40Ar/39Ar age of Mendanha Alkaline Intrusion, Rio de Janeiro, Brazil

Abstract

The Mendanha Alkaline Intrusion is one of many alkaline occurences of the Southeastern Brazil Alkaline Province. It comprises plutonic rocks (alkali-syenites and syenites) and hypabyssal types (trachytes and ignibrites). In this work is presented new 40 Ar/ 39 Ar ages for this massif. The last reported ages were about 74 My and 65 My by K/Ar method published in 1988. The obtained results show ages of about 64 My (64.12 ± 0.40, 64.04 ± 0.42) e 58 My (58.55 ± 0.45, 57.95 ± 0.69), which are correlated to neighbour magmatic intrusions.