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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 |
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| Authors: | Eric Welin Matti Vaasjoki Veli Suominen |
| Institution: | a Eric Welin, Laboratoriet for isotopgeologi, Naturhistoriska riksmuseet, S-10405, Stockholm, Sweden b Matti Vaasjoki and Veli Suominen, Geological Survey of Finland, SF-02150, Espoo 15, Finland |
| 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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