Combined apatite fission track and (U脙脙脙脙脙脙Th)/He thermochronometry in a slowly cooled terrane: results from a 3440-m-deep drill hole in the southern Canadian Shield
- 作者：Lorencak ; M. ; Kohn ; B.P. ; Osadetz ; K.G. ; Gleadow ; A.J.W.
- 关键词：apatite ; fission track analysis ; (U脙脙脙脙脙脙Th)/He thermochronometry ; thermal history ; Sudbury Igneous Complex ; Canadian Shield
- 刊名：Earth and Planetary Science Letters
- 出版年：2004
- 期刊代码：18_0012821x
- 类别：ph
- 出版时间：October 30, 2004
- 卷：227
- 期：1-2
- 页码：87-104
- 文件大小：994 K
摘要
Combined apatite fission track (AFT) and (U芒芒芒Th)/He (AHe) thermochronometry can be particularly valuable for deciphering the low temperature thermal history of slowly cooled terranes, especially in those parts where Phanerozoic structural or stratigraphic geological history constraints are absent. We evaluate the results of such a combined approach through the study of 19 samples from a range of lithologies (e.g., granophyre, quartz gabbro, norite) over different depths in a 3440-m-deep drill hole in the 1.85 Ga Sudbury Igneous Complex (SIC), southern Canadian Shield. AFT ages range from 芒芒芒360 Ma at the surface to 芒芒芒140 Ma at the base of the well, with the age芒芒芒depth profile following a sinuous form. This shape is largely attributed to variability in the fission track retentivity due to changing apatite chlorine content between the different lithologies. In contrast, AHe ages range from 芒芒芒210 Ma at a depth of 600 m to 芒芒芒20 Ma at 2800 m and generally show a steady decrease of age with depth. The most consistent and reproducible AHe results are obtained from the relatively low U and Th apatites in mafic rock types. Due to the strict geometrical constraints imposed by the vertical profile, forward modeling of data derived from both methods provides a well-constrained Phanerozoic thermal history. The models reveal a history of heating and cooling during two cycles in Late Silurian to Early Devonian and Permian to Jurassic time, which are attributed mainly to burial beneath foreland sediments derived from the Appalachian Orogen to the southeast and their subsequent erosion. Below 芒芒芒1000 m, AHe samples also record a 芒芒芒weak芒芒芒 Late Cretaceous芒芒芒Early Tertiary heating event not recorded by AHe data from near-surface samples or AFT samples at all. The combined results provide complementary insights into the lowest part of the thermal history, which would not have been recognised using either method alone.