黔东南宰便辉绿岩锆石U-Pb年代学和地球化学研究

贵州省黔东南州从江县宰便镇镁铁质侵入岩体(辉绿岩)位于扬子陆块与华南褶皱系过渡带上的江南造山带西南段。宰便辉绿岩主量元素研究表明该岩体属于钙碱性系列,以贫K2O(0.03%～0.29%)为特征;微量元素中稀土总量较高,呈现轻稀土富集,没有明显的Eu、Ce异常;LILE(K、Ba、Rb)相对MORB高出数十倍,与板内玄武岩一致;HFSE呈现中至弱的Nb亏损。Sr-Nd同位素研究表明,其87Sr/86Sr变化范围为0.711097～0.712008,具有较高的Isr(t=848Ma,0.710947～0.711726);143Nd/144Nd的变化范围为0.512413～0.512546,εNd(848Ma)具较低的正值(+0.3～+2.3)。锆石U-Pb加权平均年龄为848±15Ma,MSWD=0.54,形成于新元古代中期。锆石U-Pb年龄、Sr-Nd同位素组成和元素地球化学研究表明,宰便辉绿岩体来源于亏损的软流圈地幔,产于板内拉张环境,属于钙碱质玄武岩系,并在上升侵位过程中受到年轻地壳物质不同程度的混染,为导致新元古代Rodinia超大陆裂解的地幔柱活动的产物。本文的研究结果支持华南位于澳大利亚和劳伦大陆之间的Rodinia超大陆重建模式。

Geochemistry and zircon U-Pb age of the Zaibian diabase, Southeast Guizhou Province, China

The Zaibian mafic intrusion is located in the transition zone of the Yangtze Block and the South China fold system,where is the southwest of Jiangnan orogenic belt.The major elements results show that the samples belong to the calc-alkaline series,with the feature of poor K2O(0.03%~0.29%).The REE results of the samples show that the samples enrich LREE,with a higher total REE,and a weak or no Eu and Ce anomaly.The LILE(K,Ba,Rb) is tens times higher than MORB relatively,which is consistent with the intra-plate basalt;the HFSE is mid to weak of Nb.Sr-Nd isotopic studies show that the values of 87Sr/86Sr and 143Nd/144Nd range from 0.711097 to 0.712008,with a high Isr(t= 848Ma,from 0.710947 to 0.711726) and from 0.512413 to 0.512546,with εNd(848Ma) from +0.3 to +2.3),respectively.Zircon U-Pb age is 848 ± 15Ma,MSWD = 0.54,which indicating that the diabase was formed in the mid-Neoproterozoic.U-Pb zircon age,Sr-Nd isotopic compositions and geochemical studies have shown that the diabase was sourced from the depleted asthenospheric mantle,produced in the intra-plate extensional environment,belongs to the calc-alkaline basalt series,contaminated by the crustal material,and formed from the mantle plume,which made the Neoproterozoic supercontinent Rodinia breakup.This study supports the view that South China was located in the supercontinent Rodinia between the continents Australia and Laurentia in the Neoproterozoic.