Fission track dates of Mandi granite and adjacent tectonic units in Kulu–Beas valley, NW Himalaya, India

Abstract

We present zircon fission track (FT) ages from the lower parts of the Higher Himalayan crystalline (HHC) ranging from 3.9 to 4.3 Ma and apatite FT age as 1.9 ± 0.4 Ma . Combined with previous radiometric dates, these ages provide the low temperature data for the area and enable us to draw temperature–time plot which shows significant increase in cooling rates from 25 ∘ C / Ma in Oligocene and 4 ∘ C / Ma in Miocene to about 64 ∘ C / Ma during Pliocene. For the Mandi granite, the zircon FT ages range from 3.9 to 4.9 Ma while apatite FT obtained is 2.8 ± 0.5 Ma . The rapid Pliocene exhumation is characterized by a rapid increase in cooling rates from ∼ 3.4 ∘ C / Ma in Miocene to ∼ 77 ∘ C / Ma after 5.0 Ma. Our results confirm the rapid Pliocene to Pleistocene cooling of rocks of Kulu–Beas valley similar to that of the neighboring units from the frontal parts of HHC.