鄂北红安群黄麦岭组变沉积岩碎屑锆石年代学及地质意义

Detrital-Zircon Geochronology for the Metasedimentary Rocks of Hong′an Group Huangmailing Formation in the Northern Hubei and Its Geological Significance

鄂北红安群的层序与时代是一个长期存在争议的问题,而其中黄麦岭组含磷岩系形成时代问题则是这些争议中的焦点。通过对红安群黄麦岭组含磷岩系中变沉积岩中的LA-ICP-MS锆石U-Pb法测年,结果表明：（1）黄麦岭组变沉积岩中,介于874～709 Ma时间段的年龄点成为了黄麦岭组变沉积岩中主要的碎屑锆石年龄组成,峰值为807 Ma,表明新元古代形成的岩浆岩是黄麦岭组最重要的物源;（2）最年轻的岩浆锆石年龄为709 Ma,表明形成岩石的主要沉积作用应晚于该时间;（3）碎屑锆石年龄谱系对比分析发现,黄麦岭组形成时代应晚于随县群沉积时期;（4）剖面上岩石组合测年结果表明,以大磊山地区为代表的红安群,表现为总体无序的构造岩石单位叠置,并以包含了青白口纪（晋宁造山过程中）的物质记录而区别于随县群和武当群。

The sequence and forming age of Hong′an Group in the Northern Hubei were debated for a long time.The focus of this debate is the formation time of Huangmailing Formation phosphorus-bearing metasedimentary rocks.This study analyses the LA-ICP-MS zircon U-Pb dating data of Hong′an Group Huangmailing Formation phosphorus-bearing metasedimentary rocks.The results revealed that（1）the age between 874-709 Ma,with a peak of 807 Ma,makes up primary detrital-zircon age composition,which supports the idea that Neoproterozoic magmatite is foremost provenance of the Huanmailing Formation;（2）the minimus magmatic zircon of all the detrital-zircon from the metasedimentary rocks is 709 Ma,which manifests that the main sedimentation of the Huangmailing Formation should be later than the time;and（3）Compared with Suixian Group,the forming age of Hong′an Group should be later according to the detrital zircon age spectrums;（4）The results of dating for different rocks in the Daleishan section reveal that Hong′an Group is characterized by superimposition of overall disorder tectonic rock unit and contains the material record during Jinningian orogenic processes,which makes the Hong′an Group different from the Wudang Group and Suixian Group.