摘要
细碧-角斑岩属于富钠质的(部分富钾质的)火山岩系。它生成在特定的构造环境中,又与一些铁,铜矿产有成因上的联系,所以一向受到广大地质工作者的重视。近年来,关于细碧-角斑岩的研究报道较多,对其成因的论述也较广。笔者以川西南乡城-得荣一带细碧-角斑岩为例,讨论一下它的岩石学和岩石化学特征,以及有关的火山岩系与板块消减的关系。
Spilite,keratophyre and quartz keratophyre of Permian and Triassic age are found along both the western and eastern sides of the Jinsha River Depth Fracture in the Xiangcheng-Derong area.They often occur together with volcanics of other composition,clastics,radiolarian rocks,etc.Spilitc on the western side of the fracture is often associated with ophiolite suite or ophiolitic melange.Albite-oligoclase and chlorite are the main components of the spilite,but some plagioclase of more basic composition might occur in the keratophyre and quartz keratophyre.Pillow structure,vesicular structure and amygdaloidal structure aren’t seldom seen in the spilite,which may exhibit subophitic,variolitic and glassy textures.The typical variolitic and cedarleaf textures seen in this area are generally thought to have been formed in submarine environment.Besides,subophitic,hyalopilitic and vitrophyric textures are common in the subophitic and glassy facies.The keratophyre and quartz keratophyre appear mainly to be of blastoporphyritic texture but occasionally sphaerolitic texture can be found in the matrix.According to Zavarisky’s petrochemical classification,the spilite,keratophyre and quartz keratophyre in this area belong for the most part to normal series while a few of them should be peraluminous rocks,Alkali-fekdspar is one of the predominent rock-forming minerals.Except for the only potassic spilite,Na_(2)O occupies a higher percentage of the whole alkalies of the spilite-keratophyre.Ferromagnesian components vary greatly in the rocks,but magnesian oxides are generally richer than ironxides.The spilite-keratophyre in this area are rather typical petrochemically when compared with those in well-investigated areas abroad and at home.The spilite-keratophyre are higher in Na_(2)O(generally,Na_(2)O 3%)and volatile component,and lower in K_(2)O in comparision with rocks of the normal series.Contents of Mg,Fe,Ca and Al seem somewhat lower in the spilite than in common basic rocks.From an analysis of silica index and potash index of the volcanics,including the spilite,keratophyre and quartz keratophyre,in this area,oceanic crust are thought to be subdueted from west to east during the Permian,Early-Middle Triassic and Late Triassic at a convergence rate of 5.2,6.1 and 6.2 cm/yr,respectively.Considering that both primary and secondary features could be seen in the spilite-keratophyre in this and other areas,that spilite-keratophyre might be classified into either normal or peraluminous series,either calc-alkaline or sub-alkaline series,either alkaline or nonalkaline series and either calc-alkaline or tholeiite series according to different authors,and that spilite-keratophyre might be interpreted to originate from upper mantle material at great depth or by anatectic melting of crustal substance on the basis of ratioτ,the authors are of the idea that spilite-keratophyre are polygenetic,i.e.,they might be either of primary origin from spilitic magma or derived by autometamorphism,autohydrothermal metasomatism or some other secondary,diagenetic or metamorphic processes.
作者
张之孟
王忠实
郑裕民
Zhang Zhimeng;Wang Zhongshi;Zheng Yumin(Institute of Geology,Chinese Academy of Geological Sciences;Geological Survey Team,Sichuan Bureau of Geology)
出处
《地质学报》
1981年第3期179-194,共16页
Acta Geologica Sinica
