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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P588.14+6;P595

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    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. HE Deng-yang, QIU Kun-feng, ZHANG Lian, YU Hao-cheng, YANG Ze-yu,2020,Zircon and rutile geochemistry of the Early Cretaceous basaltic porphyry from Xingcheng in the North China Craton and its geodynamic implications[J]. Acta Petrologica et Mineralogica,39(6):735~750.

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History
  • Received:April 29,2020
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  • Online: November 13,2020
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