Geochemical Constraints of the Ediacaran Volcano-Sedimentary Succession of the Sa’al Metamorphic Complex at Wadi Zaghra, South Sinai, Egypt
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Special thanks to Prof. Paul D. Asimow, California Institute of Technology, for his help with the microprobe analyses at Caltech. Also, the authors are grateful to Prof. E. El-Hinnawi, Professor of Mineralogy and Geochemistry, Earth Sciences Department, National Research Centre, Cairo, for critically reviewing the manuscript and for his comments and constructive remarks to improve it. Comments by the reviewers improved the present version of the manuscript. Dr Susan Turner and Dr. Fei Hongcai assisted with English.

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    Abstract:

    The volcano-sedimentary succession around Wadi Zaghra in Sinai, at the northernmost segment of the Arabian Nubian Shield, comprises volcanic rocks interbedded with rather immature sediments. The succession is dominated by intermediate to silicic volcanics of medium- to high-K calc-alkaline affinity. It is divided into two units, the lower unit includes intermediate rocks and dacites interbedded with graywackes, semi-pelites and pelites and topped by polymict conglomerates. This unit is subjected to folding and regional metamorphism (up to garnet zone) and is intruded by quartz diorite-granodiorite inducing, locally, low-pressure contact thermal metamorphism. The unmetamorphosed upper unit encompasses acid volcanics intercalated with litharenite, sublitharenite and minor arenite. The rhyolites of this unit pertain to the highly fractionated granites and are characterized by an agpaitic index (NK/A) ranging from 0.87 to 0.96. They may reflect either extensive interaction of subduction-related magmas with the continental crust or a change in the tectonic regime. The present lithological and geochemical characteristics of the studied sediments together with available zircon ages indicate rather distal provenance of their detritus. This detritus comprises fluvial-alluvial sediments accumulated in the intermontane basins, which are half-grabens or tilted fault blocks. The tectonic setting of the depositional basins is active continental margin and continental island arcs. Geochemical patterns of the Zaghra volcano-sedimentary succession indicate their correlation with the Dokhan Volcanics-Hammamat Clastics sequence of the Eastern Desert of Egypt. Also, the Zaghra volcanics display geochemical similarities with those exposed in Sinai, at the Rutig, Ferani and Iqna Shar’a areas. The Zaghra succession is dated as Ediacaran but is not related either to the ensimatic island arc assemblage or to the rift-related assemblage formed during the early stages of the break-up of Rodinia as previously thought.

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SAMUEL D. Michael, MOUSSA E. Hilmy, AZER K. Mokhles, SADEK GHABRIAL Doris.2019. Geochemical Constraints of the Ediacaran Volcano-Sedimentary Succession of the Sa’al Metamorphic Complex at Wadi Zaghra, South Sinai, Egypt[J]. Acta Geologica Sinica(),93(1):50-73

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History
  • Received:July 31,2018
  • Revised:
  • Adopted:
  • Online: February 20,2019
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