Abstract: Elashan volcanic rocks from late Triassic Elashan Group in southeastern margin of the Qaidam Basin are mainly consisted of a set of medium and acid volcanics combination,including rhyolite and dacite primarily,followed by andesites.The results of the analyses on principal elements,rare-earth elements and trace elements show that Rittman index(δ) of the samples are all below 4,and belongs to calc-alkaline volcanic rocks;the average of SiO₂ is 71.95%,most of the samples have a characteristic of low aluminum,alkali content is higher,and that belongs to the sub-alkaline volcanic rocks.The ratios between LREE and HREE are large and negative Eu anomalies are obvious,so they have the typical late rare earth fractionation characteristics of magmatic differentiation.The samples display a characteristic of LREE enrichment.The discriminant diagram of tectonic environment shows its environment is volcanic arc-within plate volcanic region.This feature may reflect this volcanic activity happened in the tectonic environment of Qinling orogenic belt underthrusting to Qaidam block.