黄土高原物质来源及冰期-间冰期物源变化的碎屑锆石和独居石U-Pb年代学证据

Provenance and its variation of the Loess Plateau in China during glacial-interglacial periods: Evidence from detrital zircon and monazite U-Pb chronology

  • 摘要: 本研究旨在通过多矿物年代学分析揭示黄土高原碎屑物质主要来源及其在冰期-间冰期的物源差异。其中选取了黄土高原潜在物源区柴达木盆地、黄河上游沉积物和毛乌素沙漠现代沉积物,以及西峰剖面相邻层位黄土(L5和L9)和古土壤(S5和S9)样品开展碎屑锆石和独居石U-Pb定年测试,统计对比周源造山带基岩独居石年代学结果,并开展碎屑年龄分布的对比。研究发现,黄土高原碎屑独居石主要年龄峰值与青藏高原北部的地质记录相匹配,但与华北克拉通和阿尔泰山的特征年龄组分差异较大;冰期黄土和间冰期古土壤的碎屑锆石U-Pb年龄分布没有明显的规律性差异,但独居石U-Pb年龄分布显示一定的差异。依据结果可知,碎屑独居石U-Pb分析对黄土高原不同来源的粉尘具有较强的鉴别能力,黄土高原碎屑物质主要起源于青藏高原北部,并可能经柴达木盆地和/或中部沙漠最终沉降至黄土高原;黄土-古土壤的碎屑独居石来源差异可能反映了冰期-间冰期大气环流格局的变化。

     

    Abstract: To reveal the provenance and its changes of the Loess Plateau in China (LP) during the glacial and interglacial periods, multi-mineral U-Pb geochronology analysis was conducted. The potential source areas of LP, including the modern sediments of the Qaidam Basin, upper reaches of the Yellow River, the Mu Us Desert, the loess (L5 and L9) and paleosoil (S5 and S9) layers of the Xifeng section, were sampled for detrital zircon and monazite U-Pb dating. The monazite U/Th-Pb age data from the periphery orogenic belt were compared statistically with the detrital monazite age of this study. Results show that the main age peaks of detrital monazite of the LP match the geological records of the northern part of the Tibet Plateau, but significantly differ from the major age components of the North China Craton and the Altai Mountains. There is no obvious difference in the age distribution of detrital zircon U-Pb in glacial loess and interglacial paleosoil, but the age distribution of monazite U-Pb shows certain differences. This study indicated that U-Pb analysis of detrital monazite is able to discriminate the dust contributions from different potential sources of the LP. The dust source of the main-part LP was originated from mainly the northern part of the Tibet Plateau and might transport to the plateau through the Qaidam Basin and/or the central desert. The differences in the source of detrital monazite in loess and paleosoil may reflect the changes in the atmospheric circulation pattern during the glacial and interglacial periods.

     

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