Meso Cenozoic volcanic rocks widely distributed on Livingston Island are part of the South Shetland magmatic arc.Early to Late Cretaceous volcanism is particularly well represented,but the magmatism also includes Early Tertiary plutonic tonalite and Holocene volcanic rocks. Eight representative lava and dolerite,as well as tonalite samples were analyzed for Sr,Nd,Pb isotope study.The isotopic composition and other geochemical characteristics of rocks,such as the relationship of 87 Sr/ 86 Sr vs 1/Sr,Rb,K and SiO 2,combining with the published and new petrographical and petrochemical data,indicate that the magmatic rocks outcropped on different locations in Livingston Island should be from different magma resources with distinguishable isotope features.Therefore multiple magma generation processes of the volcanism in Livingston Island have been suggested. The Late Cretaceous volcanic rocks from Byers Peninsula and Cape Shirreff,the dolerite at Siddons Point,and the Tertiary tonalite at Barnard Point are all charactered of relatively low 87 Sr/ 86 Sr ratios(≤0.7040) and positive ε Nd ,showing a syngenetic mantlederived magma feature.By contrast,rocks from the central Livingston Island and Hannah Point have significantly higher 87 Sr/ 86 Sr ratios(≥0.7050),implying a possible contamination process.All of the rocks analyzed are distributed within the mantle array in Sr Nd isotopic space, but data for the low Sr ratio group cluster close to primitive mantle values,whereas the high Sr ratio group did not.The primitive compositions of the Quaternary olivine basalt suggests direct derivation from a deep level,primary magma. Studies on the La/Sm La and Ce/Yb Ce pairs of incompatible elements further provide that the formation of above rocks was due to different magma resources by different partial melting degrees.The primary magma of the volcanic rocks from Byers Peninsula,Cape Shirreff,and Siddons Point would be generated by partial melting of upper mantle material in a deeper magma chamber and was directly erupted onto surface.Conversely,the rocks in central Livingston and Hannah Point might be undergone contamination process when the derived magma had to stay in a shallow chamber.The possible crustal source("contamination")could be the Early Triassic Miers Bluff Formation,the basement of Livingston Island,which is a sequence of continental derived metasedimentary rocks deposited in a submarine fan environment.The Pliocene to Recent volcanism is closely related to the extension of Bransfield Strait and the primary magma was directly derived from the upper mantle by partial melting.
