Characteristics Of The Weather Station Of The Late Alkali Liquid Lava Flows In The Changbaishan Tianchi Volcano And Its Causes

The alkaline rhyolitic lava flow at Qixiangzhan Stage in Tianchi volcano, Changbaishan area lies to the north of Mount Tianwengfeng and is produced by a parasitic volcanic eruption on the northern slope of Tianchi volano. Now it is not clear on its deposit characteristics, eruptive stage and mechanics. Through the researches of field volcanic geology, and petrography, mineralogy and geochemistry of the rocks from the lava flow at the Late Qixiangzhan Stage, it is concluded as follows:1. The eastern profile at the Late Qixiangzhan Stage shows that the bottom is agglomeratic breccia and over it there is a comenditic lava unit. The bottom and top of the lava unit is the surface facies of obsidian comendite, and the middle part belongs to the comenditic interior facies with the alternation between the dense thick layers and the crumbly thin layers. The rocks from the lava unit have porphyritic and glomeroporphyritic textures and from surface to interior facies, the vitreous texture, spherulite texture and felsitic texture in the matrix can be observed in turn.2. The phenocrysts are sodian sanidine. hedenbergite, fayalite and a little quartz and arfvedsonite pervasively occur in the matix of felsitic interior facies. The mineral sequence of crystallization from early to late is ilmenite. hedenbergite. fayalite. sodian sanidine, quartz and arfvedsonite.3. The alkaline rhyolitic lava at Late Qixiangzhan Stage belongs to comendites of alkaline series, and its compositon is similar to the Tianwenfeng comenditic pumice. The low values of Ba, Sr and Eu maybe show that the magma experiences fractional crystallization.4. The Qixiangzhan parasitic volcano probably experiences explosive eruption and lava flow eruption.