Multistage petrogenetic evolution of Neoproterozoic serpentinized ultramafic rocks and podiform chromitites at Hagar Dungash, Eastern Desert of Egypt

2022 ◽  
Vol 369 ◽  
pp. 106507
Author(s):  
Hilmy E. Moussa ◽  
Heba S. Mubarak ◽  
Mokhles K. Azer ◽  
Adel A. Surour ◽  
Paul D. Asimow ◽  
...  
Keyword(s):  
Eastern Desert ◽  
Ultramafic Rocks ◽  
Podiform Chromitites

Temperatures of Neoproterozoic Regional Carbonate Alteration in the Eastern Desert of Egypt

2020 ◽  
Author(s):  
Arman Boskabadi ◽  
Tobias Kluge ◽  
Iain Pitcairn ◽  
Rabea Ali ◽  
Mokhles Azer ◽  
...  
Keyword(s):  
Low Temperature ◽  
Homogenization Temperature ◽  
Eastern Desert ◽  
Ultramafic Rocks ◽  
Wide Range ◽  
Two Samples ◽  
Ophiolitic Rocks ◽  
Clumped Isotope ◽  
Host Rocks ◽  
Different Sources

<p>Neoproterozoic ophiolites in the Eastern Desert (ED) of Egypt are pervasively carbonated and listvenitized. Two types of carbonation are recognized: 1) intergrown magnesite (and to lesser extent dolomite) with serpentine and talc that in cases form pure carbonate veins, and 2) cryptocrystalline magnesite veins filling the fractures crosscutting other ophiolitic host rocks. Few studies address the conditions of carbonate alteration of ultramafic rocks, especially the temperature of altering fluids. We employ clumped isotope thermometry on natural dolomite and magnesite from 17 variably carbonated ophiolitic rocks and veins in the ED. Five samples of antigorite-bearing serpentinite, talc-carbonate, and associated carbonate veins yield wide range temperatures of magnesite and dolomite between 213 to 426°C (285±73°C). These temperatures are comparable with previous fluid inclusion thermometry carried out on some of the vein samples (homogenization temperature between 225 to 383°C; Boskabadi et al. 2017). Ten samples of fully quartz-carbonate altered peridotites (i.e. listvenites) record even a wider range of clumped isotope carbonation temperatures between 90 and 452°C (227±112°C). In contrast, two samples of late-stage veins of cryptocrystalline magnesite record lower temperatures of 19 and 28°C. While the constraints on the pressure of carbonation are lacking, the wide range of temperatures for the carbonates in antigorite-bearing serpentinite, talc-carbonate, and listvenite lithologies suggest that carbonation probably occurred at variable depths, whereas the low temperature of cryptocrystalline magnesite veins points to conditions nearer the surface most likely associated with post-obduction processes. Therefore, different sources of carbon and CO<sub>2</sub>-bearing fluids should have been responsible for the formation of high- and low-temperature carbonates in the region.</p><p> </p><p>  Boskabadi et al. 2017. International Geology Review 59, 391–419.</p>

scholarly journals Petrogenesis of Neoproterozoic Ultramafic Rocks, Wadi Ibib–Wadi Shani, South Eastern Desert, Egypt: Constraints from Whole Rock and Mineral Chemistry

2021 ◽  
Vol 11 (22) ◽  
pp. 10524
Author(s):  
El Saeed R. Lasheen ◽  
Gehad M. Saleh ◽  
Farrage M. Khaleal ◽  
Mamdooh Alwetaishi
Keyword(s):  
Mineral Chemistry ◽  
Eastern Desert ◽  
Ultramafic Rocks ◽  
Abyssal Peridotite ◽  
Bulk Rock ◽  
Secondary Minerals ◽  
South Eastern ◽  
Temperature Ranges ◽  
Ophiolitic Rocks ◽  
Primary Minerals

This contribution deals with new geology, petrography, and bulk-rock/mineral chemistry of the poorly studied ultramafics of Wadi Ibib–Wadi Shani (WI–WS) district, South Eastern Desert, Egypt. These ultramafics are dismembered ophiolitic rocks that can be subdivided into serpentinites and serpentinized peridotites. Primary minerals such as olivine and pyroxene are absent in serpentinites, but relics of them occur in serpentinized peridotites. Pseudomorph after olivine is indicated by common hourglass textures with less mesh, whilst schistose bastites reflect a pyroxene pseudomorph. Chromite can be subdivided into Cr-spinel and Al-spinel. Cr-spinel ranges from chromite to magnesochromite in composition, whereas Al-spinel belongs to the spinel field. Cr-spinel includes YCr (Cr/(Cr+Al+Fe+3), YAl (Al/(Al+Cr+Fe+3), and YFe+3 (Fe+3/(Fe+3+Al+Cr), similar to forearc peridotite, whilst Al-spinel is more similar to abyssal peridotite, and may be formed during inanition of subduction processes in proto forearc environments. The main secondary minerals are tremolite, talc, and chlorite—which is subdivided into pycnochlorite and diabantite—and their temperature ranges from 174 to 224 °C. The examined rocks had undergone high partial melting degrees (>25%), as indicated by the Cr# of their unaltered cores (Cr-spinel, >0.6), whole rocks (Al2O3, SiO2, CaO, and MgO), trace and REEs, depleted Na2O, Al2O3, and Cr2O3 of clinopyroxene, and high forsterite content ((Fo = 100 Mg/Mg + Fe), av. 95.23 mol%), consistent with forearc settings.

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

2014 ◽  
Vol 64 (1) ◽  
pp. 123-137 ◽  
Author(s):  
Mokhles K. Azer
Keyword(s):  
Tectonic Evolution ◽  
Mantle Peridotite ◽  
Eastern Desert ◽  
Ultramafic Rocks ◽  
Chromian Spinel ◽  
Central Eastern Desert ◽  
Suprasubduction Zone ◽  
Mantle Peridotites ◽  
Nubian Shield ◽  
Ophiolitic Rocks

Abstract 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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