阿尔金环形山花岗片麻岩同位素年龄及成因研究  

Isotopic age and genesis of the monzogranitic gneiss at the Huanxingshan in middle Altyn Tagh

作　　者：王立社[1] 张巍[2] 段星星[1] 龙晓平 马中平[1] 宋忠宝[1] 孙吉明[1] 

机构地区：[1]中国地质调查局西安地质调查中心,西安710054 [2]西安科技大学管理学院,西安710054 [3]中国科学院广州地球化学研究所,广州510640

出　　处：《岩石学报》2015年第1期119-132,共14页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41103021;41272089);中国地质调查局工作项目(1212011220861)联合资助

摘　　要：阿尔金中段环形山二长花岗片麻岩LA-ICP—MS锆石U—Pb年龄为928±9Ma。岩石SiO2含量为72．26％-74．34％，全碱（Na2O＋K2O）为7．22％-8．32％，Al2O3含量为12．40％-13．51％，含量较高；MgO为0．43％-1．07％，FeO^T为2．09％～2．43％，CaO为1．02％～2．03％，TiO2为0．19％-0．32％，含量较低。岩石FeO^T／MgO比值为2．28—4．87和Al2O3／TiO2比值为40．4～69．0（均小于100）、CaO／Na2O比值为0．46～1．06（大于0．30）、K2O／Na2O比值为2．10—3．43（大于1），富集大离子亲石元素Rb、Th、K及La等，亏损Ba、Ta、Nb、Sr、P、Ti，Th／U比值为5．17～14．7、Zr／Hf比值为30．3～34．3，EREE总量平均为193×10^-6，（La／，Yb）N为3．89～5．00（小于10），δEu〈0．5，这些均显示S型花岗岩地球化学特征。低Sr／Ba比值（0．12-0．2）和低的Mg^#值（平均值36．2），具有负Eu异常，显示其源岩区与泥质岩、基性岩的关系不大；0．4〈C／FM值（0．46．64）〈0．8和1．8〈A／FM值（2．09-3．22）〈4的地球化学特征，表明源岩为杂砂岩。锆石饱和温度计和锆石Ti温度计演算结果显示锆石的结晶温度分别为781～801℃（平均789℃）和752—985℃（平均803℃）。估算二长花岗片麻岩源区的压力为0．8～1．6GPa。岩石地球化学特征及其同位素研究表明，新元古代早期的青白157纪阿尔金地区处于同碰撞汇聚作用构造地质背景之下，导致地壳杂砂岩部分熔融形成岩浆，之后上侵结晶形成环形山岩体。The LA-ICP-MS zircon U-Pb isotopic dating on the Huanxingshan monzogranitic gneiss from the middle Ahyn Tagh reveals a U-Pb mean age of 928 ± 9Ma, which approximately represents the intrusive age of the granitic. Geochemical characteristics of major elements exhibit the granite with high Si02 （ 72. 26% - 74. 34% ）, Na2O ＋ K2O （ 7.22% - 8. 32% ） and Al2O3 （ 12.40% - 13.51% ） contents, and low MgO （ 0.43 % - 1.07 % ）, FeOT （ 2. 09% - 2. 43 % ）, CaO （ 1.02% - 2.03 % ） and TiO2 （ 0. 19% - 0. 32% ） contents. FeO^T/MgO （2. 28 - 4. 87 ） and Al2O3/TiO2 （40.4 - 69.0） ratios are less than 100, while CaO/Na2O （ 0. 46 - 1.06） and K2O/Na2O （2. 10 - 3.43） ratios are more than 0. 3 and 1, respectively. These characteristics are similar to values of typical S-type granite. Th/U and Zr/Hf are 5.17 - 14. 7, 30. 3 - 34. 3. Additionally, the granitic gneisses are characterized by relative enrichment in Rb, Th, K, La, and depletion in Ba, Ta, Nb, Sr, P and Ti, which indicate monzogranitic gneiss may be product of Partial melting of sedimentary rocks. All the samples are slightly enriched in LREE with （La/Yb） N ratios ranging from 3.89 to 5.00 （less than 10）. In the chondrite normalized REE patterns, all the granitic gneiss show clear negative Eu abnormalies （δEu 〈 0. 5 ）. These characteristics suggest the rock is S-type granite. Their low Mg^# （ 36. 2, in average）, Sr/Ba （0. 12 - 0. 20） ratios and Eu depletion indicate that the primary magma was derived from partial melting of greywacke rather than muddy rock and basic rock, under temperature of ca. 789 - 803℃ and pressure 0. 8 - 1.6GPa- Based on all above element and isotope geochemistry, it is reasonably suggested that the Huanxingshan granite in Ahyn Tagh was formed in a syn-collision tectonic setting at Early Neoproterozoic era.

关 键 词：同位素年代学 地球化学 二长花岗片麻岩 阿尔金 

分 类 号：P588.121[天文地球—岩石学] P597.3[天文地球—地质学]