东秦岭商丹地区武关岩群变沉积岩碎屑锆石U-Pb年龄及其地质意义

摘要

笔者以东秦岭商丹地区武关岩群毛坪长英质片岩单元中黑云石英片岩为研究对象,进行碎屑锆石LA-ICP-MS U-Pb年代学研究,探讨其沉积时代及物质来源.结果显示,碎屑锆石年龄可以划分为4个年龄谱段:早古生代年龄谱段416.8~590.5Ma,峰值为449Ma;新元古代年龄谱段731.5~1 055.8Ma,峰值为830Ma;中元古代-古元古代年龄谱段1 606.9~1 816.9Ma,峰值为1 804Ma;古元古代-新太古代年龄谱段2 434.6~2 690.3Ma,峰值为2 687Ma.综合研究认为,武关岩群毛坪长英质片岩单元的沉积岩形成时代不早于420Ma,形成于顶志留世商丹洋闭合阶段,是构造混杂并卷入原有的裂谷型火山-沉积岩系之中的时代较新的沉积地层,其碎屑物质可能由北秦岭构造带和南秦岭构造带共同提供.%The biotite quartz schist from the Maoping felsic schist unit in Wuguan Group of Shangnan-Danfeng tectonic belt has been selected as research object in this paper, which has been studied by usingLA-ICP-MS zircon U-Pb isotope chronology to discuss the sedimentary age and material source of this schist.The results show that the detrital zircon ages can be divided into 4 age spectrums: Early Paleozoic-Early Simian age spectrum ranges from 416.8Ma to 590.5Ma, with a peak of 449Ma;Neoproterozoic age spectrum varies from 731.5Ma to 1055.8Ma, peaking in 830Ma;Mesoproterozoic-Early Proterozoic age spectrum changes from 1 606.9Ma to 1 816.9Ma, with a peak of 1 804Ma;Proterozoic-Archen age spectrum are 2 434.6 ~2 690.3Ma, peaking in 2 687Ma.The comprehensive study suggests that, the formation time of Maoping felsic schist unit from Wuguan Group is notolder than 420Ma, which was formed in the closure stage of formed in Shangdan ocean in Silurian and served as tectonic melange and new sedimentary formation involved in the original rifted volcanic-sedimentary rocks, while the detritus source would be provided from both north and south Qinling structural belts.