AGE OF CRUSTAL MELTING AND LEUKOGRANITE FORMATION FROM U-PB ZIRCON AND MONAZITE DATING IN THE WESTERN HIMALAYA, ZANSKAR, INDIA

New U-Pb data from leucogranites in the High Himalayan slab in the wes tern Himalaya of Zanskar reveal that crustal melting occurred at 21-19 .5 Ma and that anatexis occurred along the Himalaya at least from Kash mir-Zanskar to eastern Nepal at similar to 24-19.5 Ma. High-U monazite s from leucogranitic melt pods in migmatites within the 35-km-wide sil limanite + K-feldspar zone at the deepest structural levels exposed (U masi-la) have U-Pb ages of 20.6-19.5 Ma. Higher-level migmatitic melt pods from Shafat in the Suru valley also contain magmatic monazites wi th U-Pb ages of 20.8 +/- 0.3 Ma. Zircons from the leucogranites contai n an similar to 460 Ma inherited component, as do some Umasi-la monazi tes, showing that the protoliths were at least Ordovician in age.