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Post-collisional volcanism with adakitic signatures in the Arabian-Nubian Shield: A case study of calc-alkaline Dokhan volcanics in the Eastern Desert of Egypt

Abuamarah, Bassam A. and Azer, Mokhles K. and Asimow, Paul D. and Shi, Qingshang (2021) Post-collisional volcanism with adakitic signatures in the Arabian-Nubian Shield: A case study of calc-alkaline Dokhan volcanics in the Eastern Desert of Egypt. Lithos, 388-389 . Art. No. 106051. ISSN 0024-4937. doi:10.1016/j.lithos.2021.106051.

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A volcano-sedimentary succession, including the Guruf volcanic series, is exposed at Gabal Um Guruf in the north Eastern Desert of Egypt. A series of intermediate to silicic volcanic flows and associated pyroclastic deposits unconformably overlie quartz-diorite and granodiorite plutons and are intruded by high-level alkali feldspar granites. The metavolcanic xenoliths in the granodiorite are shown to be unrelated to the Guruf volcanics. Two volcanic cycles can be recognized. The lower unit is a high-K calc-alkaline series with minor basaltic andesite and mostly andesite through dacite. The upper unit consists of rhyolite and rhyodacite that is transitional towards alkaline, A-type magma. Both units are assigned to the Dokhan volcanics and interpreted as post-collisional. REE patterns are characterized by slow progressive enrichment throughout the suite, with heavy REE apparently acting more incompatibly than light REE; concave-upwards REE patterns in basalt andesite suggest residual amphibole in the source. Only the upper rhyolite displays prominent negative Eu anomalies (Eu/Eu* = 0.35–0.73). Apparent crystallization temperatures of primary pyroxene are 800–1000 °C and of primary amphiboles 781–944 °C. The major and trace element chemistry of the suite can be modeled as a single liquid line of descent, with pressure decreasing as the magma cools and evolves, and a prominent role for apatite in sequestering CaO, P₂O₅, and light REE. Although upper crustal contamination and magma mixing cannot be ruled out, the data do not require them. The suite includes pyrophanite, an unusual Mn-rich ilmenite-group solid solution, not previously recorded in volcanic rocks in the Arabian-Nubian Shield (ANS). The Guruf volcanic series is undeformed and unmetamorphosed, unlike the typical subduction-related volcanic units of the ANS. The geochemical characteristics are consistent with those of many post-collisional ANS rocks. The mostly calc-alkaline character and other traits previously interpreted to indicate an active arc setting instead more likely reflect remelting of earlier arc-related material from the pre-collisional stage (850–740 Ma). The lava flows of the lower succession have adakitic characteristics, including high Sr, low Y, low Yb, high Sr/Y, and high (La/Yb)n. This likely reflects the influence of residual or fractionated amphibole in the ANS crust, rather than slab melting during active subduction. A post-collisional episode of delamination and heating of tonalitic lower crustal material, followed by mixing with asthenospheric mantle, created a primary magma with the characteristics of the Guruf basaltic andesite, including residual amphibole. There is no need for either late subduction in the area or long-term persistence of subduction-influenced material in the local convecting mantle.

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Azer, Mokhles K.0000-0002-3711-8630
Asimow, Paul D.0000-0001-6025-8925
Additional Information:© 2021 Published by Elsevier B.V. Received 21 December 2020, Revised 9 February 2021, Accepted 11 February 2021, Available online 15 February 2021. The authors would like to extend their appreciation and gratitude to the King Saud University for funding and supporting this work through Researchers Supporting Project number (RSP-2020/151), King Saud University, Riyadh, Saudi Arabia. PDA's participation is supported by NSF award 1947616. We thank Einari Suikkanen for creating and sharing the easyMelts interface and Paula Antoshechkina for supporting the alphaMELTS trace element modeling capability. Finally, thorough reviews by the two reviewers as well as comments by Prof. Michael Roden (editor) greatly improved the present version of the manuscript. 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.
Funding AgencyGrant Number
King Saud UniversityRSP-2020/151
Subject Keywords:Arabian–Nubian Shield; Post-collisional volcanics; Lithospheric delamination; Adakite; Pyrophanite
Record Number:CaltechAUTHORS:20210216-131515139
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Official Citation:Bassam A. Abuamarah, Mokhles K. Azer, Paul D. Asimow, Qingshang Shi, Post-collisional volcanism with adakitic signatures in the Arabian-Nubian Shield: A case study of calc-alkaline Dokhan volcanics in the Eastern Desert of Egypt, Lithos, Volumes 388–389, 2021, 106051, ISSN 0024-4937, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:108069
Deposited By: Tony Diaz
Deposited On:16 Feb 2021 21:23
Last Modified:16 Nov 2021 19:08

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