1�� School of Earth and Space Sciences��Peking University��Beijing 100871��China; 2�� College of Earth Sciences��Jilin University��Changchun 130061��China; 3�� Institute of Geology�� Chinese Academy of Geological Sciences�� Beijing 100037��China

Zircon LA- ICP- MS U- Pb age��geochemical and Nd isotopic data are presented for a newly recognized high- Mg dioritic dike from Haicheng��Liaodong Peninsula��NE China��to constrain its petrogenesis�� The zircons from the high- Mg diorite exhibit striped absorption and oscillatory growth zoning in the cathodoluminescence (CL) images��and have high Th/U ratios (0. 05- - 0. 9)��indicating a magma origin�� Zircon LA- ICP- MS U- Pb dating indicates that 206 Pb/ 238 U ages of 12 spots of zircons are between 167 Ma and 178 Ma��yielding a weighted mean 206 Pb/ 238 U age of 172 ±2 Ma (MSWD =4. 1)��which represents the forming age of the high- Mg dioritic dike��i. e. Middle Jurassic�� Geochemically��the samples have SiO 2 = 55. 4- -60. 6 wt. %��Na 2 O = 2. 2- -2. 76 wt. %��K 2 O =1. 32- - 2. 02 wt. % and (Na 2 O + K 2 O) =3. 82- - 4. 47 wt. %��belonging to sub- alkaline series and displaying a calc- alkaline evolutionary trend�� They are characterized by high MgO(4. 75- - 6. 85 wt. %)��Mg# (55- - 61)��Cr(130- - 262 ppm)��Ni(63- - 130 ppm)��Sr(568- - 857 ppm)��and Ba(484- - 1 130 ppm) contents�� with geochemical features analogous to those of high- Mg adakites�� They show variable ε Nd (t) values ( ��1. 3 to ��3. 9)��with a weighted value of ��2. 7��which plot intermediately between the field of the ancient continental crust and the depleted mantle source��indicating that both the lower crust and mantle source are necessary for the generation of the parent magma of the Haicheng high- Mg diorites�� The Haicheng high- Mg dioritic dike in the Liaodong Peninsula and the Jurassic magmatism in the eastern North China Craton formed under a continental crustal thickening setting that may be related to subduction of the Paleo- Pacific oceanic plate��