华北克拉通兴城早白垩世玄武玢岩锆石、金红石地球化学特征及其地质意义
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P588.14+6;P595

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国家自然科学基金(91962106);高等学校学科创新引智计划(BP071902);中国地质大学(北京)2019年度本科教育质量提升计划和2020年度创新创业训练计划(202011415006)


Zircon and rutile geochemistry of the Early Cretaceous basaltic porphyry from Xingcheng in the North China Craton and its geodynamic implications
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    摘要:

    华北克拉通在中生代时期发生大规模的岩石圈减薄,伴生的早白垩世火山岩为研究克拉通破坏提供了窗口,但其中镁铁质火山岩成因和岩浆源区性质的争议,制约了对克拉通破坏机制和中生代岩石圈减薄结束时间的认识。本文用激光剥蚀电感耦合等离子质谱(LA-ICP-MS)方法对兴城玄武玢岩中的锆石、金红石进行了系统的微量元素分析,以揭示岩浆源区性质及其演化,并进一步探讨了华北克拉通中生代岩石圈减薄的机制和结束时间。锆石tTi温度计计算结果表明,兴城玄武玢岩锆石结晶温度为695~779℃,平均温度为730℃,说明玄武玢岩可能起源于俯冲带地幔楔交代橄榄岩。微量元素分析结果显示,锆石富集HREE,LREE与HREE分异明显,Nb、Ti亏损,Th、U和Hf相对富集,Ce、Eu呈不同程度的正、负异常;金红石Nb、Ti、Hf等高场强元素呈不同程度富集,Sr明显亏损,无明显的Ce、Eu异常。微量元素特征也显示玄武玢岩岩浆起源于岩石圈地幔交代橄榄岩,后期经历了氧化作用和分离结晶作用。结合区域内相关地质资料,认为兴城玄武玢岩岩浆为古老岛弧型岩浆。华北克拉通中生代岩石圈减薄的结束时间可约束到早白垩世晚期(约105 Ma),高角度俯冲的古太平洋板块回撤为华北克拉通岩石圈减薄的一级动力学机制,热化学侵蚀或拆沉为二级机制。

    Abstract:

    The Mesozoic large-scale lithosphere thinning of North China Craton (NCC) was documented by coeval volcanic rocks. Petrogenesis and magma source of the mafic volcanic rocks in the NCC is debated, which therefore restricts the understanding of mechanism and termination time of the NCC Mesozoic lithosphere thinning. In this paper, the Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) was used to analyze the trace elements of zircons and rutiles in basaltic porphyry from the Xingcheng area, with the purpose of revealing the nature and evolution of magma source and further providing insights into mechanism and termination time of the NCC Mesozoic lithosphere thinning. tTi thermometer of zircon shows that the zircons crystallized at 695~779℃, with an average crystallization temperature at 730℃, indicative of an origin of mantle wedge metasomatic peridotite in the subduction zone. Zircons of basaltic porphyry display geochemical characteristics of high HREE and HREE/LREE ratio, negative Nb-Ti anomalies, relative enrichment of Th, U and Hf, positive Ce anomaly, and negative Eu anomaly. Rutile granules are characterized by high concentrations of Nb, Ti and Hf, and Pb, negative Sr anomaly, without obvious Ce and Eu anomalies. Such characteristics indicate that the basaltic porphyry magmas originated from partial melting of metasomatic lithospheric mantle peridotite, and the basaltic magma erupted after oxidation and fractional crystallization. It is therefore proposed that the termination of the North China Craton Mesozoic lithosphere thinning can be restricted to ca. 105 Ma in the Early Cretaceous, and the Xingcheng basaltic magma shows ancient island arc magma affinity. The slab rollback of the subducted Paleo-Pacific plate with high-angle was the dominant geodynamic mechanism, and the overlying lithospheric mantle was heated, corroded, and delaminated, which seems to have been the secondary mechanism.

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何登洋,邱昆峰,张莲,于皓丞,杨泽宇,2020,华北克拉通兴城早白垩世玄武玢岩锆石、金红石地球化学特征及其地质意义[J].岩石矿物学杂志,39(6):735~750.

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  • 收稿日期:2020-04-29
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  • 在线发布日期: 2020-11-13
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