论文部分内容阅读
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。
The clastic rocks of the Shujiaba Group in the Devonian Shujiaba area in the west Qinling Mountains are taken as the research object. The U-Pb age of detrital zircons is studied by LA-ICP-MS, and the formation age, provenance composition and tectonic setting are discussed. The mean age-weighted mean of the minimum zircon age group was 413 Ma, which represents the lower limit of deposition of Shujiaba group. The paleo-biological data of previous studies limited the formation age to the Middle Devonian. The ages of detrital zircons obtained can be divided into four bands: Sinian - Palaeozoic age band 619 ~ 409Ma, peak value 445Ma; Neoproterozoic age band 930 ~ 735Ma, peak 849Ma; Mesoproterozoic age spectrum Segment 1760 ~ 1033Ma; Neoarchean - Palaeogeographic age band 3095 ~ 2478Ma. The comprehensive study shows that the source of Shujiaba Group is diverse, including the tectonic belt in the northern margin of the West Qinling, the eastern section of the North Qilian orogenic belt and the base of the North China Plate. The eastern section of the North Qilian orogenic belt and the northern margin of the West Qinling Is the main source area for the deposition of Shujiaba Group, and the latter is the dominant one. Combined with the regional geological data, according to the provenance of its provenances, the Shujiaba Formation is transformed into a local rift basin in the extensional environment after continental-continental or arc-continental collision.