Thermotectonic history of the Trans-Himalayan Ladakh Batholith in the Kargil area, N. W. India, is inferred from new age data obtained here in conjunction with previously published ages. Fission-track (FT) ages on apatite fall around 20±2 Ma recording cooling through temperatures of ∼100°C and indicating an unroofing of 4 km of the Ladakh Range since the Early Miocene. Coexisting apatite and zircon FT ages from two samples in Kargil show the rocks to have cooled at an average rate of 5–6°C/Ma in the past 40 Ma. Zircon FT ages together with mica K−Ar cooling ages from the Ladakh Batholith cluster around 40–50 Ma, probably indicating an Eocene phase of uplift and erosion that affected the bulk of the batholith after the continental collision of India with the Ladakh arc at 55 Ma. Components of the granitoids in Upper Eocene-Lower Oligocene sediments of the Indus Molasse in Ladakh supports this idea. Three hornblende K−Ar ages of 90 Ma, 55 Ma, and 35 Ma are also reported; these distinctly different ages probably reflect cooling through 500–550°C of three phases of I-type plutonism in Ladakh also evidenced by other available radiometric data: 102 Ma (mid-Cretaceous), 60 Ma (Palaeocene), and 40 Ma (Late Eocene); the last phase being localised sheet injections. The geodynamic implications of the age data for the India-Asia collision are discussed.

The cooling and tectonic history of the Higher Himalayan Crystallines (HHC) in southwest Zanskar (along the Kishtwar-Padam traverse) is constrained by K-Ar biotite and fission-track (FT) apatite and zircon ages. A total of nine biotite samples yields ages in the range of 14–24 Ma, indicating the post-metamorphic cooling of these rocks through ∼ 300°C in the Miocene. Overall, the ages become younger away from the Zanskar Shear Zone (ZSZ), which marks the basement-cover detachment fault between the HHC and the Tethyan sedimentary zone, towards the core of the HHC. The same pattern is also observed for the FT apatite ages, which record the cooling of the rocks through ∼ 120°C. The apatite ages range from 11 Ma in the vicinity of the ZSZ to 4 Ma at the granitic core of the HHC. This pattern of discordant cooling ages across the HHC in southwest Zanskar reveals an inversion of isotherms due to fast uplift-denudation (hence cooling) of the HHC core, which is, in turn, related to domal uplift within the HHC. The Chisoti granite gneiss is the exposed domal structure along the studied traverse. Cooling history of two granite gneisses at the core of the HHC is also quantified with the help of the biotite, zircon and apatite ages; the time-temperatures thus obtained indicate a rapid pulse of cooling at ∼ 6 Ma, related to accelerated uplift-denudation of the HHC core at this time. Long-term denudation rates of 0.5–0.7 mm/yr are estimated for the high-grade rocks of the Higher Himalaya in southwest Zanskar over the past 4.0–5.5 m.yr.

Investigations of aerosol optical and physical characteristics using the application of Ängström formula and second order polynomial fit were carried out from April 2006 to March 2009 at Mohal in the Kullu valley. The measurements of spectral aerosol optical depths (AODs) were conducted using multiwavelength radiometer (MWR). The AOD at 0.5 𝜇 m wavelength on daily basis (mean ± standard deviation) for the entire three-year study period is obtained as 0.24 ± 0.08. Seasonal variations show the highest AOD at 0.5 𝜇 m wavelength with ∼0.34 ± 0.08 during pre-monsoon (April–July), followed by ∼0.26 ± 0.08 during monsoon (August–September), ∼0.21 ± 0.05 during post-monsoon (October–November) and ∼0.20 ± 0.07 during winter (December–March). The seasonal values indicate that the AOD at 0.5 𝜇 m wavelength is decreasing from pre-monsoon to winter with a notable reduction around 41%. The Ängström parameters using least square method is not found appropriate for size distribution particularly when coarse mode aerosols dominate. The coefficients of second order polynomial fit are more appropriate for the discrimination of aerosol size or irrespective to the dominance of either of the aerosols size. The difference in coefficient of polynomial fit is used to get confirmation on the dominant mode during different seasons. Study reveals that about 93%, 72% and 59% of AOD spectra are dominated by a wide range of fine mode fractions or mixture of modes during post-monsoon, winter and monsoon, respectively. On the other hand, during pre-monsoon, 72% of AOD spectra are found to be dominated by coarse mode aerosols.