The earliest Neoproterozoic Nb-enriched mafic magmatism indicates subduction tectonics in the southwestern Yangtze Block, South China

作者：Chen, Fenglin; Cui, Xiaozhuang^*; Lin, Shoufa; Wang, Jian; Ren, Guangming; Li, Kuizhou; Huang, Mingda; Sun, Zhiming; Liu, Shilei; Wang, Peng; Pang, Weihua

来源：Precambrian Research, 2023, 384: 106938.

DOI：10.1016/j.precamres.2022.106938

• Early Neoproterozoic
• Nb-enriched mafic magmatism
• Subduction tectonics
• Yangtze Block
• Rodinia supercontinent

To better reveal the early Neoproterozoic tectonic process of South China with respect to the assembly of the Rodinia supercontinent, an integrated dataset of geochronology, whole-rock geochemistry, and Sr-Nd-Hf isotopic compositions for diabases that intruded the Kunyang Group in the southwestern Yangtze Block is herein presented. Zircon U-Pb dating gives four weighted mean Pb-206/U-238 ages of 946 +/- 4 Ma, 948 +/- 6 Ma, 939 +/- 4 Ma, and 918 +/- 7 Ma, suggesting mafic magmatism in the earliest Neoproterozoic. The diabases possess Nb = 12.3-30.5 ppm, Nb/U = 19.99-37.06, Nb/La = 0.78-1.05, (Nb/Th)(PM) = 0.44-0.80, and (Nb/La)(PM) = 0.75-1.02, geochemically resembling those of typical Nb-enriched basalts. They are tholeiitic in composition with low SiO2 (49.49-51.95 wt%), high TiO2 (2.03-4.65 wt%), MgO (2.50-6.14 wt%), and Fe2O3T (15.38-18.84 wt%) contents. They are enriched in light rare earth elements (LREEs) with weak negative Eu anomalies (Eu/Eu* = 0.75-0.96) and show E-MORB-like characteristics with slight to moderate Nb-Ta depletion. The samples show zircon epsilon(Hf)(t) values ranging from + 5.8 to + 10.3 and whole-rock epsilon(Nd)(t) values from + 0.5 to + 0.9. These elemental and isotopic characteristics suggest that the 0.95-0.92 Ga diabases may have derived from an E-MORB-like magma source with the injection of metasomatized slab melts. Integrating previous studies with our results, we propose that the southwestern Yangtze Block evolved from an intracontinental rift to a passive continental margin in the late Mesoproterozoic, followed by the development of an earliest Neoproterozoic continental arc-back-arc basin system analogous to the Northern Okinawa Trough. The distinct tectonic processes between the southern and northern parts of the Yangtze Block at ca. 1.0-0.9 Ga favour the hypothesis that the final cratonization of the present-day Yangtze Block occurred slightly later than similar to 0.9 Ga in response to the Rodinia supercontinent assembly.

• 单位
  西南石油大学