Late Cretaceous adakites in the eastern segment of the Gangdese Belt, southern Tibet: Products of Neo-Tethyan ridge subduction?

Contrasting views remain exist so far for the nature and geodynamic mechanism of the Late Cretaceous magmatism in the southern Gangdese Belt, southern Tibet. To further constrain the tectonomagmatic evolution of southern Tibet during the Late Cretaceous, we present zircon LA-ICPMS U-Pb data, geochemical and Hf isotopic data for the granitoids from the eastern segment of the southern Gangdese Belt, southern Tibet. New age data indicate that the granitoids were emplaced at 84 similar to 78 Ma. These rocks are characterized by high Al2O3(15.69% similar to 17.65%), low MgO (0.47% similar to 1.24%), very low abundances of compatible elements (Cr = 1.34 x 10(-6) similar to 3.27 x 10(-6) Ni = 0.69 x 10(-6) similar to 3.32 x 10(-6)), high Sr (542 x 10(-6) similar to 774 x 10(-6)) and high Sr/Y ratios (48 similar to 397), similar to those of adakite. The rocks are medium-K calc-alkaline, metaluminous (A/CNK = 0.95 similar to 1.04), and are enriched in LILE, depleted in HFSE, and are heterogeneous in zircon epsilon(Hf)(t) values (+0.2 similar to + 15.1). Some of they show distinct positive Eu anomalies (delta Eu = 1.16 similar to 2.26) and middle REE depletion. The Late Cretaceous adakites are interpreted as the products of partial melting of newly underplated mafic lower crust under hydrous amphibolite facies conditions. Compared with the zonal magmatic flare-up events at about 110Ma documented in the middle-northern Gangdese and at about 50Ma documented in the southern Gangdese, we argue that the Neo-Tethyan ridge subduction is the most probable mechanism to trigger the generation of the widespread zonal magmatism in the southern Gangdese during the Late Cretaceous.