Neoproterozoic magmatism in eastern Himalayan terrane

Geochronological investigation on gneisses of granitic to leucogranitic compositions in Cuona, south Tibet, reveal that their protoliths formed at 808.8 ± 7.9-816.4 ± 3.4 Ma and 855.8 ± 7.0 Ma, respectively. Zircon rims from the granitic gneiss record a metamorphic age of 739.4 ± 4.3 Ma. Lu-Hf isotopic analyses on zircon grains with Neoproterozoic ages yield negative Hf（t） values from -9.0 to -4.2, and the corre- sponding two-stage Hf model ages are 1965-2228 Ma. Whole-rock geochemical data indicate that all granitic gneisses are K-riched calc-alkali series. These new data together with literature data show that （1） the Himalayan terrane experienced an episode of Neoproterozoic magmatism at 850-800 Ma; （2） the Neoproterozoic magma of granitic compositions were derived from partial melting of ancient crusts, possibly due to the thermal perturbation related with the breakup of the Rodinia supercontinent.