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Age differences between RbSr whole rock and UPb zircon ages of syn- and postorogenic Svecokarelian granitoids in Sottunga, SW Finland

Authors
Journal
Lithos
0024-4937
Publisher
Elsevier
Publication Date
Volume
16
Issue
4
Identifiers
DOI: 10.1016/0024-4937(83)90017-8

Abstract

Abstract The UPb age on pooled data of zircnos from the postorogenic Svecokarelian Mosshaga granite is 1788 ± 11 Ma (2 σ). The corresponding RbSr whole rock age is 1742 ± 34 Ma (2 σ). The Mosshaga granite intrudes a synorogenic granodiorite, which has a UPb zircon age of 1889 ± 10 Ma and a RbSr whole rock age of 1850 ± 28 Ma. The age differences between the UPb zircon ages and RbSr whole rock ages are concluded to be geologically significant. It is shown that the Mosshaga pluton cooled rapidly and as a consequence the RbSr isotopic system closed at a time very close to the crystallization of the zircons. A commonly observed feldspar and biotite alteration in Svecokarelian granitoids indicates migration of Rb and Sr isotopes in the whole rock system which may lead to apparently younger RbSr ages.

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