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Geoscience ›› 2020, Vol. 34 ›› Issue (03): 399-417.DOI: 10.19657/j.geoscience.1000-8527.2020.011

• Petrology •     Next Articles

Zircon U-Pb Geochronology, Geochemistry Characteristics and Geological Significance of the Solonker Ophiolite, Inner Mongolia

LIU Zhihua1,2(), GU Xuexiang1,3(), ZHANG Yongmei1,2,3, WANG Jialin3, LIU Tao4, WANG Wendong4, ZHAO Wei1, CHEN Yang1   

  1. 1. School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China
    2. State Key Laboratory for Mineral Deposits Research, Nanjing University, Nanjing, Jiangsu 210046, China
    3. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China
    4. Harbin Natural Resources Comprehensive Investigation Center, China Geological Survey, Harbin, Heilongjiang 150081, China
  • Received:2019-06-04 Revised:2019-12-10 Online:2020-07-04 Published:2020-07-05
  • Contact: GU Xuexiang

Abstract:

To deepen our understanding on the Late Paleozoic tectonics of the eastern Central Asian Orogenic Belt, a study of the petrology, geochronology and geochemistry of fresh basalts and gabbros in the Solonker ophiolitic mélange belt were reported. Zircon grains from these basalts and gabbros yielded206Pb/238U ages of (276.7±2.7) Ma and (274.1±3.2) Ma, respectively, indicating an Early Permian emplacement age. Both the basalts and gabbros are tholeiitic, and have low Mg# values of 41-50 and 62-65, respectively, both below the primary magma value. Meanwhile, the basalt and gabbro samples fall along a fractionation trend in the Harker diagrams, suggesting a dominant role of fractional crystallization in the magma evolution.The Th/La, Th/Ce and Lu/Yb ratios of the two rock types are below those of the average continental crust, but similar to those of typical mantle-derived magmas. Therefore,it is inferred that crustal contamination had little influence on the mafic magmas.Rare earth element (REE) compositions show that the basalts are of the N-MORB-type with light REE (LREE) depletions,probably originated from 5%-10% partial melting of the depleted spinel lherzolite mantle. Gabbros are slightly LREE-depleted with a flat REE distribution pattern, and have clearly lower total REEs (Σ REEs) than N-MORB, probably due to a higher degree of partial melting than the basalts in the source region.In addition, both rock types are highly enriched in large ion lithophile elements (LILEs: Rb, Sr, Ba, Pb) and depleted in high-field-strength elements (HFSEs: Nb, Ta), similar to typical island arc magmas.These features imply that their magmas were affected by subduction-related fluids, or were derived from the melting of subducting sediments.The geochemical characteristics indicate that the Solonker ophiolites belong to the supra-subduction zone (SSZ)-type, and may have formed in an intra-oceanic backarc basin.This indicates that intra-oceanic subduction still persisted till at least the Early Permian in the study area.Comprehensive analyses suggest that the Paleo-Asian Ocean(PAO) was closed in the Late Permian to Early Triassic along the Solonker-Xar Moron suture zone.

Key words: ophiolite, geochronology, geochemistry, Paleo-Asian Ocean, Solonker, Inner Mongolia

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