滇中北部昆阳群凝灰岩SHRIMP锆石U-Pb年龄及其地层学意义

SHRIMP zircon U-Pb age of the Kunyang Group in northern Central Yunnan Province and its stratigraphic significance

滇中昆阳群一直是华南前寒武纪地质研究的热点之一,其地层序列、时代与区域对比长期存在争议。通过对滇中易门县小街乡普家村-岔河水库剖面禄表组2个凝灰岩样品进行SHRIMP锆石U-Pb定年,获得禄表组凝灰岩的锆石206Pb/238U年龄为878.5±4.7Ma和878.0±4.0Ma,首次证实禄表组的形成时代为新元古代中期。禄表组凝灰岩SHRIMP锆石U-Pb年龄的获得,有利于正确认识昆阳群的划属关系,并为西南地区青白口纪地层格架的建立和对比提供可靠的年代学依据。

The Kunyang Group in the Central Yunnan Province, whose stratigraphic sequence and stratigraphic correlation are controversial, are always the research focus of Precambrian geology. Two zircon dating ages (878.5±4.7Ma and 878.0±4.0Ma) of tuff bedding from the Lubiao Formation in Yimen County are reported in this paper. Zircon dating of tuff bedding indicates that the formation occurred in Middle Neoproterozoic, which is the first report from the Lubiao Formation. Combined with a large number of high precision ages obtained from Kunyang Group, these stratigraphic ages provide important evidence for the acceptable division of Kunyang Group, and also offer reliable chronological data for the setting up of the Qingbaikou System in Southwest China.