Strontium and oxygen isotope relations and geochemistry of the Abu Khruq Complex, Egypt: implications for petrogenesis of the alkaline rocks of the Eastern Desert, Egypt

Thesis/Dissertation · Mon Jan 01 04:00:00 EST 1979

OSTI ID:5482478

Lutz, T M

The objectives of this thesis were to define the genesis and evolution of alkaline intrusive complexes in the Eastern Desert of Egypt. Systematic analysis of the geology, ages, geochemistry, and strontium and oxygen isotope relations were employed toward these ends. One complex, Gabal Abu Khruq, was studied in detail. The syenitic rocks occur as both undersaturated and oversaturated types, and at Abu Khruq and Nigrub El Fogani both occur together. At most complexes the syenitic rocks with the lowest differentiation indices are peralkaline and close to silica saturation. Isotopic results show that alkaline activity in Egypt has a long history: concordant K-Ar and Rb-Sr ages range from Cambrian to Cretaceous. The ages have a periodicity of about 52 my. The lowest initial /sup 87/Sr//sup 86/Sr ratios at each complex are 0.704 or lower. However, at all complexes some Sr isotopic heterogeneity is apparent. At Abu Khruq petrographic and isotopic evidence suggests that extensive hydrothermal activity accompanied emplacement of the complex. Non-radiogenic Sr derived from the essexite gabbros was added to the nepheline syenites in this stage. A correlation of initial /sup 87/Sr//sup 86/Sr ratio with inverse Sr concentration suggests that roughly the same amount of Sr derived from the country rocks was added to each quartz syenite sample during this event. The low initial /sup 87/Sr//sup 86/Sr ratios and tectonic position of the complexes within the Proterozoic convergent zone in the Arabo-Nubian shield are consistent with possible origin of continental magmas in source regions spatially associated with orogenic environments, as suggested by the general correlation of alkaline rocks and rifts with older orogenic zones.

• Research Organization: Pennsylvania Univ., Philadelphia (USA)
• OSTI ID: 5482478
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580400* -- Geochemistry-- (-1989)
AFRICA
ALKALINE EARTH METALS
ARID LANDS
CHEMISTRY
DESERTS
DEVELOPING COUNTRIES
EGYPTIAN ARAB REPUBLIC
ELEMENTS
GABBROS
GEOCHEMISTRY
IGNEOUS ROCKS
ISOTOPE RATIO
METALS
NONMETALS
ORIGIN
OXYGEN
PETROGRAPHY
PLUTONIC ROCKS
ROCKS
STRONTIUM
SYENITES
TECTONICS