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    大兴安岭中南段哈力黑坝岩体的年代学、地球化学及其构造拆沉作用

    Geochronology and geochemistry of Haliheiba pluton in the central and southern Great Hinggan Range and its tectonic delamination

      摘要
    • 摘要:
      研究目的 在区域地质调查基础上，本文探讨了大兴安岭中南段哈力黑坝岩体早白垩世花岗岩成岩年代、岩石成因类型、源区性质及地球动力学背景。
      研究方法 本文基于显微镜、XRF和(LA–)ICP–MS等手段对哈力黑坝岩体早白垩世花岗岩进行了岩相学、锆石U–Pb年代学、地球化学及Hf同位素组成研究。
      研究结果 哈力黑坝早白垩世花岗岩主要包括中细粒黑云母花岗岩和细粒斑状黑云母花岗岩，LA–ICP–MS锆石U–Pb定年结果分别为（139.1±0.7）Ma和（138.4±1.0）Ma。岩石主量元素具有高硅（74.09%~77.19%）、富碱（7.92%~8.46%），低CaO（0.35%~1.14%）和低MgO（0.15%~0.47%）的特征，属高钾钙碱性系列；其A/CNK值介于0.95~1.08，为准铝质—弱过铝质岩石。岩石相对富集轻稀土元素，(La/Yb)N=3.69~13.17，稀土配分模式图呈右倾海鸥型，具有较为明显的负铕异常（δEu = 0.11~0.47）。岩石微量元素组成显示岩石富集Rb、U、Th、Zr、Hf等元素，强烈亏损Sr、Ba、Ti、P等元素。岩石具有高正的εHf(t)值（+5.0~+11.2）和年轻的二阶段Hf模式年龄（408~731 Ma）。
      结论 哈力黑坝岩体早白垩世花岗岩为铝质A型花岗岩，其源区主要为年轻地壳物质，并有老地壳物质的贡献，形成于伸展的大地构造背景，受控于岩石圈拆沉减薄过程。

       

      Abstract:
      This paper is the result of geological survey engineering.
      Objective The diagenetic age, petrogenetic types, source properties and geodynamic background of the Early Cretaceous granites of Haliheba pluton in the central and southern part of Great Hinggan Range are discussed based on the regional geological survey.
      Methods The lithography of granite, U–Pb chronology, geochemistry and Hf isotope composition of zircon are studied by means of microscope, XRF and (LA–) ICP–MS.
      Results The Early Cretaceous granites in Haliheiba are composed of fine to medium–grained biotite granite and fine–grained porphyritic biotite granite, and zircon U–Pb ages are (139.1±0.7) Ma and (138.4±1.0) Ma, respectively. The granites are characterized by high SiO2 (74.09%−77.19%) and alkali enrichment (7.92%−8.46%), and belong to high–K calc–alkaline series. The A/CNK values range from 0.95 to 1.08, indicating that they are metaluminous to weakly peraluminous rocks. The chrondrite–normalized REE patterns are characterized by enrichment of LREEs with (La/Yb)N values varying from 3.69 to 13.17 and by prominent negative Eu anomalies with δEu values ranging from 0.11 to 0.47. The granites show the enrichment of Rb, U, Th , Nb, Ta, Zr and Hf, and the depletion of Sr, Ba, Ti and P. Zircon Hf isotopic compositions suggest that these granites have high positive εHf(t) values (+5.0 − +11.2) and fairly young two–stage Hf model ages (408−731 Ma).
      Conclusions The Haliheiba granites are aluminous A–type granites, which were mainly derived from partial melting of the juvenile crustal materials associated with ancient crustal materials under extensional tectonic setting that was probably controlled by lithospheric delamination and thinning.

       

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