南秦岭随枣地块耀岭河组双峰式火山岩:对扬子克拉通北缘大陆裂解过程的约束

Recognition of Late Neoproterozoic bimodal volcanic rocks from the Yaolinghe Formation in the Suizao terrane of South Qinling massif and constraints on the continental rifting of the northern margin of Yangtze craton

长期以来,扬子克拉通北缘新元古代地质构造演化一直是地学界研究的热点。在南秦岭随州地区耀岭河组中新识别出一套双峰式变火山岩,对其开展锆石U-Pb年代学研究结果表明,变玄武岩中锆石较少,且多为捕获锆石,年龄组成特征与下伏武当岩群顶部岩石中碎屑锆石基本一致;白云母千枚岩中锆石年龄集中,获得的U-Pb年龄为623±3 Ma,代表了南秦岭随枣地区耀岭河组的形成时代,该结果与侵入武当岩群中的基性岩墙年龄650~600 Ma一致,两者应为同时期不同产出相的岩浆作用的产物。结合区域研究成果,扬子克拉通北缘裂解可能经历了更长期且复杂的地质构造过程,西部裂解较早,东部(现今方向)较晚,总体呈"拉链式"裂解模式。

Neoproterozoic tectonic evolution of the northern Yangtze craton is of great significance to the Precambrian geological evolution of South China.Zircon samples collected from the newly recognized bimodal meta-volcanic rocks of the Yaolinghe Formation in the Suizhou area were dated by LA-ICP-MS U-Pb method. Most zircons in the matabasalts are inherited zircons, their ages are consistent with those of detrital zircons from the underlying Wudang Formation in the region.Geochronological results also indicate that the muscovite-phyllites( felsic rocks) were formed at 623 ± 3 Ma, representing the sedimentary age of the Yaolinghe Formation,synchronous with the 650-600 Ma intrusive sills in the Suizao terrane.Combined with the new geochronological data recording riftingrelated magmatic-sedimentary rocks during the Late Neoproterozoic in the northern margin of the Yangtze craton,it can be advocated that the breakup of the Rodinia supercontinent in the northern part of the Yangtze craton might have been a long-lasting process. An oblique diachronous rifting model is further hypothesized for the breakup process.