摘要
中国东南沿海中生代火山岩叠置在几个不同的基底构造单元之上,不同单元内的火山岩在锶、钕同位素组成上存在着很大的差异。其中隶属于下扬子亚板块的浙西—赣东北区火山岩的^(87)Sr/^(86)Sr初始值普遍较低,而^(143)Nd/^(144)Nd初始值则较高。华夏亚板块内的火山岩,以武夷山隆起为核心向沿海方向^(143)Nd/^(144)Nd初始值不断增高,而^(87)Sr/^(86)Sr初始值则呈下降趋势。火山岩中的同位素特征及其时空变化规律在很大程度上是其基底变质杂岩中同位素性质的再现。区内中生代酸性岩浆的形成是业已存在的地壳物质再循环的结果。
Mesozoic volcanic rocks along the coastal region of southeastern China were superimposed on different basement tectonic units in the Cathausian and Lower Yangtze subplates. The regional-ization of Mesozoic magmatism was controlled clearly by the relevant units and the characters of metamorphic complexes thereof. The Mesozoic volcanic rocks developed in different basement tectonic units have great difference in Sr and Nd isotopic compositions. The rocks in the Western Zhejiang-northeastern Jiangxi region which belongs to the Lower Yangtze subplate have lower initial 87Sr/86Sr ratios (less than 0. 707) but higher initial Nd isotopic ratios. εNd(t) is -3. 47 on the average. The initial 143 Nd/144 Nd values of the Mesozoic volcanic rocks developed in the Cathaysian subplate increase notably from early to late, and from the core of the Wuyi uplift coastward, the initial 143Nd/144Nd ratios increase constantly, while the initial 87Sr/86Sr values decrease. As an exception, the isotopic features of the volcanic rocks in eastern Zhejiang are similar roughly to those in the Wuyi uplift,that is,they have higher initial 87Sr/86Sr and lower initial 143Nd/144Nd values. The isotope features and their spatial variations in Mesozoic volcanic rocks in the study region are manifestations of the isotope features in basement metamorphic complexes to a great extent,and the crustal retention ages of Nd isotopes in volcanic rocks are far from their emplacement ages,but are close to the retention ages of Nd isotopes in basement metamorphic complexes,which show that the Mesozoic acid magmas in this region mainly resulted from recy-cling of pre-existing crustal materials.
出处
《地质学报》
EI
CAS
CSCD
北大核心
1996年第1期35-47,共13页
Acta Geologica Sinica
基金
国家自然科学基金(编号 49070162)
地质矿产部"七五"攻关项目(编号 86017)联合资助
关键词
锶
钕
同位素
火山岩
岩浆
成因
Sr and Nd isotopic composition, crustal recycling, coastal region of southeastern China
