Intracratonic Palaeoproterozoic granitoids in northern

• Main Author: Revealed Nd Isotopes
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Key words; granit; Hetta; Nilipää; Tohmo; Fennoscandian; karelia*; karelian; Northern Finland; Lapland
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.514.4251; http://www.geologinenseura.fi/bulletin/Volume79/Ahtonen_etal_2007.pdf

Zircons from twelve Palaeoproterozoic granitoids from the Central Lapland Granitoid Complex (CLGC) and from the Hetta Complex (HC) in northern Finland were dated us-ing the NORDSIM ion microprobe. In addition, U-Pb age determinations on zircons from two samples were made using TIMS. Results reveal a wide range of U-Pb ages from 2.13 Ga to 1.76 Ga. The oldest samples include the porphyritic, weakly deformed Nilipää gran-ite, which has an ion probe concordia age of 2126 ± 5 Ma, compatible with the previous-ly published TIMS age of 2136 ± 5 Ma. The Tohmo granodiorite provided a slightly young-er ion microprobe age of 2105 ± 4 Ma. The age of these two granitoids overlaps the dep-ositional age of Karelian cratonic metasediments, suggesting that they represent an unusual tectonic setting for granitoid magmatism in the Fennoscandian Shield. The Ruoppapalo granodiorite, which is also porphyritic and weakly deformed, yielded an ion probe zircon concordia age of 1905 ± 5 Ma, in accord with the conventional TIMS re-sult. The strongly deformed Molkoköngäs granite has an ion probe concordia age of 1855 ±13 Ma, which is within error limits the same as the TIMS age, 1843 ± 23 Ma. The Pernu