苏鲁造山带五莲新元古代花岗岩类成因的Sr-Nd同位素证据

五莲新元古代花岗岩类分布于五莲断裂以北, 动力变形强, 但变质程度弱, 仅达到绿片岩相.岩性以黑云正长花岗质为主, 少数为石英正长质.岩石中Sr同位素初始值的变化范围很广, 从0.697 306~0.753 765, 除了部分是由于源区的不均一或多源不同比例混合外, 岩浆侵位过程中或固结后的次生扰动可能也起着一定的作用.而它们的ε_Nd (750 Ma) 均为负值且变化范围广(-3.1~-24.3), Nd同位素二阶段模式年龄从1.7~3.4 Ga, 均显示它们的源区以古老的地壳为主, 但具有多源混合的特征.推测五莲新元古代花岗岩类最可能的成因是太古代的TTG片麻岩(主要是其中的英云闪长质组分) 在压力约0.8 Gpa (相当于~25 km的中下地壳) 条件下发生部分熔融, 并混入了不同比例的年轻地幔来源物质.地幔来源物质的加入对于五莲新元古代花岗岩类的成因有重要的影响. 

Petrogenesis of Neoproterozoic Granitoids from the Wulian Region in the Sulu Orogen: Sr-Nd Isotopic Constraints

The Neoproterozoic granitoids in Wulian region are located north of the Wulian fault. They have undergone strong dynamic deformation but are slightly metamorphosed (green-schist facies). The granitoids are mainly biotite-syenogranitic in composition with minor quartz syenitic. The initial 87Sr/86 Sr ratios (I_Sr) are wide, ranging from 0.697 306 to 0.753 765. This may partially be ascribed to the inhomogeneity of magma source material or multi-source mixing with different proportions. Secondary disturbed after the granitic body's intrusion and concretion may also play a role, to some degree. The ε_Nd (750 Ma) values of the granitoids are all lower than 0 and with wide ranges (-3.1 to-24.3), and the model ages (T_DM) of two stages ranges from 1.7 to 3.4 Ga. This indicates that the parental magma of the Neoproterozoic granitoids in the Wulian region was primarily derived from crustal materials but with the mixed features of multi-sources. Therefore, the Neoproterozoic granitoids in Wulian have most probably been generated by partial melting of Archaean TTG gneisses (major tonalitic component thereinto) at pressures of about 0.8 Gpa (i.e. within the middle or the lower crust), and the addition of different proportions of mantle-derived juvenile materials. The addition of mantle-derived materials has been an important influence on the genesis of the Neoproterozoic granitoids in the Wulian region.