熊耳群火山岩系的上限年龄及其地质意义

The Upper Chronological Limit of Xionger Group's Volcanic Rock Series, and its Geological Significance

元古宙伸展构造环境产出的壳幔型熊耳群火山岩系 ,具有向碱性演化的趋势。晚期有石英正长斑岩、霓辉正长岩、正长辉长岩产出 ,赋存在熊耳群中上部。应用单锆石U Pb法测定年龄 ,石英正长斑岩谐和年龄为 ( 1731± 2 9)Ma ,霓辉正长岩、正长辉长岩上交点年龄分别为( 1644± 14)Ma、( 1750± 65)Ma。1650～ 170 0Ma是碱性岩浆活动热构造事件的标志 ,石英正长斑岩被中元古代晚期的高山河组不整合覆盖 ,故以 1650～ 170 0Ma作为熊耳群的上限。1650～ 170 0Ma热构造事件是华北地块重大地质事件 ,有可能是进一步划分中元古代重要的年龄界限。

The Crust mantle Mixed Type of volcanic series,Xionger Group, induced by Proterozoic extensional faulting tectonic environment, has an evolution trend towards alkali rock series. The late rocks such as quartz syenite porphyny, aegirine augite syenite and syenogebbro were hosted in the upper middle part of Xionger Group. By the single zircon U Pb dating method, the quartz syenite porphyny yielded an age of concordance (1 731±29)Ma, and the aegirine augite syenite and syenogebbro are dated upper cocordia intercept ages of (1 644±14)Ma and (1 750±65)Ma respectively (Table3,Fig.5), marking the event of alkali magmatic activites of time span 1650～1700 Ma. Because the quartz syenite porphyny was unconformably overlain by Gaoshanhe Formation, the time span 1 650～1 700Ma would be taken advantage of upper chronological limit for Xionger Group. The thermal structure event of 1 650～1 700 Ma was a tremeudous geological event for North China Massif as well as a important chronological limit in subdivision of Middle Proterozoic era.