Sr and Nd isotope geochemistry of Late Triassic volcanic rocks at Gêladaindong in the source region of the Yangtze River and its significance

Abstract： Sr and Nd isotope analysis and zircon U-Pb dating were performed for Late Triassic volcanic rocks in the Gêladaindong area in the source region of the Yangtze River. The zircon U-Pb age is 212±1.7 Ma. The initial Sr isotope ratios of basalt and andesite range from 0.703 25 to 0.709 17 and from 0.70545 to 0.708 44 respectively， the εNd(t) values are negative， ranging from -0.8 to -4.6， and tDM ranges from 1064 to 1 379 Ma， which indicates that the primary magma of the Late Triassic volcanic rocks might be of crust-mantle mixing type. These ages， combined with the related major element， rare earth element and trace element geochemistry， suggest that the formation of this suite of volcanic rocks was related to the island arc-active continental-margin environment.