Late Cretaceous adakitic rocks from the western Tibetan Plateau: implications for the subduction of the Neo-Tethys Ocean

Abstract

ABSTRACT It is still hotly debated whether the subduction of the Indus-Yarlung Zangbo Tethyan oceanic lithosphere led to Cretaceous magmatism in the north Lhasa terrane or not. Here, we provide new data on adakitic dacite in the Rutog area, western Tibetan Plateau. Zircon U-Pb dating and Lu-Hf analyses yielded a weighted-mean 206Pb/238U age of ca. 97 Ma for a dacite sample, and corresponding positive zircon εHf(t) values of +5.3 to +10.1. All samples have high Sr (796–1091ppm), but low Y (10.4–11.9 ppm) and Yb (0.68–0.79 ppm) contents, with pronounced high Sr/Y (72.5–97.6) ratios. Furthermore, they have low K2O (1.11–1.49 wt.%) and Th (4.18–4.54 ppm) contents, and low K2O/Na2O (0.18–0.28) and Th/La (0.22–0.24) ratios. These geochemical features are most simialr to those of adakite derived from partial melting of subducted oceanic slab. These new data, in combination with regional geology, enable us to suggest that the Late Cretaceous arc-affinity magmatic rocks were probably triggered by northward subduction of the Indus-Yarlung Zangbo oceanic lithosphere. This will give new insights into the geodynamic evolution of the Indus-Yarlung Zangbo Neo-Tethys Ocean.