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苏皖地区发育的新生代玄武岩中富含地幔橄榄岩捕虏体 ,测定了 2 5个橄榄岩全岩的锇同位素组成。结果表明大部分样品呈亏损特征 ,1 87Os/ 1 88Os=0 .119～ 0 .12 9. Os同位素比值与主量成分之间有显著的相关性 .采用 1 87Os/ 1 88Os- Al2 O3代用等时线方法 ,由截距得到初始值 (1 87Os/ 1 88Os) 0 =0 .10 9,在对流地幔的 1 87Os/ 1 88Os比值演化线上获得模式年龄 t=2 .5 (±0 .1) Ga,为晚太古 -早元古代。用样品组中最低的锇同位素组成 ,即 1 87Os/ 1 88Os=0 .119,计算 Re亏损模式年龄 ,t=1.2 Ga,为中元古代。表明苏皖地区新生代玄武岩中的地幔橄榄岩捕虏体具有古老的形成年龄 ,它们是经过显生宙减薄作用后的残余地幔的碎片。大陆岩石圈地幔的古老形成年龄与上覆地壳克拉通的古老稳定年龄相耦合。
The Cenozoic basalts developed in the area of Jiangsu and Anhui Province are rich in mantle peridotite xenoliths, and the osmium isotopic compositions of 25 peridotite rocks are determined. The results showed that most of the samples showed a loss characteristic, with a significant correlation between the isotope ratio of 1 87Os / 1 88Os = 0.119 and 0 .12 9. Os isotope ratio of 1 87Os / 1 88Os-Al 2 O 3 Time-line method, the initial value (1 87Os / 1 88Os) 0 = 0.10 9 was obtained from the intercept, and the model age t = 2.5 (± 0.1 ) Ga, for Late Archaean - Early Proterozoic. With the lowest osmium isotope composition in the sample group, ie, 1 87Os / 1 88Os = 0.119, the age of Re depletion model is calculated, t = 1.2 Ga, which is the Mesoproterozoic. It shows that the mantle peridotite xenoliths in the Cenozoic basalts in the Jiangsu-Anhui region have the ancient age of formation. They are the remnants of the residual mantle after the Phanerozoic thinning. The ancient formation age of the continental lithospheric mantle is coupled with the ancient stable age of the overlying crustal craton.