The Early Cretaceous granodiorites in the Aweng Co area, Tibet: Evidence for the subduction of the Bangong Co-Nujiang River oceanic crust to the south

This paper reports zircon U-Pb data of major and trace elements for the granodiorites from the Aweng Co area in northern Lhasa block. Zircon LA-ICP-MS U-Pb dating of granodiorite yielded an age of 163.3 ±1.7 Ma, suggesting that the intruded rocks were formed in late Early Cretaceous period. Geochemical studies show that Aweng Co granodiorites have typical geochemical characteristics similar to the magnesian andesite/diorite (MA). They are characterized by high Mg^# values (45.42~54.29) and low TFeO^*/MgO ratios (1.58~2.26). They are enriched in LREE in the chondrite-normalized REE patterns, and are enriched in large ion lithophile elements (LILEs) and depleted in high field strength elements (HFSEs). Geochemical features of the Aweng Co magnesian granodiorites are considered to have been generated by the southward subduction of Bangong Co-Nujiang River oceanic lithosphere, and can be genetically regarded as resulting from partial melting of dewatered and subducted oceanic crust melts, which had been metasomatized by mantle peridotite under the condition of oceanic crust subduction. These results provide direct petrologic evidence of the intruded rocks for the southward subduction of the Bangong Co-Nujiang River Ocean.