辽东榛子沟铅锌矿煌斑岩锆石U-Pb年代学、地球化学特征及其地质意义

摘要

The petrographical, zircon U-Pb dating, geochemical and Sr-Nd isotopic characteristic of lamprophyres in Zhenzigou Pb-Zn deposit, Qingchengzi, Liaodong peninsula. Zircon LA-ICP-MS U-Pb dating yields an age of (227.70±1.30) Ma, the lamprophyres are the product of late Indosinian magmatism in North China Craton(NCC). Geochemically, the lamprophyres have high values of potassium (K2O/Na2O are 2.34~3.64), alkaline (K2O+Na2O are 4.12~4.67) and are enriched in large ion lithophile elements (Rb, Ba) and LREEs and depleted in the high field strength elements (Nb, Ta, Zr, Hf) and HREEs. The isotopic of lamprophyres are characterized by high (87Sr/86Sr)I (0.71224~0.71248),lowεNd(t) (−1.53~−0.43). Based on the geochemistry and isotope, the lamprophyres were derived from EMⅡ which are metasomatized by the enriched in large ion lithophile elements while depleted in the high field strength elements fluid from the dehydration of the subducted plate, which was not obvious undergo contamination of crust in the process of magma rising. Combined with regional tectonic evolution, the lamprophyre is originated from slab break-off during the process of Yangtze Craton and North China Craton continental deep subduction.%阐述辽东榛子沟铅锌矿区煌斑岩岩相学、锆石U-Pb年代学、元素地球化学及Sr-Nd同位素地球化学特征。锆石LA-ICP-MS U-Pb定年结果表明煌斑岩侵位时代为(227.7±1.3) Ma，属于晚三叠世。岩石地球化学分析表明煌斑岩具有高钾(K2O/Na2O为2.34~3.64)、富碱(K2O+Na2O为4.12~4.67)，富集大离子亲石元素(Rb、Ba)和轻稀土元素，亏损重稀土元素和高场强元素(Nb、Ta、Zr、Hf)特征。同位素显示高(87Sr/86Sr)i(0.71224~0.71248)低εNd(t)(−1.53~−0.43)特点。岩石地球化学和同位素特征表明，煌斑岩可能为 EMⅡ型富集地幔部分熔融的产物，推测源区可能与板块俯冲带组分脱水产生的富集LILE而亏损HFSE的流体交代富集地幔有关，岩浆上升过程中未发生明显的地壳混染作用。结合区域构造演化，认为扬子克拉通向华北克拉通深俯冲过程中板片断离可能是该区煌斑岩形成的地球动力学背景。