摘要
我国东南沿海江苏、安徽东部、浙江、福建和广东诸省广泛分布新生代玄武岩。本文主要从岩石化学角度,阐述新生代各时期玄武岩的类型和成分,及其在时间上和空间上的演变。分布概况新生代玄武岩分为早第三纪、晚第三纪和第四纪三个时期。
Cenozoic basalts are widely scattered in a zone lying about 350 kin.in width which is near the coast line in Southeastern Provinces of China.They may be divided into the early Tertiary,the late Tertiary,and the Quaternary basalts respectively.Among the three cycles of basalts eruptions,the late Tertiary one is the most widespread.It is now known that in a given region only one cycle of basalts occurs generally,but in rare cases two cyclic basalts may be found together.In each cycle,the"alkalinity"of basalts tends to increase progressively.For example,the earlier members of the early Tertiary period are olivine basalts,gave place to alkali clivine basalts in the later stage;similarly,the basalts of the late Tertiary and the Quarternary periods vary from tholeiite and olivine tholeiite to alkali olivine basalt and basanite.On the whole,they form a mixed but predominantly alkaline basaltic province.Based upon the mineralogical and petrochemical characteristics,the tholeiite is referred to the continental type and to the pigeonite series,in which the ferro basalt and pyroxene anorthosite are enclosed as inclusions.The ferro basalt is considered to be the end product of magmatic differentiation,while the pyroxene anorthosite might originate from earlier crystal accumulation in the magma reservoir.Most of the alkali olivine basalts belong to the soda-series,but some lesser members occurring in late stages tend to be enriched in potash.The alkali olivine basalts often display a series of regular changes in petrochemical and mineralogical properties due to fractional crystallization and contamination.Besides,tholeiite basalts occur only close to the seacoast,whereas in the inland areas,only alkali basalts are found.It is thus postulated that the successively increased depths of the magma chambers,as well as the depth of fracture zones might be due to the plate movement.As to the sequence of eruption,the tholeiitic basalts appear to erupt prior to the alkaline ones.
作者
周新民
陈图华
Zhou Xinmin;Chen Tuhua(Department of Geology,Nanjing University)
出处
《地质学报》
1981年第1期29-40,共12页
Acta Geologica Sinica
