2013

SHRIMP U–Pb zircon geochronology: Evidence for emplacement time of some granitoids north Eastern Desert, Egypt

Bataa H. Ali

^*Nuclear Materials Authority, P.O. Box. 530, Cairo, Egypt

In an effort to better understanding of the crystallization ages of some Neopreterozoic granitic plutons, the precise SHRIMP U–Pb zircon geochronology was used. The studied granites comprise G.Abu Marwa, G. El-Glouf. G. Faliqu El-Sahl and Faliqu El-Waar and G. Gattar in the north Eastern Desert of Egypt. The crystallization ages for the studied monzogranites and syenogranites range between 595 to 605 Ma (Abu Marwa, 595± 8.5 Ma, El-Glouf 596.4 ± 11.2 Ma,  Faliqu El Sahl and El Waar 605.1 ± 10 Ma) where as Gattar granites recorded 580 ± 22.2 Ma.

The obtained data revealed the ages of magmatic crystallization as well as the presence of slightly older presumably inherited zircon grains. Xenocrystic zircons are found in most of the younger granitoid samples; the xenocrystic grains are all of Neoproterozoic ages. They fall into three age ranges that correspond to the ages of other Eastern Desert igneous rocks. This study reveals that U–Pb zircon age dating yield a reliable age for low radioactive younger granites. Discordant ages are related to presence of slightly older inherited zircon grains and to the effect of radiation damage which acts as open system in which gain and loss of U and Pb and intermediate radiogenic daughter are common. These older zircons may be entrained from wall rock during late contamination inherited from contributing source materials. These older zircon are corresponding to Late-proterozoic igneous rocks.