秦岭造山带主要疑难地层时代研究的新进展

New Advances in the Study on Ages of Metamorphic Strata in the Qinling Orogenic Belt

通过区域与剖面地质调查,结合古生物学、同位素年代学和构造地质学等方法研究,在秦岭主要疑难地层中发现了众多化石,并获得一批同位素年代数据,重新厘定了地层时代。在变质哑地层:1)宽坪群中发现了奥陶纪化石;2)耀岭河群和郧西群中发现石炭纪化石,并测得相应同位素年龄;3)三花石群中发现泥盆纪化石。在有争议地层碧口群中发现泥盆纪化石,厘定其主体时代为泥盆纪;在原划寒武?奥陶系洞河群中发现晚古生代化石,更正了北大巴山腹地没有上古生界的普遍认识;将南秦岭原志留系及相伴的下古生界厘定为于二叠纪末或三叠纪最终形成的增生杂岩带,否定其为被动陆缘沉积地层。

Many micro-fossils and chronologic data were obtained in the metamorphic strata of the Qinling Orogenic Belt through palaeontologic, chronologic and structural studies in recent geological survey. Ordovician fossils were found in the Kuanping and Taowan Groups in North Qinling; Carboniferous fossils were found in the Yaolinghe and Yunxi Groups （formerly assigned to Late Proterizoic） and their isotopic ages were determined; Devonian fossils were also found in the Sanhuashi and Bikou Groups （formerly assigned to Late Proterozoic） and Donghe Group （formerly assigned to Early Paleozoic） in South Qinling. An accretionary complex belt was determined, and it is composed of Silurian strata and its Lower Paleozoic concomitant strata north of the Mianxian-Lueyang-Yangxian-Shiquan-Ankang fault in South Qinling. The final formation age of this belt was deduced to be Late Permian or Early Triassic by new findings of fossils and dating of debris zircon in matrices made up of turbidites.