贺兰山北段古元古代S型花岗岩岩石地球化学、锆石U-Pb年代学及其地质意义

发布时间：2018-06-13 01:35

本文选题：S型花岗岩 + 孔兹岩带　；参考：《中南大学学报(自然科学版)》2016年01期

【摘要】：对贺兰山北段似斑状花岗岩进行岩相学、岩石地球化学及锆石U-Pb年代学进行研究,探讨其成因机制及其源岩性质。研究结果表明:似斑状花岗岩具有高物质的量比即n(Al_2O_3)/n(Na_2O+K_2O)(记为A/CNK,为1.18~1.29)、低FeOt和MgO质量分数比即w(FeOt)/w(MgO)(小于10)、低P_2O_5(质量分数为0.15%~0.22%)和高K_2O(质量分数为5.09%~5.86%)的地球化学特征,属于典型的强过铝质S型花岗岩。岩石轻稀土富集,轻重稀土分异明显([w(La)/w(Yb)]N=10.4~153.6),具有明显的Eu负异常(δ(Eu)=0.19~0.49);同时,岩体富集大离子亲石元素(LILE)K和Rb,亏损高场强元素(HFSE)Nb,Ta,Zr,Hf和Ti等。似斑状花岗岩与孔兹岩具有相似的微量和稀土元素地球化学特征,推断其应为孔兹岩部分熔融的产物。较低的w(CaO)/w(Na2O)、较高的w(Rb)/w(Sr)和w(Rb)/w(Ba)暗示孔兹岩的原岩应为泥质岩或是以泥质岩为主的、成熟度较高的沉积岩,反映其当时的沉积环境应为被动大陆边缘,而非活动大陆边缘。似斑状花岗岩LA-ICP-MS锆石U-Pb年龄为(1922±31)Ma,与孔兹岩带内所记录的1.92~1.90Ga期间的岩浆-变质事件相吻合,可能反映了构造体制由碰撞挤压到伸展的转变。
[Abstract]:The petrography, geochemistry and zircon U-Pb chronology of porphyry granitoids in the northern part of Helan Mountain are studied, and the genetic mechanism and source rock properties are discussed. The results show that the porphyry granitoids have the geochemical characteristics of the high volume ratio of Al2O3 / nntit / Na2OK2OD (denoted as A / CNK, 1.18 / 1.29, the low FeOt / MgO / w / MgO / w / t / w / MgO) ratio (less than 10, low P _ 2O _ 5 (mass fraction = 0.15 / 0.2222) and high K2O _ 2O _ 5 (mass fraction = 5.09 / 5.86), respectively. It is a typical strong peraluminous S type granite. The rocks are enriched with light rare earths, and the heavy and heavy rare earths are distinguished obviously ([wi Laan / wi Yb] N 10. 4 + 153.6), with obvious EU negative anomalies (未 ~ (+) EU ~ (1) 0.19 ~ (0.49) ~ 0.49. Meanwhile, the rock bodies are enriched with large ion lithophile elements such as LILEN K and Rb, and the high field strength elements HFSEE, NbSU, Tazhuzhuang, HF and Ti are depleted, and the results show that the rock mass is rich in Lilei K and Rb. The porphyry granitoids have similar geochemical characteristics of trace and rare earth elements to the koltzite, and it is inferred that the porphyry granitoids are the product of partial melting of the porphyry rocks. The lower WGCaOU / WN Na _ 2O, the higher WN RbN / WN Sr) and WN RbN / WN Ba) suggest that the source rocks of the kunzite should be argillaceous rocks or mudstone dominated sedimentary rocks with high maturity, indicating that the sedimentary environment at that time should be passive continental margin, not active continental margin. The LA-ICP-MS zircon U-Pb age of porphyry granitoids is 1922 卤31 Ma, which coincides with the magmatic metamorphic events recorded in the Kongzi belt during the period of 1.92 ~ 1.90 Ga, which may reflect the transition of tectonic system from collision compression to extension.
【作者单位】：中国地质大学资源学院;宁夏地质工程院;
【基金】：国家自然科学基金资助项目(41302065,41102047) 中央高校基本科研业务费专项资金资助项目(CUG120702,CUG120842)~~
【分类号】：P588.121;P597.3

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