摘要
利用岩石化学、地球化学、年代学等方法对福建政和地区火山岩系列进行综合研究，确定其为早古生代的岛弧拉斑玄武岩－钙碱性火山岩组合的岛弧火山岩系，揭示了自浙江龙泉经福建政和、建瓯、南平、将乐、赣南延入广东和平、台山、开平一带存在一条早古生代岛弧火山岩系。结合前人的资料对本区早古生代岛弧的形成和演化作了探讨。
The early Paleozoic volcanic rocks are distributed mainly in Xingxi, Xiongshan,Daoxiang, Tieshan, Dawai, Nanyang etc. near Zhenghe city, Fujian Province. They can be divided into two factes i. e. volcanic elastic rock factes at southeastern part and volcanic lava to super-epicomplex factes at northwestern part.The authors study the ancient volcanic rock series systematically using the methods of petrology, petrochemistry, geochemistry, isotopic geology, isotopic geochronology. In the figures of FeO/MgO-SiO2 and FeO/MgO-FeO the points of this volcanic rock series are located at the boundary and the transitional area of tholeiite basalt series and cafe-alkali volcanic rock series and in the figure of AFM, it is shown that the evolution direction of this volcanic rock series is from tholeiite basalt to cafe-alkali volcanic rock. The REE distribution pattern of andesite basalt is even with a little deficit of Eu just like that of island-arc tholeiite in Japan; for andesite-tuff and andesite the pattern is the type of enriched LREE with a little deficit of Eu and a ratio of LREE/HREE of 3.568. The trace elements of andesite basalt are enriched in Sc, Cr, V, Zn, Ph, Yb, Y, Ce and deficient in Sr, K, Rb, Ba,Nb, Mn, P. The deficit of big ionic lithophile elements indicates that the original magma came from mantle and was slightly mixed with the crust material for the neutral rock of andesite and andesite-tuff, the trace elements are enriched in Rb, Ba,Sc, Cr, V etc. and deficient in Nb, Zr, Ti. These facts may imply that the neutral rock was also slightly mixed with the crust material in the diagenetic process. In the figures of F1-F2, F2-F3 and TiO2-10MnO-10P2O5 the points of this volcanic rock are located in the area of island-arc tholeiite, in the figure of lgτ-lg (σ25×100) the points of this volcanic rock are located in the area of subduction volcanic rock and in the figures of “Y + Nb”-Rb and Yb-La-Nb the points of this volcanic rock are located in the area of island-arc volcanic rock and island-arc tholeiite.These facts all show that this volcanic rock was formed in island-arc zone. The isochronic age of Rb-Sr is 560.8 ± 14 Ma. Through comparing with the volcanic rock developed in adjacent area at same time we can conclude that it was formed at early Paleozoic. These facts prove that there is an early Paleozoic island-arc volcanic zone along Longquan, south-western Zhejiang Province, Zhenghe, Jianao, Nanping, Jiangle, Fujian Province, southern Jiangxi Province and Heping, Taishan,Guangdong Province. This island-arc volcanic rock exsited from Middle Cambrian to Ordovician. Between Silurian and early Devonian the volcanic activity ceased.Along this zone the collision between continents happened and collision orogenic zone was formed During Early to Middle Devonian the molasse was deposited in foreland basin and the collision tended to cease. The discovery of Early Paleozoic island-arc volcanic rock series in northern Fujian Province is very important for the study of the tectonic evolution in southeastern China.
出处
《地质科学》
CAS
CSCD
北大核心
1995年第2期105-116,共12页
Chinese Journal of Geology(Scientia Geologica Sinica)
基金
国家自然科学基金
关键词
早古生代
岛弧
火山岩
拉斑玄
大地构造演化
Northern Fujian Province, Early Paleozoic island-arc, Volcanic rock, Th+ Ca series, Tectonic evolution
