Earth Science Frontiers ›› 2018, Vol. 25 ›› Issue (5): 51-68.DOI: 10.13745/j.esf.sf.2018.4.14

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Geochemical characteristics and petrogenesis of Devonian magmatic rocks in the Kalatag district, eastern Tianshan, NW China.

CHEN Lei，WANG Jingbin，DENG Xiaohua，WU Xiangbin，ZOU Haiyang，SUN Yan，XU Jun，ZHANG Wendong   

  1. 1. School of Geosciences and Info-Physics, Central South University, Changsha 410083, China
    2. Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring(Central South University), Ministry of Education, Changsha 410083, China
    3. Beijing Institute of Geology for Mineral Resources, Beijing 100012, China
    4. School of Earth Sciences and Resources, China University of Geosciences(Beijing), Beijing 100083, China
    5. Chengdu Geological Research Institute, Sichuan Metallurgical and Geological Exploration Bureau, Chengdu 610203, China
  • Received:2018-02-08 Revised:2018-06-12 Online:2018-09-15 Published:2018-09-15

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Abstract: We conducted  petrologic investigation and performed major and trace elemental and Sr-Nd isotopic analysis on magmatic rocks from the Kalatag district, eastern Tianshan in order to understand the petrogenesis and geodynamic setting of Devonian magmatic rocks. The results show that Devonian magmatic rocks were mainly composed of intermediate-basic rocks including gabbro, diorite, quartz diorite, monzonite and andesite. Gabbro was calc-alkaline to tholeiitic with high Al2O3 content (18.96%19.06%) and Mg# value (57.2869.37), yielding A/CNK value of 0.730.88. Diorite, quartz diorite, monzonite and andesite were calc-alkaline to high-K calc-alkaline with high Al2O3 contents (15.02%17.43%) and Mg# values (53.6772.91), and A/CNK values of 0.731.17. Sr-Nd isotopic analysis yielded positive εNd(t) values ranging from 5.36 to 7.72 with low initial 87Sr/86Sr ratios of 0.70311 to 0.70518. Devonian magmatic rocks were enriched in large ion lithophile elements (Rb, Ba and K) while depleted in high field strength elements (Ta, Nb and Ti). These geochemical characteristics indicate that Devonian magmatic rocks were derived from the same magma chamber with an enriched mantle wedge metasomatized by subduction slab fluid and emplaced in an island arc setting during the northward subduction of the Kanggur Ocean.

Key words:  geochemistry, petrogenesis, Devonian, Kalatag district, eastern Tianshan

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