Rb-Sr and U—Pb isotope studies of granitoid plutons in the Göteborg region, southwestern Sweden
1987; Taylor & Francis; Volume: 109; Issue: 1 Linguagem: Inglês
10.1080/11035898709454738
ISSN0016-786X
AutoresEric Welin, Lennart Samuelsson,
Tópico(s)Geochemistry and Geologic Mapping
ResumoAbstract Rb-Sr whole-rock and U-Pb zircon isotopic data from three different granitic plutons in the Göteborg area give ages between 1200 and 1650 Ma. The oldest Lerum granite has a Rb-Sr age of 1611 ± 28 (2sd) Ma and a zircon age of 1603 ± 40 (2sd) Ma. The habits and internal structures of the zircons indicate a metamorphic disturbance which has not, or only sligthly, affected their age since the low initial 87Sr/86Sr 0.7023 ± 0.0008 ratio implies that the maximum age of the granite cannot significantly exceed 1611 Ma. The calculated ages for the Askim granite are 1293 Ma (Rb-Sr whole-rock, MSWD 10.45) and 1362 ± 9 Ma (zircon). The zircon age is assumed to date the age of the crystallization of the granite, while the Rb-Sr age is regarded as a reference age and may reflect the influence of the Sveconor-wegian metamorphism. The Bunketorp granite is formed by mobilization and recrystallization of an older, foliated and felsic Ra granite. The field observations indicate that the Askim granite is younger than the foliated Ra granite. The zircon age of the Bunketorp granite is 1279 ± 62 Ma and the Rb-Sr whole-rock reference age is 1192 Ma. The ages may correspond to local formation of leucosomes in the Askim granite. The initial 87Sr/86Sr ratio 0.7332 of the Bunketorp granite is extremely high in accordance with an anatectic origin of the granite. Key Words: SwedenLerumAskimBunketorpzirconRb-SrU-Pbage determinations
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