40Ar/39Ar geochronology and geochemistry of Pleistocene trachyandesite in Tengchong, western Yunnan, China, and its tectonic implication

Mangbang area is located in the east of Tengchong with widely distribution of the Late Cenozoic volcanoes. 40Ar/39Ar 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.