海南岛屯昌玄武质科马提岩Sm-Nd同位素年龄及其地质意义

SM-ND AGE OF TUNCHANG BASALTIC KOMATIITES AND ITS GEOLOGICAL SIGNIFICANCE IN HAINAN ISLAND

海南岛屯昌玄武质科马提岩成岩时代一直未获解决。作者利用 Sm- Nd同位素法测试了 5件样品 ,获得岩石 Sm- Nd同位素等时线年龄 1 687± 1 0 Ma,及与其相近的 Nd模式年龄 1 637- 1 756Ma。同时获得了钕同位素初始比值 INd=0 .51 0 796± 0 .0 0 0 0 0 6( 2σ) ,εNd( T) =+ 6.64。表明玄武质科马提岩结晶年龄为古元古代 ( 1 687Ma) ,反映了海南岛在古元古时期的壳

The diagenetic age of Tunchang basaltic komatiites in Hainan Island has never been solved for a long time. Five samples of the basaltic komatiites are taken to be measured by Sm Nd radioactive isotope method in this study.The Sm Nd whole rock isochron age of 1687±10Ma with I Nd =0.510796±0.000006(2σ) and ε Nd (T)=+6.64 has been obtained.Meanwhile the basaltic komatiites give Nd model age of 1637-1756 Ma which correspond basically to the isochron age of 1687 Ma.These indicate that Tunchang basaltic komatiites were formed in the Palaeo proterozoic (about 1687Ma) and its primary magmatic would be derived from a depleted mantle .