International Geologiical Congress - Oslo 2008

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HPP-07 Late Neoproterozoic orogenic belts and assembly of Gondwana

 

Neoproterozoic SHRIMP U-Pb zircon ages of Dokhan volcanics in the northern part of the eastern desert, Egypt

 

Christoph Breitkreuz, TU Bergakademie Freiberg (Germany)
Hassan Eliwa, Minufiya University (Egypt)
Ibrahim Khalaf, Minufiya University (Egypt)
Khaled El Gameel, Minufiya University (Egypt)
Sergei Sergeev, VSEGEI (Russian Federation)
Alexander Larionov, VSEGEI (Russian Federation)
Uwe Hoffmann, TU Bergakademie Freiberg (Germany)
 

 

Stratigraphic concepts on the late Proterozoic evolution of volcanosedimentary successions and plutonic complexes remain controversial for many regions of the Nubian-Arabic Shield. We present SHRIMP dating on zircons separated from eight SiO2-rich ignimbrites and one subvolcanic dacitic body. Samples were taken from the main outcrops of the so-called Dokhan Volcanics in the northern Eastern Desert; these are (from north to south) Wadi Qaa, Jebel Kharaza, Jebel Urf, Jebel Monghul, Wadi Dib, Wadi Bali and Jebel Nuqara. For detailed informations on the volcanosedimentary successions at Jebel Urf and Jebel Kharaza see Eliwa et al. (this volume).

Each zircon separate has been characterized by SEM and CL imaging. For each sample concordant data of 8 to 14 spots were used to calculate the formation age of the volcanic and subvolcanic rocks ranging between 592 ± 5 Ma and 618 ± 4 Ma. No systematic north-south trend in the northern Eastern desert is apparent from the age data. The observed wide range of formation ages suggests the existence of more than one volcanic phase.

Only zircon separates from Wadi Qaa, Jebel Urf and Jebel Kharaza samples occasionally contain inherited zircons with ages of 669, 735 and 746 Ma, respectively. This observation concurs with the published model of a predominantly juvenile nature of this part of the Pan-African orogenic belt.

An ignimbrite sample from a non-metamorphic volcanosedimentary succession cropping out northeast of Jebel Kharaza yielded an emplacement age of 727 ± 7 Ma (10 concordant spots). With preservation as to further investigation, this finding points to the existence of pre-Ediacaran non-metamorphic successions in the northern Eastern Desert of Egypt.

 

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