GEOCHRONOLOGY AND GEOCHEMISTRY OF THE LAMPROPHYRE DIKES IN QIXIA AREA, SHANDONG PROVINCE: Geological Implication

The paper studies the petrography, zircon U-Pb chronology and petrogeochemistry of the lamprophyre dikes in Hexikuang area of Qixia, Shandong Province. The zircon U-Pb dating results show that the age of zircons in the lamprophyre can be divided into four age intervals: 151-163 Ma, 212-230 Ma, 1 822-1 962 Ma and 2 431-(2 613±37) Ma. The ²⁰⁶Pb/²³⁸U ages of eight young zircons range from (151±2) to (163±4) Ma, with the weighted mean age of 153.7±2.8 Ma, which represents its formation age. The others are inherited zircons, indicating that they are contaminated by crust-derived materials during magmatic activity. The lithogeochemical analysis results reveal that the lamprophyre in the area is characterized by enrichment of Rb, Ba, Th, Pb and LREEs, and relative depletion of Ta, Nb, Zr, Hf and Ti. From the above, it is concluded that the lamprophyre was formed in the volcanic arc environment under the background of subduction of Pacific Plate beneath Eurasian Plate, and was contaminated by crust-derived materials during its ascent.