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高校地质学报 ›› 2020, Vol. 26 ›› Issue (2): 132-.DOI: 10.16108/j.issn1006-7493.2019031

• 矿床.岩石.矿物.地球化学 • 上一篇    下一篇

大别山造山带新县二长花岗岩体地球化学与岩石成因

杨春玥,何俊,杨一增,陈福坤   

  1. 中国科学技术大学地球和空间科学学院,合肥 230026
  • 收稿日期:2019-04-05 修回日期:2019-05-20 出版日期:2020-04-20 发布日期:2020-04-29

Geochemical Characteristics and Petrogenesis of Monzogranites from the Xinxian Batholith, Dabie Orogenic Belt

YANG Chunyue,HE Jun,YANG Yizeng,CHEN Fukun   

  1. School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China
  • Received:2019-04-05 Revised:2019-05-20 Online:2020-04-20 Published:2020-04-29

摘要: 大别造山带位于华北板块与扬子板块交界,出露众多中生代中酸性岩体。文章选取新县花岗岩体为研究对象,通过详细的野外地质调查、锆石U-Pb 同位素定年,以及元素和同位素地球化学测试,研究其地质和地球化学组成特征。结果表明,新县岩体主体为二长花岗岩,按照其结晶粒度可分为三个岩石单元,形成于133~129 Ma 之间,并保存有古元古代继承锆石。岩石具有富硅和富碱特征,属于(弱) 过铝质高钾钙碱性系列,亏损Ba、Sr 等大离子亲石元素和P、Ti 等高场强元素,无显著的Nb-Ta 亏损。在稀土元素配分模式图中,具有富集轻稀土、亏损中稀土、弱富集重稀土元素等特征,并具有明显的Eu 负异常,表明岩浆源区可能为角闪石稳定区域,而非加厚下地壳的石榴子石稳定区,推测岩浆形成于加厚地壳的伸展减薄环境。其全岩εNd(t)值为-20.8~-18.4,二阶段模式年龄值为2.61~2.43 Ga,表明岩浆源区主要由古老的地壳物质构成,如崆岭群和陡岭群。对比新县岩体与邻区千鹅冲、宝安寨等Mo 矿床赋矿岩石可以看出,两者具有相似的地球化学组成特征,暗示着存在密切的成因联系,或属于同源岩浆不同演化阶段的产物。

关键词: 大别造山带, 新县二长花岗岩, 岩石成因, 锆石U-Pb年龄, 地球化学

Abstract: The Mesozoic intermediate-acid plutons are widespread within the Dabie orogenic belt which is located between the North China Block and the Yangtze Block. This work conducts an integrated study including field geology, zircon U-Pb dating, and elemental and isotopic measurements for the Xinxian batholith, aiming to reveal its geological and geochemical characteristics and to discuss its petrogenesis. The investigation results indicate that the Xinxian pluton consists predominantly of monzogranites. They were crystallized in 133-129 Ma and can be divided into three units based on grain sizes. Paleoproterozoic inherited zircons have been observed from samples of this pluton. The monzogranites are characterized by enrichment of silica and alkaline, depletion in LILEs (e.g., Ba and Sr) and HFSEs (e.g., P and Ti) with indistinct Nb-Ta anomalies on the primitive-mantle normalized spidergrams, and can be grouped into weakly peraluminous high-K calc-alkaline series. The chondrite-normalized REE patterns show strongly enrichment in LREEs, depletion in MREEs, weakly enrichment in HREEs and exhibit distinct negative Eu anomaly. These features indicate that the monzogranites were derived from an amphibole stable zone in an extensional environment of the thickened crust, rather than from a garnet stable zone in the thickened lower crust. The whole-rock εNd(t) values of this pluton range from -20.8 to -18.4, with two-stage Nd model ages of 2.61 to 2.43 Ga, implying that the parent magmas were originated mainly from partial melting of ancient crustal rocks, such as the Kongling and/ or Douling Groups. By comparison the Xinxian monzogranites with the ore-bearing rocks from the Qian’echong and Baoanzhai Mo deposits, it is shown that they have consistent geochemical features, implying that they have closely genetic relationship, and were likely produced from different differentiation stages of the same magma.

Key words: Dabie Orogenic Belt, the Xinxian monzogranite, petrogenesis, zircon U-Pb age, geochemistry

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