The quaternary eruptive sequence of the Tengchong volcanic group, southwestern China

Abstract

The Tengchong volcanic group in SW China is situated along the NS-oriented tectonic belt in the southeastern margin of the Tibetan plateau. The volcanic field has experienced intense tectonic stress due to the continuous subduction of the Indian plate under the Eurasian plate, and throughout Quaternary has experienced pervasive volcanism. The present volcanic rocks cover the successive domains of basic, intermediate (Group II) and acid (Group I) rocks, belonging to the high-K calc-alkaline series. Correspondingly, the eruption types of the Tengchong volcanoes roughly fall into two categories: explosive eruptions with large amounts of volcaniclastics and lava; and moderately quiet central eruptions with small amounts of scoria and lava overflow.According to systematic geochronological dating methods such as K-Ar, Ar-Ar, 14C AMS, and OSL dating, as well as field work, we separate the eruptive sequence of the Tengchong volcanic group during the Quaternary into four subsequences: the early Pleistocene, middle Pleistocene, late Pleistocene and the Holocene epoch. The early to middle Quaternary eruption sequence consists of a series of explosive eruptions, with almost all the eruptive dacitic volcaniclasts and lava constituting the bottom layer of the Tengchong basin. The Tengchong volcanism reached its climax in the late Pleistocene when it formed numerous cinder cones. A series of moderately quiet central eruptions occurred in the late Quaternary, and basic and intermediate-acid volcanic rocks formed the upper layer of the basin. From this study, three volcanoes are determined to be of Holocene age, and we conclude that the volcanic activity moved from the south and periphery to the north and center, and ended in the Heikongshan eruption ∼ 3600 years ago.