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| GEOCHRONOLOGY, GEOCHEMISTRY AND ORIGIN OF THE EARLY CRETACEOUS JIANYI PLUTON IN DASHIQIAO, LIAONING PROVINCE |
| LI Zhuang1, MENG En2, PEI Fu-ping3, LIU Jing-wei1, ZHANG Lu1 |
1. School of Earth and Space Sciences, Peking University, Beijing 100871, China;
2. Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;
3. College of Earth Sciences, Jilin University, Changchun 130061, China |
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Abstract The Jianyi pluton, located in Dashiqiao, Liaoning Province, Northeast China, is dominated by granodiorite. The zircons from the granodiorite show euhedral shape, oscillatory and sector-zoning, with high Th/U ratios (> 0.1), suggesting a typical magmatic origin. LA-ICP-MS zircon U-Pb dating indicates that the 206Pb/238U ages of zircons range from 138 to 145 Ma, yielding a weighted mean age of 140 Ma, which probably represents the formation age of the granodiorite, i.e., Early Cretaceous. Major element characteristics show that the Jianyi pluton belongs to metaluminous I-type granite. The chondrite-normalized REE patterns suggest enrichment of LREEs, and depletion of MREEs and HREEs, with slightly negative Eu anomaly, indicating a strong fractional crystallization of amphibole and weak fractional crystallization of plagioclase. The trace element spider diagram shows that they are enriched in large ion lithophile elements(LILEs, such as Rb, Th and U) and depleted in high field strength elements(HFSEs, Nb and Ta). The Nb/Ta, La/Nb and Th/Nb values are between the data of the crust and mantle, showing that the magma is derived from crust-mantle mixed source. Integration of our new data with recent geological studies concludes that the Jianyi pluton and the Early Cretaceous magmatism in the eastern North China craton was formed in an extensional setting similar to back-arc basin, which may be related to the subduction of the Paleo-Pacific oceanic plate.
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Received: 31 July 2015
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2016, Vol. 25 
