长白山天池火山气象站期晚期碱流质熔岩的岩石学研究

通过野外火山堆积物的相分析、岩石显微鉴定和造岩矿物化学分析，可以确认气象站期晚期碱流质熔岩是典型的溢流熔浆冷却固结形成的，不是碎成熔岩。熔岩流的顶部和底部是黑曜质碱流岩的表壳相，中部是致密厚层与薄层相间产出的、具有塑性变形的碱流岩的内部相。组成熔岩流的岩石具有斑状和聚斑结构，从表壳相向内部相基质依次发育玻璃质结构、（微）球粒结构和霏细结构。斑晶矿物钠透长石、钙铁辉石、铁橄榄石和少量石英出现在熔岩流的所有岩相中，而钠铁闪石、铁钠透闪石和钛铁矿则作为内部相基质中的显微斑晶出现。气象站期晚期碱流质熔岩是过铝质、过碱性的钠闪碱流质熔岩，属于碱性系列，与意大利潘泰莱里亚岛碱流岩相比，富Si、Al、K、Mg、Ca和P而贫Fe、Na、Mn和Ti。

Petrology of Comenditic Lava from the Eruption at Late Qixiangzhan Stage in Tianchi Volcano, Changbaishan Area

Through the facies analysis of volcanic deposits in the field,the microscopic identification and the rock-forming mineral chemistry,it can be proved that the comenditic lava at Late Qixiangzhan Stage in Tianchi volcano,Changbaishan area,is formed by the overflow but not the clastogenic lava.The top and bottom of the lava flow is the obsidian comendite of surface facies,and the middle part belongs to the comenditic interior facies with the typical plastic deformation and flow bending as well as the alternation between the dense thick layers and the crumbly thin layers.The rocks from the lava flow 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,because of the difference of cooling rate.The phenocrysts,sodian sanidine,hedenbergite,fayalite and a little quartz,appear in all the facies of lava flow,and yet arfvedsonite,ferrorichterite and ilmenite occur as the micro-phenocrysts in the matix of interior facies.In comparison with the peralkaline pantellerite from Pantelleria volcano,Italy,the oversaturated comendites at Late Qixiangzhan Stage are rich in Si,Al,K,Mg,Ca and P,and poor in Fe,Na,Mn and Ti,and belongs to peraluminous alkaline series.