鲁东昆嵛山地区宫家辉长闪长岩成因: 岩石地球化学、锆石U-Pb年代学与Hf同位素制约

Gongjia gabbro-diorite pluton is the biggest outcropped basic intrusion in the Kunyushan area, Jiaodong Peninsula. Zircon LA-ICP-MS U-Pb dating gives that its emplacement age of 113 ± 2Ma. Their low SiO₂ and high MgO content (Mg^# up to 56) indicate that the gabbro-diorite was originated from a mantle source. The rocks are enriched in LREEs and LILEs, such as K, Rb, Ba, Th and U, and depleted in HFSEs, such as Nb, Ti and P. They have initial Sr isotopic ratios (I_Sr) of 0.70745 - 0.70812 and ε_Nd values varying from - 15.9 to - 12.0. Sr and Nd isotope, together with Pb isotope [(²⁰⁶Pb/²⁰⁴Pb)_i = 17.108 - 17.239], of the gabbro-diorite are similar to those of mafic dykes and Cretaceous Qingshan group volcanic rocks in the Jiaolai basin. Zircon Hf isotope composition is relatively homogeneous with an average ε _Hf(t) value of - 16.7, indicating that their parental magmas were derived from an enriched lithospheric mantle beneath the North China, coupled with fractional crystallization. The Gongjia gabbro and diorite pluton was result of lithospheric thinning in the Jiaodong Peninsula and even eastern North China craton in the early Cretaceous.