2012

News Registration Abstract submission Deadlines Excursions Accommodation Organizing committee
First circular Second circular Abstracts Seminar History Program Travel Contact us
Новости
Первый циркуляр
Второй циркуляр
Регистрация
Оформление тезисов
Тезисы
Программа
Участники
Размещение
Экскурсии
Проезд
Важные даты
Оргкомитет
Обратная связь

Тезисы международной конференции

Рудный потенциал щелочного, кимберлитового

 и карбонатитового магматизма

Abstracts of International conference

Ore potential of alkaline, kimberlite

and carbonatite magmatism

Petrogenesis of Abu Khruq  Nepheline Syenites,

South Eastern Desert, Egypt

By: Hussein A. Hegazy

Geology Department – Assiut University, Egypt.

E.mail: hegazy 512000@yahoo.com

Mobile: +201227831604

 

The Petrogenesis of Abu Khruq Ring complex rocks which are composed of early uralitized alkaline gabbros and both silica over and, more common, under saturated nepheline syenites have been studied. The Abu Khruq ring complex (ARC) about 85km from the Red Sea is one of several alkaline anorogenic magmatism in Egypt. It belongs to the youngest group of phanerozoic ring complex having an age of 89±2Ma (Serecsists et.al., 1981; Lutz et.al., 1988) and is related to structural lineament trending N30W parallel to the Red SEA.

Field investigation revealed that the (ARC) present as a steeply conical hill, rising up to 874 m.a.s.l. and emplaced into the Late-Proterozoic gneisses and schists. The mass is divided into a central core (about 3 km in diameter) of nepheline syenite dissected by rhyolite and trachyte plugs and an outer discontinuous periphery of syenite and quartz syenite. The coexistence of plutonic and volcanic textures reveal a subvolcanic setting of the ARC. The older intrusive gabbros were emplaced in irregular masses beneath the volcanics, syenites were then emplaced in several incomplete rings decreasing in age toward the center. Early syenites are oversaturated to saturated while the more common latest syenite are undersaturated.

The field relationships as well as the petrographic and chemical characteristics of the ARC reflect the co- magmatic nature of the entire suite. The chemical data support a model in which a mantel – derived alkaline mafic magma was emplaced at a lower crustal level by piecemeal stoping through a collapsed central block  and then extensively fractionated to give an evolved syenitic liquid. The incompatible trace elements (e.g. Nb, Zr, Ce) show enrichment trends with silica increase, consistent with fractional crystallization. Moreover, the low Cr-content in gabbros are consistent with their derivation from an evolved mafic magma. Overall, the compatible trace elements show sharp decreases from gabbros to syenites.

     Open – system crustal contamination provide a mechanism for nepheline syenite to evolve across the feldspar join and become oversaturated. This relation is consistent with the formation of co-genetic silica over and undersaturated syenites from a critically undersaturated magma by both crustal contamination and fractionation processes. This provide important insight into the processes that occur in subvolcanic complexes in continental settings.