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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 ε_(Hf)(t) values from-9.0 to-4.2,and the corresponding 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.
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 analyzes on zircon grains with Neoproterozoic ages yield negative ε_ (Hf) (t) values from-9.0 to-4.2, and the corresponding 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.