东南沿海地区新生代火山作用和地幔柱

Cenozoic Volcanism and Mantle Plume along Southeast Coast of China

通过本文的研究表明 ,东南沿海地区从沿海→内陆 (牛头山→闽清→明溪 )新生代玄武岩的年龄逐渐变小 ,具有火山链的特征 ;微量元素和 Sr- Nd同位素特征与洋岛玄武岩 (OIB)类似 ;上地幔具有过热状态和扰动的热结构 ;地球物理具有低的 Vs 异常及提供了在该区下面具有地幔柱的 CT模式 ;火山岩具有较高的 3He/4He同位素比值 ,因此提出了研究区下面存在地幔柱。进一步根据火山岩的热动力学参数 ,从沿海→内陆 ,随火山岩年龄变小 ,火山岩的碱性程度逐渐增加 ,岩浆起源的深度逐渐变深 ,局部熔融程度逐渐变小等特征 ,提出了地幔柱的形成是由太平洋板块俯冲诱发 ,地幔柱位于俯冲带上面 ,南海的扩张和新生代火山岩的形成是地幔柱作用的结果 ,并提出地幔柱成因演化模式。

The Cenozoic volcanic rocks in the southeastern coast areas of China becomes gradually younger from coast to inland areas (Niutoushan→Minqing→Mingxi), showing characteristics of volcanic chains. The characteristics of trace elements and Sr-Nd isotope are similar to those of OIB. The upper mantle shows a superthermal state and turbulent thermal structure. Geophysical study discovered a low-V s anomaly and proposed a CT model. Volcanic rocks have relatively high 3He/ 4He ratios. These provide evidence for the existence of mantle plume beneath this area. On the basis of thermodynamic parameters, it is shown that, from coast to inland areas, the alkalinity of volcanic rocks and the formation depth of magmas increases and the degree of partial melting decreases as the age of volcanic rocks decreases. It is thus concluded that the formation of the mantle plume was induced by the subduction of the Pacific plate and that the mantle plume is above the subduction zone. Spreading of the South China Sea and formation of Cenozoic volcanic rocks are produced by mantle plume activity. A genesis model for the mantle plume is put forward in this study.