胶东范家庄地区晚侏罗世低镁埃达克质花岗岩成因及构造背景

胶东地区广泛发育一系列晚侏罗世岩浆作用产生的埃达克质岩，其成因机制及构造背景研究为揭示胶东地区中生代构造演化提供了重要证据.选取出露于胶东苏鲁地区的范家庄花岗岩进行锆石U-Pb年龄、全岩主微量元素和Sr-Nd-Pb同位素组成分析，探讨了岩石成因及成岩构造背景.锆石U-Pb年龄结果表明范家庄花岗岩侵位于晚侏罗世（161±2 Ma）.岩石主微量数据具有富硅（SiO₂=68.94%~71.00%）、高铝（Al₂O₃>15.17%）、低镁（MgO=0.32%~0.41%）；高Sr、低Y、Yb含量以及高（La/Yb）_N（>38.59）比值的特点，同位素测试结果显示相对高的（87Sr/86Sr）_i比值（0.709 28~0.711 41）、相对较低的ε_Nd（t）值（-20.5~-14.1）和高放射性Pb同位素组成（206Pb/204Pb）_t=16.853~17.207，（207Pb/204Pb）_t=15.436~15.495，（208Pb/204Pb）_t=37.340~37.629.综合分析认为，范家庄岩体属于低镁埃达克质岩，产于增厚下地壳部分熔融，源区以扬子板块下地壳组分为主，混合有华北板块下地壳成分.晚侏罗世伊泽奈奇板块俯冲形成的弧后拉张环境诱发重力不稳定或者岩石圈伸展造成加厚的造山带垮塌，软流圈上涌的导致加厚地壳部分熔融可能是形成胶东范家庄低镁埃达克岩的地球动力学背景. 

Petrogenesis and Tectonic Setting of the Late Jurassic Low-Mg Adakitic Granites in the Fanjiazhuang Area,Jiaodong Peninsula

A series of late Jurassic adakitic rocks are widely developed in the Jiaodong Peninsula, eastern China, and their petrogenesis and tectonic setting provide important evidence for Mesozoic tectonic evolution in Jiaodong area. In this study, we investigate the bulk-rock major element, trace element and Sr-Nd-Pb isotopes of the granitoid exposed in the Fanjiazhuang area. LA-ICP-MS zircon U-Pb dating results yield a weighted mean 206Pb/238U age of 161±2 Ma for the Fanjiazhuang granitoid. Geochemical data indicate that the intrusion is characterized by high SiO₂(68.94%-71.00%), Al₂O₃(>15.17%), Sr but low MgO(0.32%-0.41%), Y and Yb contents, and high Sr/Y and La/Yb ratios. The rocks exhibit high initial 87Sr/86Sr ratios (0.709 28 to 0.711 41), low ε_Nd(t) (-20.5 to -14.1) and they are characterized by high radiogenic Pb isotopic compositions with (206Pb/204Pb)_t=16.853-17.207, (207Pb/204Pb)_t=15.436-15.495, (208Pb/204Pb)_t=37.340-37.629. The elemental and isotopic data suggest that the late Jurassic low-Mg adakitic granites in Fanjiazhuang area were derived from the partial melting of the thickened lower crust. The results show that the magma sources were dominated by lower crust of the Yangtze Block and with subordinate lower crust of the North China Block. The Izanagi plate subduction was the most likely geodynamic force for formation of the Jurassic Fanjiazhuang low-Mg adakatic granite in the Jiaodong Peninsula.