Abstract:The Kaladawan area at eastern part of the Altyn Tagh Mountain is tectonically situated between the NE-trending Altyn Tagh strike-slip fault and the W-E-trending Northern Altyn Tagh margin fault.In the area,there appears a set of volcanic-sedimentary rocks.A geochemical study has been made on the basic-intermediate volcanic rocks.The results show two REE patterns: slight LREE-enrichment pattern and a partly flat pattern,indicating an island-arc origin.The Zr /Nb,Nb / Ta and Zr /Hf values indicates that the volcanic rocks have withstood a contamination with the crustal materials.The La-La / Sm diagram of the volcanic rocks displays a coexistence of partial melting and fractional crystallization.In the Hf-Tu-Ta and FeO-Na₂O + K₂O-Mg diagrams,it can be seen that the volcanic rocks of the study area belong to tholeiite-series volcanic-arc basalts.It is suggested that the volcanic rocks were formed in an island-arc environment in the upper wall of subduction zone in the early Paleozoic,with the basalts mainly derived from the mantle.