THE BASEMENT TECTONICS OF ERGUN MASSIF

Ergun massif is a typical representative of the Ergun-Mamyn-Jiagedaqi matching massifs.Its basement is composed of Mesoproterozoic greenstone and associated complex,with the tectonic characteristics of earlier crustal evolution.The greenstone belt is a typical volcanic-sedimentary formation formed by metabasic acid volcanic rocks and partly metasedimentary rocks.The bimodal volcanic rocks are mainly tholeiite,which transforms upward into calc-alkali volcanic rock series.The granitoids are of TTG rock series and adamellite-granite assemblage.The lithogeochemical features of all types of rocks in the granite greenstone massif are very much similar to those of the same types in the Archean granite-greenstone belts abroad and in North China platform.All the characteristics of the greenstone basin in the studied area suggest a likely forming environment of back arc rift type of volcanic-sedimentary basin in continental margin.