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Evolution of a Neoproterozoic island arc in the northern Arabian-Nubian Shield: Volcanic rocks and their plutonic equivalents in the Hamash area, south Eastern Desert, Egypt

Gharib, Moustafa E. and Maurice, Ayman E. and Ahmed, Ahmed H. and Asimow, Paul D. and Bakhit, Bottros R. and Selim, Hussam A. (2021) Evolution of a Neoproterozoic island arc in the northern Arabian-Nubian Shield: Volcanic rocks and their plutonic equivalents in the Hamash area, south Eastern Desert, Egypt. Precambrian Research, 358 . Art. No. 106145. ISSN 0301-9268. doi:10.1016/j.precamres.2021.106145. https://resolver.caltech.edu/CaltechAUTHORS:20210405-124500443

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Abstract

A suite of Neoproterozoic island arc volcanic and plutonic rocks are exposed in the Hamash area of the south Eastern Desert of Egypt. The volcanic assemblage includes metabasalt, a group of andesites with subordinate basalts (the Hamash Volcanics), and felsic volcanic porphyry. The plutonic rocks include a diorite-tonalite series, fine-grained granite, and granite porphyry. The volcanic rocks are generally sub-alkaline and feature a strong depletion in Nb and Ta. The metabasalt belongs to the low-K tholeiitic series and has nearly flat rare-earth element patterns. Its compositional characteristics indicate generation by partial melting of a depleted mantle source in an immature oceanic island arc setting. On the other hand, the basalt, andesite and felsic volcanic porphyry have low- to medium-K calc-alkaline affinity and are enriched in light rare-earth elements and large ion lithophile elements. Their parental magmas likely formed by fluid-assisted partial melting of a less depleted mantle source with major subduction input, in a mature island arc setting. The andesite cannot be derived from the basalt by fractional crystallization; their parental magmas likely represent different degrees of melting underneath crust of different thickness. Estimation of the arc crustal thickness during formation of these rocks yields ~ 5 km for the metabasalt, ~20 km for the Hamash basalt, and ~ 30 km for the Hamash andesite, consistent with a progression in maturity of the arc over time. The geochemical characteristics of the diorite-tonalite series suggest that it represents an intrusive equivalent of the medium-K calc-alkaline Hamash andesite, and the fine-grained granite represents residual liquid after continued fractionation of the parental magma of the andesite and diorite-tonalite. We present thermodynamic fractionation models that constrain the conditions of fractionation for the andesite, diorite-tonalite, and fine-grained granite suite. The compositional similarity of the granite and rhyolite porphyries, especially their SiO₂ and Al₂O₃ contents and Y/Nb ratios, indicate generation by partial melting of similar crustal sources, although greater assimilation of upper crust is evident in elevated Rb/Sr ratios and K₂O and light rare-earth element concentrations in the granite porphyry. We conclude that the magmatic rocks of the Hamash area represent an arc crustal section that records the evolution of a Neoproterozoic oceanic island arc. The arc was later caught up in the assembly of the northern Arabian-Nubian Shield.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1016/j.precamres.2021.106145DOIArticle
ORCID:
AuthorORCID
Asimow, Paul D.0000-0001-6025-8925
Additional Information:© 2021 Elsevier B.V. Received 26 July 2020, Revised 25 January 2021, Accepted 19 February 2021, Available online 3 April 2021. The Hamash Gold Company is acknowledged for logistical support during three seasons of field work. We thank Dr. Ahmed Shwail for guidance in some parts of the study area. This contribution benefited from comments of Moshe Eyal and Aley El-Shazly. PDA is supported by the US NSF, award 1947616. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Funders:
Funding AgencyGrant Number
NSFEAR-1947616
Subject Keywords:Neoproterozoic; Arc evolution; Magma generation; Arabian-Nubian Shield; Eastern Desert; Egypt
DOI:10.1016/j.precamres.2021.106145
Record Number:CaltechAUTHORS:20210405-124500443
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20210405-124500443
Official Citation:Moustafa E. Gharib, Ayman E. Maurice, Ahmed H. Ahmed, Paul D. Asimow, Bottros R. Bakhit, Hussam A. Selim, Evolution of a Neoproterozoic island arc in the northern Arabian-Nubian Shield: Volcanic rocks and their plutonic equivalents in the Hamash area, south Eastern Desert, Egypt, Precambrian Research, Volume 358, 2021, 106145, ISSN 0301-9268, https://doi.org/10.1016/j.precamres.2021.106145. (https://www.sciencedirect.com/science/article/pii/S0301926821000553)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:108621
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:09 Apr 2021 01:20
Last Modified:09 Apr 2021 01:20

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