Magma Origin and Evolution of Tengchong Cenozoic Volcanic Rocks from West Yunnan,China:Evidence from Whole Rock Geochemistry and Nd-Sr-Pb Isotopes

Tengchong Cenozoic volcanics that have record key information on the tectonic evolution and mantle features of the southeast margin of the Tibetan Plateau are of great importance because of its unique eruption history spanning the entire Quaternary period.Magma origin and evolution of Tengchong Cenozoic volcanic rocks were studied on the basis of Nd-Sr-Pb isotope and major and trace element data from different eruptions in the Ma’anshan area.Different samples within one eruption show relative identical lithologies,chemical and isotopic compositions.However,the geochemical features for the five eruptions are distinct from each other.These volcanic rocks show low Mg# values(<45),moderate to high fractionation of LREEs and HREEs,and enrichment of Pb and Ba and depletion of Nb.Tengchong Cenozoic volcanic rocks were derived from an enriched mantle based on Nd-Sr-Pb isotopic studies.And lines of evidence show that crustal contamination should be involved before the eruption of different periods of Tengchong Cenozoic volcanic rocks. Older subducted components may be responsible for adakite recycling at various stages of evolution, which results in the origin of the enriched mantle source magma accounting for the isotopic features of Tengchong Cenozoic volcanic rocks.Segregated primitive magma pulsating injected into magma chamber,fractional crystallized and contaminated with crust component.Finally,magmas with distinct chemical and isotopic compositions for each eruption formed.The extension of the northeast segment of the Yingjiang tectonic belt triggered the pulsating eruption of the Cenozoic volcanics in the Tengchong area.