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Geoscience ›› 2025, Vol. 39 ›› Issue (03): 588-597.DOI: 10.19657/j.geoscience.1000-8527.2025.039

• Machine Learning and Its Applications in Mineralogy • Previous Articles     Next Articles

Geochemical Characteristics and Petrogenesis of Carboniferous Volcanic Rocks in the Northwestern Margin of the Junggar Basin

NIU Huapeng1,2(), LIU Shan1,2, JIAO Xiaoqin3, ZHANG Guanlong4, WANG Qianjun4, ZHOU Jian4, ZHAO Xian1,2, YU Hongzhou4, XIONG Zhengrong4, HE Xiao1,2   

  1. 1. State Key Laboratory of Petroleum Resources and Engineering, China University of Petroleum (Beijing), Beijing 102249, China
    2. College of Geosciences, China University of Petroleum (Beijing), Beijing 102249, China
    3. Department of Geosciences, University of Padova, Padua, Italy
    4. Research Institute of Exploration and Development, Sinopec Shengli Oilfield Company, Dongying, Shandong 257015, China
  • Online:2025-06-10 Published:2025-07-03

Abstract:

This study investigates Carboniferous volcanic rocks (basalt, basaltic andesite, and andesite) from the Hara Arat Mountain (Hashan) area on the northwestern margin of the Junggar Basin to elucidate their petrogenesis and tectonic setting. Results indicate that these three rock types exhibit moderate MgO content (3.21%-6.82%), moderate to high Al2O3 content (11.30%-17.78%), and elevated total alkali content (K2O+Na2O=4.24%-7.24%). Basalt samples show relatively low K2O content, reflecting Na-enrichment relative to K, and are classified as low-K tholeiitic basalts. In contrast, basaltic andesites and andesites display high calc-alkaline element contents, consistent with island arc volcanic rock characteristics. Isotopic analyses reveal medium-low 87Sr/86Sr ratios (0.702877-0.706620) and high εNd(t) values (+4.59 to+9.85), indicating magma interaction between crustal and mantle components in a deep magma chamber. Compared to basalts, basaltic andesites and andesites show enrichment in large ion lithophile elements (e.g., Ba), relative enrichment in high field strength elements (e.g., U, Pb), and depletion in Nb, typical of subduction-related island arc magmatism. Trace element and rare earth element patterns suggest that basalts originated from depleted mantle melts under a convergent tectonic regime, while intermediate volcanic rocks record the subduction of oceanic plates beneath continental plates. This process involved the replacement of the depleted mantle wedge by sediments or melts derived from the dehydrating subducting slab, followed by partial melting to form basaltic andesites and andesites. Combined with regional geological data, the subduction of the oceanic plate persisted until the late Carboniferous.

Key words: Junggar Basin, Hashan, Carboniferous, volcanic rock, petrogenesis

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