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Late Neoproterozoic Tectonics and Geodynamics in NE-Africa – Eastern Desert – Egypt.

From 1993 onwards our group accomplished projects founded by the Austrian Science Foundation (FWF) in Egypt. Focus is recognition of thrust and extension tectonics during oblique plate convergence and interplay with magmatic, metamorphic, sedimentary and ore forming processes.

Some outcomes:
Regional cooling in the course of Neoproterozoic core complex exhumation in the Central Eastern Desert of Egypt is constraint by 40Ar/39Ar ages of hornblende and muscovite from Meatiq, Sibai and Hafafit domes. The data reveal highly diachronous cooling with hornblende ages clustering around 580 Ma in the Meatiq and the Hafafit, and 623 and 606 Ma in the Sibai. These 40Ar/39Ar ages are interpreted together with previously published structural and petrological data, radiometric ages obtained from Neoproterozoic plutons, and data on sediment dynamics from the intramontane Kareim molasse basin. Early-stage low velocity exhumation was triggered by magmatism initiated at ca. 650 Ma in the Sibai and caused early deposition of molasses sediments within rim synforms. Rapid late stage exhumation was released by combined effect of strike-slip and normal faulting, exhumed Meatiq and Hafafit domes and continued until ca. 580 Ma. We propose a new model that adopts core complex exhumation in oblique island arc collision-zones and includes transpression combined with lateral extrusion dynamics. In this model, continuous magma generation weakened the crust leading to facilitation of lateral extrusion tectonics. Since horizontal shortening is balanced by extension, no major crustal thickening and no increase of potential energy (gravitational collapse) is necessarily involved in the process of core complex formation. Core complexes were continuously but slowly exhumed without creating a significant mountain topography.


Oblique convergence resolved in top-southwest stacking structures and coeval orogen-parallel extension giving rise to exhumation of core complexes. Structural setting during exhumation: Coeval activity of strike-slip and normal faults. Upper left: Simplified map of Eastern Desert Basement west of Quseir. Upper right: Folding of western Molasse-type sediments. Lower left: NW extensional shear. Lower right: Schematic profiles drown in SW-NE (upper block) and NW-SE (lower block) direction.


Timing of rock exhumation and sequence of magmatic intrusions along strike of the Neoproterozoic orogen in the Eastern Desert of Egypt. Left: Schematic evolutionary diagram. Right: Summary of cooling ages from basement complexes (red). Basement complexes from north to south are Meatiq, Sibai and Hafafit, orange are molasse sediments, green are cover nappes (undivided)

Selected publications.

For further papers see publications

Neoproterozoic tectonothermal evolution of the Central Eastern Desert, Egypt: a slow velocity tectonic process of core complex exhumation
Harald Fritz, David R. Dallmeyer , Eckart Wallbrecher , J├╝rgen Loizenbauer, Georg Hoinkes, Peter Neumayr, Ali A. Khudeir.- Journal of African Earth Sciences 34 (2002) 137–155.


Structural geology, single zircon ages and fluid inclusion studies of the Meatiq metamorphic core complex: Implications for Neoproterozoic tectonics in the Eastern Desert of Egypt,
J. Loizenbauer, E. Wallbrecher, H. Fritz , P. Neumayr, A.A. Khudeir, U. Kloetzli.- Precambrian Research 110 (2001) 357–383

 

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