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Geochronological, geochemical, and geological significance of Jianshan and Shibanjing granites in the Gongpoquan Arc, Beishan Orogenic Belt

WANG Xin-yu;YUAN Chao;LONG Xiao-ping;ZHANG Yun-ying;LIN Zheng-fan;State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences;University of Chinese Academy of Sciences;Department of Geology, Northwest University;  
Jianshan and Shibanjing granitic plutons developed in in the middle of the Gongpoquan arc, Beishan orogenic collage. Jianshan granodiorites show characteristics similar to classical adakites, e.g., high Si O2( 56%), Al2 O3( 15%), Sr( 400 μg/g) contents and Na2 O(Na2 O K2 O) values, high Sr/Y(60~88),(La/Yb)N(7.73~15.5) ratios, but low Y(8.15~11.2 μg/g) and Yb(0.57~1.01 μg/g) values with weak positive Eu anomalies(δEu = 1.04~1.27), while Shibanjing granites do not show adakitic characteristics. LA-ICPMS zircon U-Pb ages of Jianshan pluton and Shibanjing pluton are(363.4±2.9) Ma and(362.6±3.0) Ma, respectively. Both the two plutons are enriched in large ion lithophile elements(LILEs), depleted in high field strength elements(HFSEs, e.g., Nb, Ta), and have evolved Sr-Nd isotopes(Jianshan:(87 Sr/86 Sr)0(0.7057–0.7058) and εNd(from-0.4 to-1.1); Shibanjing:(~(87)Sr/~(86)Sr)0(0.7070–0.7071) and εNd(t)(-2.9 –-2.6)), indicating some crustal contamination. By synthesizing regional data, we suggest that the formation of Jianshan and Shibanjing plutons are related to the southward subduction of the Xiaohuangshan Ocean. Furthermore, the Late Devonian adakites have high ore potential.
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