Abstract:

The geochemical characteristics of the lavas in the Yeba Formation in the eastern Gangdise tectonic belt in Tibet show that they are calc-alkali volcanic rocks. The basic volcanic rocks are believed to be originated from partial melting of the mantle that might have undergone fluid metasomatism, and the intermediate-acidic volcanic rocks to be formed by partial melting of the crust. The lavas in the Yeba Formation were formed in an island arc or an active continental margin tectonic environment. It is concluded that northward subduction of the Neo-Tethys resulted in the magmatic eruption of the Yeba Formation in the Early-Middle Jurassic time. The island arc area where the Yeba Formation developed is suggested to be also the most favorable area for important VMS deposits. Meantime, it is proposed that the studies on the lavas in the Yeba Formation are also meaningful to understand the Early Jurassic biotic crisis, climate change, and regression or transgression events.

Key words: Gangdise tectonic belt in Tibet, Yeba Formation lavas, geochemical characteristics, tectonic environment