Zircon U-Pb age,geochemical and Nd isotopic data of Middle Jurassic high-Mg dioritic dike in Liaodong Peninsula,NE China |
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| Authors: | LI Zhuang ;PEI Fuping ;MENG En |
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| Institution: | 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 |
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| Abstract: | 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． |
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| Keywords: | Liaodong Peninsula high-Mg diorite zircon U-Pb age geochemical Nd isotope |
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