Isotopic ages of Lentiira - Kuhmo - Kostomuksha olivine lamproite - Group II kimberlites

The Lentiira-Kuhmo-Kostomuksha triangle, along the Finland – Russian border and within the central part of the Archean Karelian craton, contains numerous examples of phlogopite-rich, ultramafic, mantle-xenocryst-bearing and, in some cases, diamond-bearing dike rocks. Laser probe Ar-Ar data on phlogo...

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Bibliographic Details
Published in:Bulletin of the Geological Society of Finland
Main Authors: H. O'Brien, D. Phillips, R. Spencer
Format: Article in Journal/Newspaper
Language:English
Published: Geological Society of Finland 2007
Subjects:
kimberlite
lamproite
phlogopite
biotite
absolute age
Ar-40/Ar-39
Proterozoic
Lentiira
Seitaperä
Kuhmo
Finland
Kostomuksha
Russian Federation
Geology
QE1-996.5
karelia*
karelian
Online Access:https://doi.org/10.17741/bgsf/79.2.004
https://doaj.org/article/537f327cec9f41428e9470302d1e0d11
Description
Summary:The Lentiira-Kuhmo-Kostomuksha triangle, along the Finland – Russian border and within the central part of the Archean Karelian craton, contains numerous examples of phlogopite-rich, 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 (2σ), 1199 ± 3 Ma (2σ) and 1204 ± 4 Ma (2σ) 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.

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