鞍山3.3Ga陈台沟花岗岩地球化学和Nd、Pb同位素特征

Geochemistry and Nd, Pb Isotopic Characteristics of 3.3 Ga Chentaigou Granite in Anshan Area

地球化学和Ｎｄ、Ｐｂ同位素研究表明，鞍山地区陈台沟花岗岩不是早期古老陆壳物质壳内再循环的产物，而是同时代亏损地幔提取物（变玄武质岩石）在短时间内发生再次熔融的结果，形成过程中受到古老陆壳物质的混合混染。３．１５±Ｇａ是鞍山地区地质演化过程的一个重要阶段，它使陈台沟花岗岩的长石Ｐｂ和全岩Ｐｂ发生再次均匀化。３．３Ｇａ的花岗质岩石在鞍山弓长岭地区也有分布，它们来自于与陈台沟花岗岩类似的物源区，但形成条件可能并不完全相同。

Chentaigou intrusion of 3.3 Ga occurs in Chentaigou-Beijiafen area, Anshan city, Liaoning province. It consists of medium to fine(grained granite and prophyritic granite plotting mainly in granitic area in An_Ab_Or diagram, with REE model of high LREE/HREE ratio.Eight samples can not give precise Sm-Nd isochron age, but most of them (six samples) have t DM varying between 3.23 Ga and 3.39 Ga and ε Nd (3.3) between 1.34 and 4.22, with average t DM of 3.31 Ga and ε Nd (3.3) of 2.7 respectively. Nine feldspar samples give a 3.17±0.29 Ga Pb-Pb isochron with initial Pb isotopic compositions 206 Pb/ 204 Pb =13.105, 207 Pb/ 204 Pb =14.972 and μ=9.56. The geochemical and isotopic results are not consistent with the recycle of older continental crust such as 3.8Ga Beijiafen granite in the area, but show that it was formed as a result of remelting of basaltic material (similar to the amphibolite of 3.3Ga Chentaigou supracrustal in composition) derived from depleted mantle source at that time, with somewhat influence of more ancient continental material.It depicts the continuous growth process of the continental crust in the early stage of the earth evolution. The age of 3.17Ga recorded an important geological event happened in Anshan area, which caused re_equilibrium of feldspar lead and whole_rock lead of the Chentaigou granite. Some 3.3 Ga granitic rocks have also been found in Gongchangling area, around 40 km east of the Anshan city. They might come from the same source region as that of the Chentaigou granite, but were probably formed under different physiochemical conditions.