Zircon U-Pb age,geochemical and Nd isotopic data of Middle Jurassic high-Mg dioritic dike in Liaodong Peninsula,NE 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 that206 Pb /238 U ages of 12 spots of zircons are between 167 Ma and 178 Ma,yielding a weighted mean206 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 SiO2= 55. 4--60. 6 wt. %,Na2 O = 2. 2--2. 76 wt. %,K2 O = 1. 32--2. 02 wt. % and( Na2 O + K2O) = 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 εNd( 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.