南桥高度亏损N-MORB的发现及其地质意义

The discovery of Nanqiao highly depleted N-MORB and geological significance

对赣西北九岭古岛弧西延部分的湖南浏阳南桥玄武岩进行了单颗粒锆石蒸发法2 0 7Pb/ 2 0 6Pb年龄测定 ,结果为 12 71± 2Ma。该玄武岩辉绿岩显示高度亏损的地球化学特性 :K2 O极低 ,不相容的高场强元素和稀土元素的丰度均低于 (少数接近 )N_MORB的平均丰度 ,εNd(12 71Ma)为 6 .86～ 8.98,具典型N_MORB特性 ,可能为沿古俯冲带分布的洋壳残片 ,为九岭古岛弧提供了新的证据。

With single-zircon evaporation technique, the authors determined 207Pb/ 206Pb age of Nanqiao basalt in Hunan, which is located along the westward extension of ancient Jiuling island arc in northwest Jiangxi. The data yield a zircon crystallization age of 1?271±2 Ma for the basalt. The basalt and diabase show highly depleted geochemical features: K 2O values are very low, abundances of their incompatible HFSE and REE are mostly lower than those of N-MORB (with a few close to the latter), and ε Nd(1?271 Ma)values vary from 6.86 to 8.98, suggesting typical N-MORB geochemical characteristics. This basalt may represent a relict of the ocean crust distributed along an ancient subduction zone and can serve as new evidence for ancient Jiuling island arc.