【摘要】 广东省从化市石岭方钠石正长岩是南岭地区已知惟一的早白垩世硅酸不饱和碱性岩。岩石由方钠石、霞石、钙-钠角闪石、霓石-普通辉石、铁黑云母和条纹长石组成,不含独立相斜长石,是一种超溶线碱性正长岩,侵入于佛冈黑云母花岗岩中(γ₅^2（3）),侵位年龄为144.9±5.7Ma（Rb-Sr矿物-全岩等时线）。岩石富含大离子亲石元素Rb,高场强元素REE、Nb、Ta、Zr、U、Th和挥发组分Cl(4355×10^-6～6525×10^-6)、F(2415×10^-6～3525×10^-6)等。在原始地幔标准化微量元素蛛网图上显示Sr、Ba、P、Ti强烈亏损,而Nb、Ta、Zr、Ce强烈富集的特征,具有A型岩套中A₁亚型岩石的微量元素特征。在（Na₂O+K₂O）-SiO₂,（FeO^*/MgO）-SiO₂,（Zr+Nb+Ce+Y）-FeO^*/MgO和（Zr+Nb+Ce+Y）-（Na₂O+K₂O）/CaO等图解中均落入A型岩套分布区。在Y/Nb-Yb/Ta,Y/Nb-Ce/Nb,Nb-Y-Ce和Nb-Y-3Ga图解中均落入A₁亚型区域,并具有OIB亲缘性,表明是深部幔源成因。在锶、钕同位素成分方面,具有低的I_Sr值（0.7060±0.0015）和接近于零的ε_Nd（t）值（-0.15～-0.20）,低的钕模式年龄(T_2DM=0.96Ga),表明岩浆可能起源于上地幔（具全硅酸盐地球BSE端元成分）。说明在早白垩世,南岭地区应力作用已转入拉张为主,大规模拉张作用,造成岩石圈减薄,有利于碱性岩?更多还原

【Abstract】 The Shiling sodalite syenite, Guangdong province, is only early Cretaceous SiO2-undersaturated alkali syenite known in Nanling area, southeastern China. The rock mainly consists of sodalite, nepheline, Ca-Na amphibole, aegirine-augite, annite and perthite. Lack of separate phase of plagioclase indicates that it is a hy-persolvus alkali syenite. The syenite intruded into the Fogang biotite granitoids (γ52(3)), with a dating age of 144. 9 Ma (Rb-Sr whole rock-mineral isochron method). The rock is highly enriched in LILE and HFSE elements such as Rb, Nb, Ta, Zr, Ce, etc. , with the trace element characteristics for Al-subtype rocks of A-type rock suites. In diagrams of Na2O+K2O-SiO2, FeO /MgO-SiO2, (Zr + Nb + Ce + Y)-FeO/MgO and (Zr + Nb+Ce + Y)-(Na2O+K2O)/CaO, the data for the rock are all plotted in the field of A-type granite, evidently distinguishable from fractionated I- and S-type granites. In the diagrams of Y/Nb-Yb/Ta, Y/Nb-Ce/Nb, Nb-Y-Ce and Nb-Y-3Ga, the data of the rock are all fallen in Al-subtype field of A-type rock suites (by Eby, 1992) , suggesting its affinity for OIB mantle source. In the field of Sr and Nd isotope compositions, the rock has a lower ISr value (0. 7060±0. 0015),and a εNd(t) value closing to zero ( - 0. 15--0. 20), and very younger Nd model age of T2DM(0. 96 Ga). These indicate the magma giving formation of the sodalite syenite may be derived from the upper mantle, suggesting that the large-scale lithospheric extension started from early Cretaceous in the Nanling area of southeastern China, and resulted in the formation of alkali syenite.更多还原