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Table 1: Results of AFT analyses : ages calculated using dosimeter glass IRMM-540R with 15 ppm U, zeta = 250, irradiated at FRMII, calibrated by traditional zeta approach and external detector method for apatite sample SAP, N=Number of grains, ρ – track densities given in 10 = Mean FT ages of cogenetic minerals Average geothermal gradient of the order of 30°C/km has been adopted.
Closure temperatures for apatite and zircon have been adopted 110°C and 240°C respectively.
All the samples were prepared for the external detector method.
AFT mounts were etched with 70% HNO at room temperature for 30 s. Zircons were etched in KOH-Na OH eutectic etchant [36-39] at 215°C on Spinot digital hot plate for ∼8 hrs.
By applying apatite fission track analysis, the possible uplift rate of the Sushina hill was attempted to be revealed, which could be reflected by an offset age of two cogenetic minerals (Table 2).
The sample was placed in 48% HF for 2 hrs to clean up grains.
After etching, mica sheets were firmly attached on the sample mounts.
This high error is most likely due to a very low uranium concentration (0.68 ppm).
As already known, low uranium samples place limits on how robust the ages could be.
The samples for this study were processed in the laboratory of the Geological Survey of India, Kolkata, after obtaining permission from the Director General, GSI, Kolkata, West Bengal.