摘要:
应用LA-ICP-MS单颗粒锆石U-Pb定年方法, 对柴达木盆地北缘乌兰县上泥盆统牦牛山组两组砂岩样品开展了碎屑锆石U-Pb年代学研究。测年结果显示年龄值分布较宽, 可以划分为5个峰值年龄区间。在这些碎屑锆石中, 最小的年龄为407.9 Ma, 属于岩浆成因, 限定了该套地层的沉积下限, 为不早于早泥盆世末期, 结合区域地质与古生物资料, 该套地层为晚泥盆世。碎屑锆石的年龄分布表明本区可能存在五期区域性地质构造事件, 其中早古生代最为突出, 其次为新元古代和古元古代早期—新太古代晚期, 暗示这三期岩浆活动和变质作用较为活跃, 并为本套地层提供了主要的锆石来源, 具有多时代混合物源特征。样品中少量太古代碎屑锆石的谐和度较好, 为研究区附近可能存在太古宙古老地层提供了一定证据, 但仍需进一步研究。
Abstract:
This paper studied the age distribution of detrital zircons of sandstone in Maoniushan Formation of Upper Devoion of Wulan country from northern margin of Qaidam Basin using LA-ICP-MS U-Pb isotopic age of zircons. The results show that the detrital zircons of sandstone has a wide range of zircon age, which can be divided into 5 peak interval. This sequence of the strata possibly was deposited in the Late Devonian and not earlier than the end of Early Devonian according to the regional geological correlation and paleontological data. The age distribution of detrital zircons indicate that there may be events of five regional geological structure in this area, and the most prominent is the Early Paleozoic, followed by Neoproterozoic and Early Paleoproterozoic-Late New Archean, which imply that the three periods of metamorphism and magmatic activity is relatively active and provide the main source of zircon for this strata with a mixture of multi-source characteristics. The obtained age data indicate the multi-provenance of the sandstone. In addition, there are less Archean detrital zircon having a high degree of harmony, which has provided some basis for the possible existence of Archean old strata, but needs further research.
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