西南极利文斯顿岛中部中－新生代火山岩的岩相学和矿物学特征

出露在利文斯顿岛中部的中－晚白垩世火山碎屑岩为多源的角砾凝灰岩、角砾岩和集块碎屑岩，成分以安山质为主。橄榄玄武岩主要在史莱夫角出露，为全晶质斑状构造；主要出露在中利文斯顿和汉那角的安山岩、玄武安山岩多具细晶微斑构造。更新世至现代的火山岩为全晶质斑状的橄榄玄武岩和火山碎屑岩。熔岩的基本矿物组合大致相似，均为斜长石＋辉石（＋橄榄石）＋铁的氧化物，但矿物的含量比例因岩性不同而有所区别。岩石中的斜长石斑晶多具正环带；随着岩石ＳｉＯ２含量的增加，斜长石中Ｏｒ和Ａｂ组分增加而Ａｎ含量下降，斑晶边缘成分一般与基质里长石的成分相近。安山岩和玄武安山岩含有中长石－拉长石斑晶，玄武岩主要含拉长石斑晶，但橄榄玄武岩和粗玄岩中斜长石斑晶的核部为富钙的倍长石。更新世－现代的橄榄玄武岩，其所含斜长石斑晶和基质长石亦比较富钙。玄武安山岩中的辉石多为普通辉石，橄榄玄武岩和玄武岩中含有透辉石斑晶。辉石的Ｔｉ含量低，这是钙碱性火山岩的共同特点。史莱夫角的橄榄玄武岩含有贵橄榄石斑晶。粗玄岩中橄榄石成分与史莱夫角基质橄榄石成分相近。更新世至现代的橄榄玄武岩中既有正常结晶的橄榄石斑晶，还见到高Ｆｏ组分的深源捕掳晶。上述玄武岩中矿物组合的基本特征证明

PETROGRAPHY AND MINERALOGY OF THE MESOZOIC CENOZOIC VOLCANIC ROCKS FROM THE CENTRAL PART OF LIVINGSTON ISLAND,WEST ANTARCTICA

The Middle Late Cretaceous volcanoclastic rocks outcropped on the central part of Livingston Island include heteromict lapilli tuffs,lapillistone and agglomeratic breccias predominantly andesitic in composition.Olivine basalts with holocrystalline porphyritic texture are mainly found in the Shirreff Point.Most basaltic andesite and andesite outcropped in Central Livingston and Hannah Point are finely crystalline with mino microporphyritic texture.The holocrystalline porphyritic olivine basalts and pyroclastic rocks are the components of Pleistocene to recent volcanic activities.On the whole,the mineral association,Plagioclase+pyroxene(+olivine)+iro opaque,is much similar in distinctive lavas,however,the content of minerals is different.The plagioclase phenocrysts are usually with normal zoning,the Or and Ab components increase and An decreases with increasing SiO 2 content of rocks and the composition of the phenocryst margin is almost the same as that of plagioclases in matrix.The predominant phenocrysts of basaltic adnesite and andesite are andesine labradorite,that of basalt is labradorite,whereas the core of plagioclase phenocryst of the olivine basalt from Shirreff Point or the dolerite from Siddons Point is bytownite.The plagioclase in the Pleistocene to recent olivine basalt,either as phenocryst or in matrix,is richer in CaO.The clinopyroxene phenocryst associates with plagioclase forming a porphyritic texture or glomerocryst texture.Augite is mainly found in basaltic andesite and diorite in olivine basalt and basalt,both pyroxene are depleted in Ti.The olivine composition of dolerite is similar to the matrix olivine in the olivine basalt from Sirreff Point,where chrysolite is the major phenocryst.There are two types of olivine phenocrysts in the olivine basalt with Pleistocene to recent age,one was crystallized under a general crystallizing condition and the other was the xenocryst with high Fo content.Above mentioned characteristics of the mineral associations suggested that the volcanic rocks were probably formed by an equilibrium crystallization.The olivine basalt from Shirreff Point has a genetic relationship with the dolerite in Siddons Point as showed by the olivine composition and the high An content of plagioclase,however,differs from the rocks of Central Livingston and Hannah Point.The olivine xenocryst found in the youngest olivine basalt indicates the magma was a primary basaltic magma which was directly derived from a deep magma chamber.