北山造山带东段芨芨泉岩体地球化学特征、锆石U-Pb年代学及其构造意义

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

北山造山带东段芨芨泉岩体岩性为辉长岩和辉绿岩,LA-ICP-MS锆石U-Pb测年获得(274.1±5.3)Ma的锆石结晶年龄,表明该岩体形成于早二叠世。岩体地球化学数据显示:岩石具有较低SiO_2、较高的Al_2O_3和CaO及较高的Mg~#,稀土元素总量较低,轻重稀土分异不明显,弱正Eu异常,岩石富集大离子亲石元素(Rb、Ba、K),亏损高场强元素(Nb、Ta、P、Zr)。岩石地球化学特征表明,岩浆起源于亏损地幔的部分熔融、上升过程中受到地壳物质的混染,结合区域地质背景,认为芨芨泉岩体形成于板内伸展构造背景。

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 SiO_2 content,relatively high Al_2O_3 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.