Reverse Zoned Cr-Spinels from the Paleoproterozoic Yanmenguan Mafic–Ultramafic Complex in the North China Craton

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

Corona structure from arc mafic-ultramafic cumulates: The role and chemical characteristics of late-magmatic hydrous liquids

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