Maurice, Ayman E. and Azer, Mokhles K. and Asimow, Paul D. and Basta, Fawzy F. and Helmy, Hassan M. and Shibata, Tomoyuki (2021) The kabr El-Bonaya peridotites, Southeastern Sinai, Egypt: petrology, geochemistry, and metamorphism of Neoproterozoic arc ultramafic cumulates. American Journal of Science, 321 (10). pp. 1445-1496. ISSN 0002-9599. doi:10.2475/10.2021.02. https://resolver.caltech.edu/CaltechAUTHORS:20220112-792687509
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Abstract
Two small, isolated ultramafic masses in the northeastern part of the Wadi Kid area, southeast Sinai, are composed of variably serpentinized harzburgite and lherzolite with minor talc-anthophyllite rock. The primary phases are dominantly olivine, orthopyroxene and Cr-spinel; clinopyroxene, amphibole, and phlogopite are also found in lherzolite samples. The whole-rock Mg# of harzburgite samples (89–91) is higher than that of lherzolite (average 82). The harzburgite samples contain olivine with higher Mg and Ni contents, orthopyroxene with higher Mg#, and Cr-spinel with higher Cr content than do the lherzolite samples. The REE patterns of clinopyroxene and amphibole in lherzolite are most consistent with a cumulate origin. Although several compositional characteristics of the harzburgites resemble those of residual mantle, in detail the Cr₂O₃ and Al₂O₃ contents of fresh Cr-spinel in harzburgite are different from those found in mantle samples or in any of the Neoproterozoic ophiolitic peridotites throughout the Arabian-Nubian Shield. Thus, all the ultramafic rocks at Kabr El-Bonaya are best explained as ultramafic cumulates, with harzburgite consisting of early-formed cumulate phases and lherzolite containing later-formed cumulate phases with higher REE abundances, primary hydrous minerals, evolved primary silicates, and high TiO₂ (0.77 wt.%) and Al₂O₃ (18 wt.%) contents in Cr-spinel. The trace-element characteristics of the rocks indicate a subduction-related parental magma: whole-rock chondrite-normalized REE patterns are LREE-enriched; calculated fO₂ values are elevated (+2.47 to +3.39 log units above the fayalite-magnetite-quartz buffer); and computed N-MORB-normalized trace element patterns for melts in equilibrium with clinopyroxene and amphibole have negative Nb-Ta anomalies and enrichment in large-ion lithophile elements. The low Al₂O₃/SiO₂ ratios (0.007–0.040) of harzburgite samples and the low TiO₂ contents and high Cr# of their Cr-spinel indicate derivation from a mantle source that experienced high-degree partial melting. From these characteristics, we infer a boninitic parental melt for the harzburgite. We offer an illustrative quantitative fractionation model that can explain the successive derivation of harzburgite and lherzolite cumulates along a single equilibrium, polybaric cooling path. We conclude that the Kabr El-Bonaya ultramafic cumulates represent the exposed roots of a Neoproterozoic island arc that was caught in the collision between East and West Gondwana.
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| Additional Information: | © 2021 American Journal of Science. Dr. Aley El-Shazly, Marshall University, USA, is acknowledged for help in the trace element analyses of some samples. We thank Dr. Mohamed Madbouly, formerly at the Geological Survey of Egypt, for discussion on the origin of the KB ultramafic rocks. The present version of the manuscript benefited from comments by James Worthington, Shu-Guang Song, Ghaleb Jarrar and the Associate Editor. Over the development of the data and ideas in this paper, PDA was supported by the US NSF through award 1947616. | |||||||||
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| Subject Keywords: | Neoproterozoic, Island Arcs, Ultramafic cumulates, Arabian-Nubian Shield, Sinai | |||||||||
| Issue or Number: | 10 | |||||||||
| DOI: | 10.2475/10.2021.02 | |||||||||
| Record Number: | CaltechAUTHORS:20220112-792687509 | |||||||||
| Persistent URL: | https://resolver.caltech.edu/CaltechAUTHORS:20220112-792687509 | |||||||||
| Official Citation: | The kabr El-Bonaya peridotites, Southeastern Sinai, Egypt: petrology, geochemistry, and metamorphism of Neoproterozoic arc ultramafic cumulates Ayman E. Maurice, Mokhles K. Azer, Paul D. Asimow, Fawzy F. Basta, Hassan M. Helmy, Tomoyuki Shibata American Journal of Science Dec 2021, 321 (10) 1445-1496; DOI: 10.2475/10.2021.02 | |||||||||
| Usage Policy: | No commercial reproduction, distribution, display or performance rights in this work are provided. | |||||||||
| ID Code: | 112846 | |||||||||
| Collection: | CaltechAUTHORS | |||||||||
| Deposited By: | George Porter | |||||||||
| Deposited On: | 12 Jan 2022 11:40 | |||||||||
| Last Modified: | 12 Jan 2022 23:50 |
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- The kabr El-Bonaya peridotites, Southeastern Sinai, Egypt: petrology, geochemistry, and metamorphism of Neoproterozoic arc ultramafic cumulates. (deposited 12 Jan 2022 11:40) [Currently Displayed]
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- Maurice, Ayman E. and Azer, Mokhles K. and Asimow, Paul D. and Basta, Fawzy F. and Helmy, Hassan M. and Shibata, Tomoyuki The kabr El-Bonaya peridotites, Southeastern Sinai, Egypt: petrology, geochemistry, and metamorphism of Neoproterozoic arc ultramafic cumulates. (deposited 12 Jan 2022 11:40) [Currently Displayed]
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