U-Pb isotopic dating of basalt from the Gajinxueshan Group in the Jinshajiang tectonic belt
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摘要: 以U Pb单颗粒锆石同位素稀释法 ,测定了嘎金雪山岩群中两件玄武岩样品的同位素年龄。获得的两个下交点年龄分别为 (36 2± 8)Ma和 (396± 7)Ma ,两个上交点年龄分别为 (2 52 5± 12 )Ma和 (1387± 59)Ma。前者代表嘎金雪山岩群玄武岩的生成年龄 ,说明金沙江洋在早石炭世就已打开 ;后者代表下伏基底年龄 ,表明金沙江构造带深部可能存在具扬子古陆壳性质的中—早元古宙地层 ,从而表明金沙江洋是由扬子古陆边缘裂解而成的。Abstract: Two basalt samples from the Gajinxueshan Group were dated by using single zircon U Pb isotope dilution method. The two lower intercept points yield age of 362±8 Ma and 296±7 Ma respectively, whereas the two upper intercepts yield 2 525±12 Ma and 1387±59 Ma respectively. The former are interpreted to date the formation age of the basalt, suggesting that the Jinshajiang ocean opened in the early Carboniferous. The latter represent the age of the underlying basement, implying a Proterozoic Yangtze type continental crust at depth. All these indicate that the Jinshajiang ocean was formed by rifting on the margin of the Yangtze continent.
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Keywords:
- Jinshajiang tectonic belt /
- Gajinxueshan Group /
- basalt /
- U Pb isotopic dating
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