江苏盘石山玄武岩中橄榄岩包体的氧同位素和微量元素地球化学

Oxygen isotope and trace element compositions of peridotite xenoliths from Panshishan volcano,SE China.Acta Petrologica

本文研究了8个来自江苏盘石山新生代碱性玄武岩中的橄榄岩包体,利用 ICP-MS 技术测定了橄榄岩中单斜辉石的微量元素组成;利用激光氟化技术系统地分析了橄榄石、单斜辉石和斜方辉石的氧同位素比值。结果显示,盘石山橄榄岩包体矿物的氧同位素比值落在“正常”地幔矿物的氧同位素变化范围之内,而且矿物之间达到了氧同位素平衡。部分单斜辉石不相容元素富集的特征表明,有些样品经历了隐性地幔交代作用(cryptical metasomatism),配合氧同位素的数据来看,影响盘石山上地幔的交代介质为来自地幔内部的熔体,不含有地壳组分。从盘石山和安徽女山(盘石山以北约100km)的对比看来,影响女山上地慢的洋壳流体可能来自于华南-华北陆陆碰撞之前的海洋板块俯冲,因此华南-华北的深部缝合带可能就在女山和盘石山之间。

Oxygen isotopic compositions and trace element contents of minerals from 8 peridotite xenoliths hosted by Cenozoic basalts in Panshishan, SE China have been obtained by laser fluorination method and ICP-MS respectively. 81So values of peridotie minerals fall into the range of “normal” mantle minerals, and isotopic equilibrium have been achieved among coexisitng minerals. Elevated incompatible element （U, Nb, Ta, LREE ） contents of elinopyroxenes demonstrate that some Panshishan samples have undergone cryptical metasomatism. Combined with oxygen isotopic data, it is suggested that the metaomatic agent was melt originated within the mantle without involvement of crustal component. The previous studies have shown that the peridotites from Nushan, 100km north of Panshishan, have undergone metasomatism induced by fluid/meh with crustal component from paleo-subduction before the collision between South China and North China blocks at Triassic. Therefore, the deep boudary between South China and North China blocks is suggested to be just between Nushan and Panshishan.