东南沿海地区第四纪大陆岩石圈地幔的特征

东南沿海地区新生代玄武岩中的橄榄岩包体来自年轻的大陆岩石圈地幔 ,该岩石圈地幔在岩石学、矿物组成、痕量元素以及Sr Nd同位素组成等各方面具有很大差异。这些差异反映了它们来自不同的地幔过程。南海张开与地幔热柱有关 ,南海扩张后第四纪形成的火山岩携至地表的包体更多保留了地幔热柱的信息。橄榄岩包体的矿物成分与深海橄榄岩类似 ,相对贫Opx而富Ol;在痕量元素上 ,表现为强不相容元素的富集 ,其配分模式类似于其寄主岩 ;Nd同位素强烈亏损 ,显示出比MORB源区更亏损的特征。大陆岩石圈地幔经历了来自地幔深处的贫SiO2 熔体的进一步改造。

THE MANTLE CHARACTERISTICS OF QUATERNARY CONTINENTAL LITHOSPHERE,SOUTHEAST COAST OF CHINA

The peridotite xenoliths in the Cenozoic basalts came from young lithospheric mantle in the southeastern China. These peridotites contain a great deal of information of deep processes. There are a great number of differences in petrology, mineralogy, trace elements and Sr-Nd isotopic compositions in the peridotite xenoliths. These differences show that these peridotite xenoliths have undergone different mantle processes. The South China Sea spreading is regarded to relate to the mantle plume. The peridotite xenoliths in the Quaternary volcanic rocks after the South China Sea spreading may reserve more information about the mantle plume. The mineral compositions of peridotite xenoliths are similar to the abyssal peridotites. The xenoliths are depleted in Opx and enriched in Ol, and enriched in strongly incompatible elements, which patterns are similar to those of their host rocks. In addition, the xenoliths are more depleted than MORB in Sr-Nd isotopic compositions. The continental lithosphere was subjected to further alteration by the SiO 2-poor melts from the deep mantle.