Characteristics and tectonic setting of volcanic rocks of the Paleogene Nading Co Formation in the Biluo Co area on the northern margin of the southern Qiangtang block, northern Tibet, China

Volcanic rocks of the Paleogene Nading Co Formation in the Biluo Co on the northern margin of the southern Qiangtang block, northern Tibet, consist of gray latite, dark gray latite, dark gray amygdaloidal olivine basalt and crypto-latite. The geochemical composition of the latite is characterized by SiO2=60.80-61.83%, Al2O3=16.30-17.22%, Na2O/K2O>1 and MgO=0.49-1.42%. The volcanic rocks are LREE-enriched with ∑Ce/∑Y=8.20-9.60 and show weak negative Eu anomalies with δEu=0.70-0.91. These petrological and geochemical characteristics suggest that the volcanic rocks in the study area formed in an intraplate rift environment. The magma of the volcanic rocks was probably derived from partial melting of the materials in the crust-mantle transition zone and related to deep extensional faults. The volcanic rocks have a K-Ar age of 32.60 Ma. According to this age, the geologic age of the volcanic rocks may be determined to be Paleogene.