Lithogeochemistry of volcanic rocks and hosted melt inclusions in Wudalianchi, Heilongjiang, China

Abstract

Wudalianchi (五大连池) volcanoes are famous Quaternary ones with fairly good volcanic landscape in Northeast China. The volcanic rocks are phonotephrite, tephri-phonolite, trachyandesite, and basaltic trachyandesite with SiO2 contents of 47.3 wt.%–54.2 wt.%. The characteristic of high K2O content in Wudalianchi volcanic rocks suggests that they probably share a common potassic magma source. The magma evolutions of Wudalianchi volcanic rocks are similar, while the new eruption products of Laoheishan (老黑山) and Huoshaoshan (火烧山) volcanoes are slightly more evolved than the old eruption materials, i.e., the magma of the new eruptions in 1719–1721 from the above two volcanoes is the evolved magma in underground chamber. The main phenocrysts of Wudalianchi volcanic rocks are olivines, clinopyroxenes, and some characteristic K-rich leucites. The various-shaped melt inclusions are found in olivine phenocrysts from new eruption products of Laoheishan and Huoshaoshan volcanoes. By electron microprobe (EMP) analyzing, the contents of SiO2 and total alkali show a wide range, suggesting that the pre-eruptive magma was probably more complicated, or the melt inclusions were rather unhomogeneous. On the basis of EMP results, it is believed that the sulfur degassing rate from this new eruption was much higher than that of the millennium eruption of Tianchi (天池) volcano, while the chlorine degassing rate was a magnitude lower than that of Tianchi volcano.