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锆石SHRIMP U-Pb定年结果显示:内蒙古中部白音乌拉地区原宝力高庙组的流纹岩形成时代为300.0±2.9 Ma,属晚石炭世;青格勒宝拉格地区原宝力高庙组的凝灰岩结晶年龄为159.6±1.4 Ma,并获得3颗捕获锆石的年龄分别为291.8±3.4,304.0±3.3和734.7±9.2 Ma,应属于晚侏罗世满克头鄂博组。锆石LA-MCICP-MS Hf同位素分析显示:流纹岩锆石εHf(t)值为+10.5~+12.9,TDMC值为493~645 Ma;凝灰岩岩浆锆石εHf(t)值为+10.1~+13.1,TDMC值为369~563 Ma。研究结果表明,流纹岩源于晚古生代新生地壳的重熔并混入少量老地壳物质,凝灰岩源于晚古生代地壳的熔融。Hf同位素特征显示晚古生代流纹岩和中生代凝灰岩源于相似的源区,揭示了晚古生代的一次重要的增生事件,并且在约160 Ma时期发生过地壳的再造。结合前人的研究成果表明,兴蒙造山带在约300 Ma时处于古亚洲洋演化过程中岛弧向碰撞后伸展环境的转换时期,在约160 Ma受到蒙古鄂霍茨克构造域的影响。
The zircon SHRIMP U-Pb dating results show that the rhyolite of the former Baolgaomiao Formation in the Baiyinwula area in central Inner Mongolia is 300.0 ± 2.9 Ma, belonging to the Late Carboniferous. The original Baoligao The tuffaceous crystallization age of the Miao Formation is 159.6 ± 1.4 Ma and the age of the three captured zircons is 291.8 ± 3.4, 304.0 ± 3.3 and 734.7 ± 9.2 Ma, respectively, which belongs to the Late Jurassic Mancrübo Obo Formation. The isotopic analysis of zircon LA-MCICP-MS shows that the εHf (t) values of rhyolite are + 10.5 ~ + 12.9 and the TDMC values are 493 ~ 645 Ma; the values of εHf (t) + 13.1, TDMC 369 ~ 563 Ma. The results show that rhyolites originated from the refolding of the Late Paleozoic new crust and mixed with a small amount of the old crustal material, which originated from the melting of the Late Palaeozoic crust. Hf isotopic characteristics show that Late Paleozoic rhyolite and Mesozoic tuff originated from similar source areas, revealing an important Paleozoic accretion event and crustal reformation at about 160 Ma. Combined with the previous research results, it is shown that the Xingmeng orogen at the age of about 300 Ma was in the transitional period from the island arc to the post-collision extensional environment during the evolution of the Paleo-Asian Ocean and was influenced by the Okhotsk tectonism of Mongolia at about 160 Ma.