黑龙江省呼中地区早寒武世花岗岩构造环境的地球化学研究

Geochemical Research on Tectonic Environment of Early Cambrian Granites in the Huzhong Area of Heilongjiang Province

黑龙江省呼中地区早寒武世花岗岩的岩石类型为二长花岗岩, 依据同源岩浆演化理论划分为 4个侵入期次, 岩石结构表现出一期结构演化序列中由细粒向粗粒的演化趋势。花岗岩的岩石地球化学特征显示w(SiO2 )普遍大于 70%,w(Na2O) /w(K2O) <1, 为钙碱性岩石, 标准矿物中均出现刚玉而未见透辉石, 属S型花岗岩; δ(Eu)一般大于 0 5, 属铕弱亏损, N(87Sr) /N(86Sr) >0 706, 应为区内古老陆壳主体经重熔作用成因。各种岩石地球化学指数均表现出研究区花岗岩与碰撞型花岗岩的特征趋于一致, 可与中国西藏及阿曼同碰撞型花岗岩相对比。碰撞型花岗岩的岩浆活动提供了该区新元古代—早寒武世额尔古纳地块南部大陆边缘陆缘增生的构造动力学信息。

The petrographic type of the Early Cambrian granites in the Huzhong area of Heilongjiang Province, is proved to be monzonitic granite, the Early Cambrian granites are divided into four intrusive periods based on the cognate magma evolution theory,and the rock structures show that the granularity evolutive tendency is from fine grain to coarse grain in the texture. The character of rock geochemistry shows that SiO_2>70%, Na_2O/K_2O <1,and the rocks attribute calcic-alkalic rocks, corindon occurs and diopside does not occur in the standard minerals, the rocks attribute granites of S type;δ(Eu)>0.5 shows the rocks belong to weak depletion on Eu,^(87)Sr/^(86)Sr>0.706 indicates the Early Cambrian granites were fomed by the old crust melting.Various of rock geochemical indexes show that the rock's geochemical characteristics are the same as collision granites, and the Early Cambrian granites conform to collision granites of Tibet and Oman. The magmatic activity of collision granites provides the information about the tectonic dynamics from the continental margin epicontinental of the south of Erguna block in the Neo-proterozoic to Early Cambrian.