ZIRCON TYPOLOGY IN THE AIT-OKLAN AND TEG-ORAK GRANITIC MASSIFS (PHARUSIAN TRENCH - HOGGAR)

Boulfelfel, Nour-eddine; Ouabadi, Aziouz; Laouar, Rabah; Abdallah, Nachida; Fezaa, Nassima

Bulletin du Service Géologique de l'Algérie
Volume 15, Numéro 1, Pages 51-62
2004-01-01

Zircon Typology In The Ait-oklan And Teg-orak Granitic Massifs (pharusian Trench - Hoggar)

Authors : Boulfelfel Nour-eddine . Ouabadi Aziouz . Laouar Rabah . Abdallah Nachida . Fezaa Nassima .

Abstract

Typological study of zircons has been developed by Pupin and Turco (1970; 1972) and Pupin (1980). The behaviour of zircon during magma genesis and evolution is very important in that it is a host mineral for several trace elements, such as:Zr, Y, and REE. On the other hand, zircon is commonly used for geochronological studies of granites using the U/Pb method. Modal and geochemical analyses of granitoids as well as typological analysis of biotites can define the geochemical affinity and the geotectonic environment of the granitoids. As a complement, zircon typology is an original method that can precisely define the magmatic affinity of the granitoids and, in many cases, shows the effects of contamination processes during granitoid genesis. The aim of this study is, to describe this method and to test it on the Pan-African granitoids of Ait-Oklan and Teg-Orak, whose magamatic affinity has already been determined by petrologic and geochemical studies. All zircon populations that are present in the Ait-Oklan and Teg-Orak granitoids show sub-types clustering around S20, S25 and P3 to P5 sub-types of the rocks that are characterized by S-type affinity. Comparison between the different zircon populations and their convergence to the order of crystallisation indicates a typological evolution relative to their time of crystallization.The majority of zircons are included in biotite flakes; they are weakly to highly coloured, but limpid varieties can occur in rare occasions. The typological study of zircons confirms the sub-alkaline affinity of the Ait-Oklan and Teg-Orak granitoids.