%0 Journal Article
%T Isotopic ages of Lentiira 每 Kuhmo 每 Kostomuksha olivine lamproite - Group II kimberlites
%A Hugh O＊Brien
%A Dave Phillips
%A Roy Spencer
%J Bulletin of the Geological Society of Finland
%D 2007
%I The Geological Society of Finland
%X The Lentiira-Kuhmo-Kostomuksha triangle, along the Finland 每 Russian border and within the central part of the Archean Karelian craton, contains numerous examples of phlogopiterich, ultramafic, mantle-xenocryst-bearing and, in some cases, diamond-bearing dike rocks.Laser probe Ar-Ar data on phlogopite from 3 dike rocks on the Finnish side (Lentiira, Kuhmo) all gave ages within error of each other, 1202㊣3 Ma (2考), 1199㊣3 Ma (2考) and 1204㊣4 Ma (2考) while a fourth sample produced mixed ages. Published Rb-Sr dates on mineralogically and chemically similar dikes from the Russian side (Kostomuksha) are 1232㊣5 Ma. The question remains open whether these represent two distinct age populations or whether differences in isotopic system behavior are the reason for the 30 m.y. age difference.
%K kimberlite
%K lamproite
%K phlogopite
%K biotite
%K absolute age
%K Ar-40/Ar-39
%K Proterozoic
%K Lentiira
%K Seitaper
%K Kuhmo
%K Finland
%K Kostomuksha
%K Russian Federation
%U http://www.geologinenseura.fi/bulletin/Volume79/OBrien_etal_2007.pdf