Large-scale nappes of the deformed Higher Himalayan Crystallines (HHC) were thrust southward over the Lesser Himalayan Proterozoic foreland during the Late Cenozoic. Critical evaluation of shear fabrics, reveals that the HHC underwent an earlier phase of ductile shearing with top-to-southwest overthrust-type sense of movement. On which was superposed layer-parallel NE-trending extension. As a consequence, the Zanskar Shear Zone (ZSZ) along the northern boundary of the HHC is re-interpreted as a complex ductile shear zone with an initial top-to-southwest sense of thrusting followed by the later superposition of top to northeast-directed extension. This period of extension is recognized across the whole of the HHC and is the result of the uplift and exhumation of the HHC by southwestward directed thrusting and ramping along numerous thrusts including the Main Central Thrust (MCT).
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 tM:ough temperatures of ~ 100~ 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~ in the past 40 Ma. Zircon FT ages together with mica K-At 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 Oiigocene 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~ 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 Ioealised sheet injections. The geodynamic implications of the age data for the India-Asia collision are discussed.
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