Resumen de Combined apatite fission track and (U-Th)/He thermochronometry on a shield: a case study from southern Finland
M. Lorencak, Barry P. Kohn, Andrew J.W. Gleadow, D.X. Belton, J. Woodhead
The potential application of combined apatite fission track (AFT) and (U-Th)/He thermochronometry has been tested on the central Fennoscandian Shield in Finland. AFT analysis has been carried out on 15 samples from a range of lithologies. Apparent AFT ages varyfrom -360 Ma to-1000 Ma, with track length distributions of 10.2-12 mm. Chlorine measurements suggest a correlation between AFT age and Cl content despite relatively low absolute Cl values. Preliminary (U-Th)/He apatite results from granitic rocks are invariably older than their coexisting AFT ages, highlighting the problem of micro-inclusions and/or U and Th zoning.
However, results from gabbroic lithologies yield ages between -300 and 400 Ma, which are younger than their coexisting A FT ages and can be replicated. This suggests that under certain circumstances the (LI- Th)/ He apatite thermochronometry can be applied to cratonic environments, despite recent studies which suggest that it is difficult to reproduce such data from rocks which have experienced slow cooling or resided for a lengthy period in the He partial retention zone.
The combined results suggest a burial of the southern Finland shield under a shallow sedimentaiy cover related to a Caledonian foreland basin, which was thick enough to totally reset the (U-Th)/He apatite system, but only partially affect the AFT signature.
