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Bimodal zircon ages from Natash volcanics (southeast Egypt) and the link between eruption mechanisms and Late Cretaceous tectonics

By Mohamed Ali Abu El-Rus, Jean-Louis Paquette, Gilles Chazot and Riccardo Vannucci

Abstract

International audienceTrachyte plugs from the Natash volcanic field have been precisely dated using in situ U-Pb geochronology on zircon grains at~93 Ma. Available zircon ages thus suggest that the overall volcanic history at Natash was probably shorter than previouslyestimated based on Rb-Sr and K-Ar ages, which are more sensitive to element mobility. Basaltic flows and trachyte plugs wereproduced by a largely synchronous, Upper Cretaceous volcanic activity that occurred in the Natash area at the onset of theextensional fracturing that preceded and accompanied the doming of the Afro-Arabian Shield. Extraction and eruption ofvolumetrically dominant basalts from deeper lithospheric levels were ruled by major NW-SE strike-slip faults, whereas bothmajor and subordinate fault systems activated by successive tectonic pulses favoured the ascent of more evolved melts (i.e.trachytes and rhyolites) from shallow-level magma chambers. The study revealed also the presence of zircon xenocrysts in sometrachyte plugs associated or not to magmatic zircon. These xenocrysts have pre-Cambrian ages (~681 Ma) matching those ofzircons from basement rocks in the area (~700 Ma) and were most probably incorporated during the emplacement of trachyteplugs at shallow depths. The strictly bimodal ages recorded by zircons suggest a very large time gap (> 500 Ma) between the endof the Pan-African Orogeny and the onset of new tectono-magmatic activity in the Natash area

Topics: Eastern Desert Egypt, Cretaceous volcanism, Natash volcanics, Trachyte plugs, U-Pb zircon ages, [SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry
Publisher: 'Springer Science and Business Media LLC'
Year: 2019
DOI identifier: 10.1007/s12517-019-4457-2
OAI identifier: oai:HAL:hal-02117469v1
Provided by: HAL-UJM
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