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Geoscience ›› 2020, Vol. 34 ›› Issue (03): 418-430.DOI: 10.19657/j.geoscience.1000-8527.2020.017

• Petrology • Previous Articles     Next Articles

Zircon U-Pb Chronology, Geochemistry Characteristics of the Tiezhai Complex in Linqu County of Western Shandong and Their Geological Significance

YU Lidong1(), YU Xuefeng2,3,4(), LI Dapeng2,3,4, LIU Qiang1,2,3,4, LIU Jiajun1, SHU Lei2,3,4, WEI Pengfei1,2,3,4   

  1. 1. School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083,China
    2. Shandong Geological Sciences Institute, Jinan, Shandong 250013, China
    3. Key Laboratory of Gold Mineralization Processes and Resources Utilization Subordiated to the Ministry of Natural and Resources, Jinan, Shandong 250013,China
    4. Shandong Key Laboratory of Geological Processes and Resource Utilization in Metallic Minerals, Jinan, Shandong 250013, China
  • Received:2018-09-05 Revised:2019-12-30 Online:2020-07-04 Published:2020-07-05
  • Contact: YU Xuefeng

Abstract:

The Tiezhai complex is located in Linqu County of western Shandong Province, and is mainly composed of grey and light-red quartz monzonite porphyries. To accurately determine the formation age and geochemical characteristics of the complex, we studied the major and trace elements (including REEs), and zircon LA-ICP-MS ages of the grey and light-red quartz monzonite porphyries. Our zircon U-Pb dating reveals that the grey quartz monzonite porphyry was formed in (129.0±1.7) Ma, and contains many Precambrian inherited zircons with ages of (2,520±30) Ma. The light-red quartz monzonite porphyry was formed in similar age at (125.0±1.6) Ma. The rocks are all rich in Si and alkali, but low in Ca and Mg. The grey quartz monzonite porphyry has a higher Mg# value than its light-red counterpart.Their total REE contents are relatively low, and the LREE/HREE fractionation is high with no Eu anomaly. The rocks have high Sr and Ba contents, and with negative HFSE (high field strength elements,e.g.,Nb, Ta and Ti) anomalies.Geochemical characteristics of the two porphyries indicate that parental magma of the Tiezhai complex may have sourced from partial melting of the enriched mantle and the assimilation of some ancient crustal materials. The difference in Mg# between the two porphyries was likely resulted from magnetite fractionation. Dehydration of the Pacific subducted slab resided in the mantle-crustal transition zone was likely the cause of the Early Cretaceous lithospheric thinning. Voluminous magmatic rocks were generated in this period, indicating that the lithospheric thinning had peaked during the Early Cretaceous in the North China Craton.

Key words: petrogenesis, zircon U-Pb dating, Tiezhai complex, western Shandong

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