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±3.4Ma and 855.8±7.0Ma, respectively. Zircon rims from the granitic gneiss record a metamorphic age of 739.4±4.3Ma. Lu-Hf isotopic analyses on zircon grains with Neoproterozoic ages yield negative ε(t) values from -9.0 to -4.2, and the corresponding two-stage Hf model ages are 1965-2228Ma. 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 850-800Ma; (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.