摘要:
广东良口亚髻山霞石正长岩岩体内带为霞石角闪正长岩,w(SiO2)平均值60.45%, w(K2O)/w(Na2O)平均值0.97, w(Nb)/w(Ta)平均值22.68, w(Zr)/w(Hf)平均值39.96, w(ΣCe)/w(ΣYb)平均值6.32, δEu(0.30)负异常明显.外带为黑云角闪正长岩,w(SiO2)平均值60.34%, w(K2O)/w(Na2O)平均值1.50, w(Nb)/w(Ta)平均值21.23, w(Zr)/w(Hf)平均值43.07, w(ΣCe)/w(ΣYb)平均值7.85,δEu(0.47)负异常明显.同位素研究显示,岩体形成时间约134.6 ±8.9 Ma(Rb-Sr 同位素测年), ISr平均值0.70675, εNd(t)平均值-2.8,暗示了岩石的源区为上地幔-下地壳重熔型物质,其高碱特征可能与上地幔岩浆分异有关,它形成于白垩纪早期古太平板块俯冲后撤诱发的陆-陆碰撞造山后拉张构造环境,这一过程对华南地区构造演化具有一定重要的地质意义.%The internal zone of nepheline-syenite in Liangkou Yajishan, Guangdong Province is com-posed of amphibole-bearing nepheline-syenite, with SiO2averaging 60.45%, K2O/Na2O averaging 0.97,Nb/Ta averaging 22.68,Zr/Hf averaging 39.96, ΣCe/ΣYb averaging 6.32, and δEu(0.30) .The external zone,Bi-Am-syenites zone, have average SiO2of 60.34%,average K2O/Na2O of 1.50, average Nb/Ta of 21.23,average Zr/Hf of 43.07, average ΣCe/ΣYb of 7.85, and negative anomaly in Eu(δEu=0.47).Isotopic studies show that the rock formation time is about 134.6 ±8.9 Ma(Rb-Sr whole rock isochron method), with average ISrof 0.706 75, average εNd(t)of -2.8.Isotope features suggest that the magmatic rocks were derived from the upper mantle.The intrusive rocks formed at a con-tinent-continent post-collisional extension setting,which was significant to the early Cretaceous tectonic e-volution of the South China Block.