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Assessment of magmatic versus post-magmatic processes in the Mueilha rare-metal granite, Eastern Desert of Egypt, Arabian-Nubian Shield

Seddik, Amany M. A. and Darwish, Mahmoud H. and Azer, Mokhles K. and Asimow, Paul D. (2020) Assessment of magmatic versus post-magmatic processes in the Mueilha rare-metal granite, Eastern Desert of Egypt, Arabian-Nubian Shield. Lithos, 366-367 . Art. No. 105542. ISSN 0024-4937. https://resolver.caltech.edu/CaltechAUTHORS:20200421-125254344

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Abstract

The Mueilha rare-metal granite, exposed in the central Eastern Desert of Egypt, is a post-collisional intrusion that formed in the final magmatic stage of the evolution of the Arabian-Nubian Shield. The Mueilha intrusion was emplaced as a high-level magmatic cupola into metamorphic country rocks. It consists of two cogenetic intrusive bodies: an early phase emplaced at shallow depth and now penetratively altered to white albite granite and a later phase of red granites emplaced at greater depth that better preserve magmatic features. The albite granite is less common and represents the upper margin of the Mueilha intrusion, the apex of the magmatic cupola. The red granites are volumetrically dominant and appears to have crystallized from the margins inward, forming a composite pluton zoned from muscovite granite to alkali feldspar granite. All parts of the Mueilha pluton appear to have been emplaced within a short time interval, before complete crystallization of the earliest phase. The geochemistry of the Mueilha granites is typical of rare-metal granites, characterized by high SiO₂, Na₂O + K₂O, Nb, Rb, Ta, Y, U, Th, Sn, and W with depletion in P, Mg, Ti, Sr and Ba. They are weakly peraluminous and highly fractionated with A-type character. The chondrite-normalized REE patterns have strongly negative Eu anomalies, typical of highly differentiated granites that evolved through a transitional magmatic–hydrothermal stage. The primary magma feeding the Mueilha intrusion was generated by partial melting of the juvenile crust of the Arabian-Nubian Shield; it subsequently underwent extensive fractional crystallization and metasomatism by late- to post-magmatic fluids. Separation of fluids from the oversaturated melt promoted both diffuse greisenization and focused segregation of pegmatite and fluorite and quartz veins. Alkalis liberated from feldspars consumed by greisenization were redeposited during albitization in the uppermost part of the magma chamber. Despite penetration of the intrusion boundary by discrete dikes, veins, and aphophyses, diffuse alteration of the metamorphic country rocks is not apparent. Primary columbite-series minerals crystallized from the melt and were later partly replaced by secondary Nb and Ta minerals (fluorcalciomicrolite and wodginite) during hydrothermal alteration.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1016/j.lithos.2020.105542DOIArticle
ORCID:
AuthorORCID
Azer, Mokhles K.0000-0002-3711-8630
Asimow, Paul D.0000-0001-6025-8925
Additional Information:© 2020 Elsevier B.V. Received 2 March 2020, Revised 15 April 2020, Accepted 15 April 2020, Available online 21 April 2020. We acknowledge the National Research Centre, Egypt for supporting this study as a part of the internal project (No. 12010306) of studies of the rare-metal bearing granites in the Eastern Desert of Egypt. This work is a part of the master's thesis of Amany M.A. Seddik (the first author). PDA is support by the US NSF through award 1550934. The authors highly appreciate thoughtful reviews by the two anonymous reviewers. In addition, the authors are also indebted to the editor (Prof. Michael Roden) for his efforts and numerous helpful comments. The authors declare no competing financial interests or personal relationships that could have influenced the work presented herein.
Funders:
Funding AgencyGrant Number
National Research Centre (Egypt)12010306
NSFEAR-1550934
Subject Keywords:Arabian-Nubian Shield; Highly fractionated granite; Nb–Ta oxide minerals; Magmatic–hydrothermal evolution
Record Number:CaltechAUTHORS:20200421-125254344
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20200421-125254344
Official Citation:Amany M.A. Seddik, Mahmoud H. Darwish, Mokhles K. Azer, Paul D. Asimow, Assessment of magmatic versus post-magmatic processes in the Mueilha rare-metal granite, Eastern Desert of Egypt, Arabian-Nubian Shield, Lithos, Volumes 366–367, 2020, 105542, ISSN 0024-4937, https://doi.org/10.1016/j.lithos.2020.105542. (http://www.sciencedirect.com/science/article/pii/S0024493720301808)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:102699
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:21 Apr 2020 20:05
Last Modified:29 Apr 2020 16:26

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