哀牢山构造带两侧上志留统-下泥盆统碎屑锆石年代学:物源及其构造意义

Geochronology of Detrital Zircon from the Upper Silurian-Lower Devonian Sedimentary Rocks at both Sides of the Ailaoshan Tectonic Zone: Provenance and Geological Significance

哀牢山古特提斯洋的打开时限及其缝合带的具体位置对理解哀牢山古特提斯洋构造演化具有非常重要的意义。本文采用碎屑锆石年代学方法,分析了哀牢山构造带及其两侧不同时期沉积物源的特征及其变化,解译了其物源差别所指示的哀牢山古特提斯洋盆打开时限以及缝合带的构造位置。碎屑锆石年代学显示,哀牢山构造带两侧上志留统碎屑锆石都记录一个~450 Ma的最年轻的峰值和一个格林威尔期造山事件的年龄群(1100~800 Ma),以及一个2600~2400 Ma的次峰;不同于上志留统,构造带东侧下泥盆统碎屑锆石并未出现年轻的~450 Ma峰值年龄信息,西侧U-Pb年龄分布模式与上志留统一致,记录~450 Ma峰值年龄信息,而且构造带两侧下泥盆统碎屑锆石的2600~2400 Ma的峰值明显要强于上志留统。区域上发表的碎屑锆石年代学资料,也揭示相同的年龄峰值。因此,综合区域上的其他地质资料,我们认为哀牢山古特提斯洋盆的打开时限应该在晚志留世-早泥盆世,哀牢山断裂带代表了哀牢山洋盆闭合的位置。

Constraining the precise time of opening and location of the suture of the Ailaoshan Paleotethys is crucial tobetter understand the tectonic evolution of the whole Paleotethys in Southwest China.In this contribution,we carriedout a systematic U-Pb analysis of detrital zircon to provide insights into the provenance of sedimentary materials,temporal variation,and their geological significance.The dating results of detrital zircon grains from the UpperSilurian-Lower Devonian sedimentary sandstones from both sides of the Ailaoshan tectonic zone show that all theUpper Silurian detrital zircon grains are characterized by a similar youngest age peak at ca.450Ma and two subordinateage populations including the Greenville orogenic events(1100-800Ma)and the2600-2400Ma age group.Detritalzircon grains in the Lower Devonian rocks gave similar age populations with an exception of those from the east side ofthe Ailaoshan tectonic zone lack the youngest age peak at ca.450Ma.In addition,the detrital zircon grains in the LowerDevonian rocks display age peak at2600-2400Ma more significant than the Upper Silurian ones.By comparison withthe published dating data of detrital zircon,a common characteristic with same age populations has also been revealed.Integration with the regional geological data,we propose that the opening of the Ailaoshan Paleotethys Ocean tookplace during the Late Silurian to Early Devonian and the Ailaoshan Fault should represent the location of thePaleotethys suture zone.