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横现河地区张岩沟双峰式火山岩位于勉略构造带三岔子—略阳段,由紧密共生的变质基性火山岩和变质中酸性火山岩组成,其原岩为亚碱性玄武岩和亚碱性流纹-英安岩。中酸性火山岩稀土元素含量明显低于玄武岩,表明中酸性火山岩为地壳部分熔融形成,而非分离结晶成因。玄武岩具有较高的Zr含量与较高的Zr/Y值,表现出板内玄武岩特征,其具有的弧印记应为陆壳物质混染所致。LA-ICP-MS锆石U-Pb测试结果表明,流纹岩成岩年龄为(728±10)Ma(n=4,MSWD=0.14)。结合区域地质背景,认为张岩沟双峰式火山岩形成于地壳伸展机制下的大陆裂谷环境,预示着该地区新元古代洋盆的打开。这一新成果,对研究勉略带新元古代的构造演化以及探讨扬子地块北缘对Rodinia超大陆裂解的响应具有重要意义。
The Hengyanhe bimodal volcanic rock of Zhangyougou is located in the Sanchazi-Lueyang segment of the Mianlue tectonic zone and is composed of closely interbedded metamorphic basement volcanic rocks and metamorphic intermediate-acidic volcanic rocks. The original rocks are subbasin basalt and sub-alkaline Lime pattern - English rock. The REE content of the intermediate-acidic volcanic rocks is significantly lower than that of the basalts, indicating that the intermediate-acidic volcanic rocks are partly formed by melting of the crust, rather than from the separate crystallization. Basalt has high Zr content and high Zr / Y value, showing intraplate basalt characteristics, which have arc marks due to contamination by continental crust material. LA-ICP-MS zircon U-Pb results show that the diagenetic age of rhyolite is (728 ± 10) Ma (n = 4, MSWD = 0.14). Combined with the regional geological background, it is concluded that the bimodal volcanic rocks in Zhangyougou are formed in the continental rift environment under the crustal extension mechanism, which indicates the opening of the Neoproterozoic oceanic basins in the area. This new achievement is of great significance to the study of the Neoproterozoic tectonic evolution and the response of the northern margin of the Yangtze block to the Rodinia supercontinent cracking.