Abstract: A set of grey-purple layered volcanic rocks are found widely distributed from the mountain flank to the main peak of Daliuchong volcano, but it's difficult to identify whether they are volcaniclastic rock or lava rock just by field investigation and the crystal structure observation under microscope. The study of matrix microstructure of the volcanic rocks can help to identify the volcanic facies. We recognize the eruptive facies rocks through observation of the matrix microstructure and pore shape with comparison to those of the volcanic vent facies, extrusive facies and effusive facies rocks under microscope, thus the mentioned layered volcanic rocks could be named as dacitic crystal fragment tuff. Combining the joint work of field investigation, systematic sampling, chemical analyzing and microscopic observation, we summary the Daliuchong volcanic facies as follows:1. The effusive facies lava constitutes the base of Daliuchong volcano and was produced by early eruption.2. The explosive facies is composed of dacite crystal fragment welded tuff and volcanic breccia and mainly distributes on the W, S and NE flank of the volcanic cone.3. The volcanic conduit with its diameter more than one hundred meters is located about 100 meters south of the main peak of the Daliuchong volcano.4. The extrusive facies rock is only exposed near the peak of Daliuchong volcano.Therefore, the volcanism of Daliuchong volcano can be speculated as:Large-scale lava overflowing occurred in the early eruption period; then explosive eruptions happened; at last, the volcanisms ceased marked with magma extrusion as lava dome and plug.

Key words: Daliuchong volcano, volcanic facies distribution, petrology, microscopic structure

摘要： 云南腾冲大六冲火山上，从山腰大丫口至山顶沿途广泛出露1套青灰色-紫红色的层状火山岩，但仅通过野外肉眼观察难以判定其为火山碎屑岩或是熔岩，而研究火山岩的基质结构可以帮助判断其所属岩相。文中将其基质结构与火山通道相、侵出相及溢流相熔岩的基质结构作对比，并结合与溢流相熔岩气孔形态的比较结果，认为它属于爆发相产物，定名为英安质晶屑熔结凝灰岩。通过对大六冲各火山翼的野外勘查、覆盖式采样及系统的镜下鉴定，区分了各岩相火山岩的野外和显微特征，大致划分了各岩相的分布范围：溢流相应为早期喷发形成的基底，部分区域被爆发相所覆盖；爆发相英安质晶屑熔结凝灰岩和火山角砾岩主要分布在火山西翼、南翼和东北翼；火山通道相位于主峰山顶南侧约100m的位置，直立产出，直径超过100m；侵出相仅在山顶附近有出露。因此，推测大六冲火山早期经历过较大规模的岩浆溢出，时隔多年后又发生爆炸式喷发，最后以岩浆的侵出为标志而停止活动，火山颈因受长期剥蚀而出露。

关键词: 大六冲火山, 岩相分布, 岩石学, 显微结构