湖北宣恩县麻阳寨晚奥陶-早志留世龙马溪组斑脱岩LA-ICP-MS 锆石 U-Pb 年龄及其地质意义

摘要

There are several clay beds recognized from in the lower part of the Longmaxi Formation as the top of the Wufeng Formation in the sduty area.They are deposited from volcanic tuffaceous material,and then rock formation for al-teration.In order to further understand the Yangtze region Ordovician-Silurian volcanic event at the turn of the age,the authors are LA-ICP-MS zircon U-Pb dating for the clay beds recognized from the two Late Ordovician-Early silurian Long-Maxi Creek Group sectional.The results show LA-ICP-MS zircon U-Pb dating of the clay beds recognized(450.0 ±3.6) Ma,published by the International Commission on Stratigraphy Ordovician-Silurian boundary consistent Age(443.7 ± 1.5)Ma,belong to the Late Ordovician.Compared with the stratigraphic units in the study area in the north and south in the obtained bentonite zircon ages are earlier time limit on the period,it has important significance to begin to explore the volcanic activity.%研究区内奥陶纪龙马溪组中下部（即相当于原五峰组上部—顶部层位）发育多个因火山凝灰质物质沉积、蚀变形成的粘土岩层，为了进一步认识上扬子地区奥陶纪—志留纪之交的火山事件年龄，对湖北高罗麻阳寨地区晚奥陶—早志留世龙马溪组剖面的斑脱岩进行了LA-ICP-MS锆石U-Pb定年，获得加权平均年龄为（450.0±3.6） Ma，与国际地层委员会发布的奥陶系—志留系界线年龄（443.7±1.5） Ma近似，同属晚奥陶世。相较研究区北部和南部获得的同地层单位中的斑脱岩锆石年龄均较早，对探讨该时期火山活动开始的时限具有重要意义。