SONG Yuhang, XIE Chaoming, YU Yunpeng, ZHU Lidong, HAO Yujie, YANG Chen. Age, petrogenesis and tectonic setting of bimodal volcanic rocks from Yeba Formation in Maizhoukunggar, southern Tibet[J]. Geological Bulletin of China, 2022, 41(8): 1369-1381. DOI: 10.12097/j.issn.1671-2552.2022.08.005
    Citation: SONG Yuhang, XIE Chaoming, YU Yunpeng, ZHU Lidong, HAO Yujie, YANG Chen. Age, petrogenesis and tectonic setting of bimodal volcanic rocks from Yeba Formation in Maizhoukunggar, southern Tibet[J]. Geological Bulletin of China, 2022, 41(8): 1369-1381. DOI: 10.12097/j.issn.1671-2552.2022.08.005

    Age, petrogenesis and tectonic setting of bimodal volcanic rocks from Yeba Formation in Maizhoukunggar, southern Tibet

    • The study of the Early Mesozoic magmatic rocks in the southern Tibetan Plateau is of great significance to the inversion of regional tectonic evolution.The volcanic rocks of the Yeba Formation in Early Jurassic are considered to be the early records of the subduction of the Neo-Tethys ocean.At present, there are still controversies about the tectonic setting of their formation.We selected the volcanic rocks of Yeba Formation in Maizhoukunggar county, southern Tibet, as the research objects.We present new zircon U-Pb isotopes and whole rock geochemical composition testing, discuss the implications for evolution of this region.The main lithology includes basalts(181.0±5.0 Ma, n=1)and rhyolites(181.4±4.4 Ma, MSWD=0.017, n=18), and they have bimodal volcanic characteristics.The basalts have high TiO2(1.62%~1.78%), P2O5(0.49%~0.51%)and Nb(10.18%~10.61%)concentrations, (La/Nb)PM < 2, which are similar to the ENB.The Mg#s are between 54.9~57.3, enrichment of LREE and depletion of HREE.Rhyolites have highly SiO2 (79.25%~80.22%), Na2O(3.94%~4.26%)contents, Mg # values are 49.1~50.4, Th/Ce ratios are 0.1~0.15, Th/La ratios are 0.22~0.31, Nb/Ta ratios are 14.06~14.32, Sr /Y ratios are 4.15~4.82, and enrichment of LREE and LILE and depletion of HFSE.It is considered that the magma source area of basalts is mantle wedge metasomatized by slab-derived melt and mixed with crustal materials during the later evolution.Rhyolites are of mantle derived magma mixed with continental crust.Basalts have the characteristics of intraplate basalts and island arc magmatic rocks, while rhyolites show the characteristics of island arc magmatic rocks. Combined with the regional geological background, it is inferred that the volcanic rocks of the Yeba Formation in Maizhoukunggar were formed in the back-arc basin of the northward subduction of the Neo-Tethys ocean, and there are differences in the formation age and tectonic settings of the volcanic rocks of the Yeba Formation in the region, It may represent different products in different stages of subduction.
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