Abstract:

Pb isotopic compositions of basement, granitoids and volcanic rocks in Tibetan Plateau, with a total data sets of 486, were compiled and analyzed. Three different types of main geochemical crustal or mantle geochemical end-members were identified by their Pb characteristics. The first one is the NeoTethyan mantle reservoir represented by Yarlung Zangpo ophiolite, showing low Pb features; the second one is the Himalayan continental crust represented by the basement and granitoids from Tethyan and Higher Himalayas with the most enriched Pb compositions; the third one is the North Tibetan Plateau enriched mantle source region, with a medium enriched Pb compositions. These three end-members classification is very consistent with the former result by Sr-Nd isotopic studies. A detailed discrimination for the rocks from Lhasa block allowed us to separate them into two groups. The first group, including the I-type Gangdese granitoid plutons, Linzizong volcanic rocks and adakitic ore-bearing porphyries, etc., shows strong Tethyan oceanic crust affinity, with significant source contribution of the recycled Tethyan oceanic crust or depleted mantle. The second group, solely represented by the ultrapotassic volcanics found in western Lhasa block, exhibits an obvious input of the Himalayan continental crust to their mantle source regions. In Lhasa block, the main processes of Tethyan subduction and thereafter India-Asia collision were all recorded by Pb isotopic geochemistry in magmatism during different stages. The crust-mantle interaction among the above end-members has played an important role in the evolution and uplift of the Tibetan Plateau.

Key words: Pb isotope, geochemistry, granitoid, volcanic rocks, Tibetan Plateau