摘要
南苏鲁中国大陆科学钻探主孔CCSD-MH及地表的榴辉岩Sm-Nd同位素年龄测试结果显示,每件样品中全岩(Wr)与石榴石(Grt)和绿辉石(Omp)点均在一条直线上。除样品B210R186以外,其余5件榴辉岩均给出十分相近的Sm-Nd等时线年龄,位于202.6~219Ma之间,这与榴辉岩围岩——片麻岩锆石边缘记录的近等温减压退变质年龄(200~220Ma)十分接近,表明测试的榴辉岩中石榴石的Sm-Nd同位素体系有可能在近等温减压退变质时重置,并在向角闪岩相退变质过渡时封闭。因此,笔者测定的202.6~219Ma的Sm-Nd全岩-矿物等时线年龄,应代表了南苏鲁榴辉岩在构造折返过程中近等温减压阶段的退变质年龄,而不能代表苏鲁地体的超高压变质年龄。
Sm-Nd ages of from eclogites in the mainhole of the Chinese Continental Scientific Drilling (CCSD) Project and outcrops in the southern ultrahigh-pressure terrane were determined. The data points of whole rock, garnet and omphacite of each sample all plot on a line. Except for sample B210R186, the other five samples eclogites give very close Sm-Nd isochron ages, ranging between 202.6 and 219 Ma. These Sm-Nd ages are similar to those (SHRIMP U-Pb ages 200 - 220 Ma) of zircon retrogressive rims from the country rock--gneisses, suggesting that the Sm-Nd isotope system of garnet in eclogites analyzed in the study might be reset during the isothermal decompressional retrogressive stage and close during the retrograde transition to amphibolite facies. Therefore the Sm-Nd whole rock-mineral isochron ages of 202.6-219 Ma determined in this paper should be interpreted as representing the retrograde ages of the isothermal decompressional retrogressive stage during exhumation of the South Sulu eclogite, rather than the ultrahigh-pressure metamorphic ages of the Sulu terrane.