U-Zircon U-Pb Dating and Geochemistry of Jijiquan Pluton in the Eastern Section of Beishan Orogenic Belt and their Tectonic Implications

The Jijiquan plution in the eastern section of Beishan Orogenic Belt consists of gabbro and diabase. The zircon LA-ICP-MS dating has obtained an age of (274.1±5.3) Ma, which reveals that this pluton was formed in Early Permian. The geochemical data shows that these rocks have low SiO₂ content, relatively high Al₂O₃ and CaO content as well as Mg^# value, low total REE contents, no obvious fraction of LREE and HREE, weak positive Eu anomly, enrichment of LILE and depletion of HFSE. The geochemical features indicate that the magma was formed by the partial melting of depleted mantle, which was suffered the crust contamination in the magma rising process. After analyzing the regional geological background, it is considered that the Jijiquan pluton was formed at an intraplate extensional tectonic setting.