华北克拉通西南缘高山河组凝灰岩锆石U-Pb年龄及其地质意义

Zircon U-Pb dating of the Gaoshanhe Formation tuff in the southwesternmargin of the North China craton, and its geological singificance

华北克拉通西南缘高山河组是中元古代重要的地层单元之一,但其沉积时限和地层对比关系长期存在争论。本文对采自甘肃省华亭县马峡镇高山河组下部的凝灰岩进行了LA-ICP-MS锆石U-Pb同位素年龄测定,获得凝灰岩样品的高精度年龄为1759±17Ma。结合区域资料和前人研究成果,初步将该地区高山河组的形成年代限定在1770～1600Ma之间,并进一步限定高山河组下部熊耳群火山岩系的形成时代介于1800～1770Ma之间。此为首次在华北克拉通西南缘高山河组获得高精度年龄,不仅确定了高山河组沉积时代应为长城纪,也为整个华北克拉通西南缘中元古代地层划分对比和地质演化及其进一步进行微古生物研究等地质问题奠定了重要的年代学基础。

The Gaoshanhe Formation developed in the southwestern margin of the North China Craton(NCC) is one of the most important Mesoproterozoic stratigraphic units. However, its depositional age and regional correlation have been debated for a long time. In this study, the LA-ICP-MS zircon U-Pb dating results show that the tuff samples from the lower Gaoshanhe Formation of the Maxia section in Huating, Gansu produces U-Pb ages of 1759±17 Ma. Combined with the regional data and previous study results, the depositional internal for the Gaoshanhe Formation can be limited roughly in to the period from 1770~1600 Ma, and further prove that the Xiong’er Group were erupted mainly from 1800~1770 Ma. With this data, the depositional age of the Ganshanhe Formation in the southwestern margin of the NCC can be calibrated accurately as the first time. It not only confirms the stratigraphic age, but also has great significance for the division and correlation of the Mesoproterozoic strata in the whole southwestern margin of the NCC and furtherly studying the micropalaeontology in the southwestern margin of the NCC.