Models for the magmatic and tectonic evolution of the late Mesozoic Lhasa Terrane remain controversial. This study presents new zircon U-Pb age and Hf isotopic, whole-rock major and trace element, and Sr-Nd isotopic data for silicic igneous rocks within the Shiquanhe and Guchang areas. The Shiquanhe rhyolites yield zircon U-Pb ages of ca. 148 Ma, which are consistent with the 144 Ma age of the Guchang granites. All of these silicic igneous rocks are peraluminous, high-K calc-alkaline, and have negative ε_Hf(t) and ε_Nd(t) values and low (⁸⁷Sr/⁸⁶Sr)t values. These characteristics are indicative of derivation from magmas formed by the partial melting of ancient crustal metagraywackes. Combining our new data with the results of previous research suggests that a Late Jurassic–Early Cretaceous (165–135 Ma) magmatic belt is present along the Shiquan River–Nam Tso mélange zone within northern Tibet. These rocks collectively record the magmatic evolution from forearc to continental arc settings during the initial southward subduction of the Slainajap Ocean. Our results provide critical constraints on the tectonic evolution of the Slainajap Ocean and the tectono-magmatic evolution of the Lhasa Terrane.