IMPLICATIONS OF APATITE FISSION-TRACK ANALYSIS FOR THE THERMAL HISTORY OF THE SCOTIAN BASIN, OFFSHORE NOVA-SCOTIA, CANADA

Forty apatite samples of sandstone from ten exploration wells in the S cotian Basin, offshore Nova Scotia, Canada, were used for fission trac k analysis and thermal history reconstruction. The sample depths range from 1000 to 5500 m. Fission tracks in all apatite samples are at lea st partially annealed. Apatite fission track ages for the shallowest s amples, from the Logan Canyon Formation, are older than their stratigr aphic ages and therefore retain some record of cooling in the detrital source area. Samples from deeper formations (Missisauga, Mic Mac and Verrill Canyon) have apatite fission track ages younger than their str atigraphic ages (some give zero ages), indicating partial to total ann ealing of fission tracks in apatite. The degree of annealing in most s amples modelled is significantly higher than would be expected given t heir present-day temperatures. This indicates that these samples exper ienced a thermal overprint; they have been hotter in the past than at present. Inverse modelling by a Constrained Random Search (CRS) techni que was carried out on the six best data sets. The results indicate th at strata at depths of 1650-2600 m in the modelled wells were heated t o paleotemperatures of about 80-110 degrees C at some time during the interval 100-40 Ma. The magnitude of the thermal overprint predicted ( estimated) by the modelling ranges from 1 degrees to 55 degrees C amon g the five wells modelled. Zircon fission track data from fifteen samp les in four wells do not constrain burial temperatures. These data ind icate a mixed provenance for the sediments.