西秦岭舒家坝地区泥盆纪舒家坝群碎屑锆石LA-ICP-MS U-Pb年龄：源区特征与形成时代

摘要

Choosing the Shujiaba Group detrital rocks in Shujiaba area as the study object and using LA-ICP-MS zircon U-Pb isotope chronology, the authors studied the sedimentary age and material source of the Shujiaba Group. 413Ma, the mean of the minimum ages group, indicates that the sedimentary age of Shujiaba Group should be the Middle Devonian. Four groups can be recognized from the zircon ages spectrum:Sinian-Early Paleozoic age group (619~409Ma), with the peak value of 445Ma;Neopro-terozoic age group (930~735Ma), with the peak value of 849Ma; Mesoproterozoic age group (1760~1033Ma); and Paleoproterozo-ic-Neoarchaen age group (3095~2478Ma). The age group information indicates that the material sources were mainly derived from North Qilian orogenic belt ,the northern margin of West Qinling tectonic zone and the basement of North China block, of which the North Qilian orogenic belt and the northern margin of West Qinling tectonic zone made the major contribution, with the last one playing the leading role. The material source features and regional geology suggest that the Shujiaba Group was formed in a rifted basin resulting from the transitional tectonic setting from syn-collision (compressional setting) to post-collision (extensional setting).%以西秦岭舒家坝地区泥盆纪舒家坝群碎屑岩为研究对象，进行碎屑锆石LA-ICP-MS U-Pb年龄研究，探讨其形成时代、物源组成和构造背景。所测样品最小锆石年龄组的年龄加权平均值为413Ma，代表了舒家坝群的沉积下限，结合前人研究的古生物资料将其形成时代限定为中泥盆世。所获碎屑锆石年龄可划分为4个谱段：震旦纪-古生代年龄谱段619~409Ma，峰值为445Ma；新元古代年龄谱段930~735Ma，峰值为849Ma；中元古代年龄谱段1760~1033Ma；新太古代-古元古代年龄谱段3095~2478Ma。综合研究认为，舒家坝群的物源具多元性，包括西秦岭北缘构造带、北祁连造山带东段和华北板块基底，其中北祁连造山带东段和西秦岭北缘构造带是舒家坝群沉积的主要物源区，且后者占主导地位。结合区域地质资料，根据其物源组成特征判断，舒家坝群形成于陆-陆或弧-陆碰撞后由挤压转换为伸展环境的局部裂陷盆地。