Mangbang　area　is　located　in　the　east　of　Tengchong　with　widely　distribution　of　the　Late　Cenozoic　volcanoes.　Ar-40/Ar-39　analysis　on　matrix　separate　from　two　trachyandesite　samples　collected　from　the　Mangbang　area　yielded　a　high-precise　plateau　age　of　2.　1　+/-　0.　1Ma　and　2.　0　+/-　0.　1Ma,　indicating　the　effusive　age　as　Early　Pleistocene.　Analyzed　samples　appear　as　high-potassium　calc-alkaline　features,　and　are　enriched　in　large　ion　lithophile　elements　(LILE),　but　depleted　in　high　field　strength　elements　(　HESE),　which　show　the　arc　volcanic　and　intraplate　volcanic　transition　characteristic,　speculating　that　they　may　form　in　post-orogenic　environment.　The　generation　of　Pleistocene　volcanic　rocks　in　the　Tengchong　Block　is　related　to　extension　collapse　after　the　India-Asia　collision　result　in　partial　melting　of　an　enriched　mantle　source.　The　Indosinian　Block　escape　to　the　southeast　and　rejuvenation　of　Tengchong　arcuate　strike-slip　fault　zone　(e.g.,　Longchuanjiang　fault　belt　and　Dayingjiang　fault　belt)　induced　the　volcanic　eruption　and　emplacement.