江西九江中更新世红土物质来源研究

Provenance Tracing of Middle Pleistocene Red Earth in the Jiujiang Area,Jiangxi Province

华南地区广泛分布中更新世红土。目前,对其物质来源尚有争议。九江红土剖面的沉积时代已得到很好限定,同时由于其沉积连续、地层出露较好,是开展中更新世红土物质来源研究的理想剖面。通过对九江中更新世红土2件碎屑锆石样品的分析,共获得177颗谐和锆石U-Pb年龄,主要峰值集中在新元古代(816 Ma、801 Ma和991 Ma)、古元古代(2019 Ma、2022 Ma和2481 Ma)和新太古代(2502 Ma),并具有不显著的中生代峰值(135 Ma)。将其与潜在远源和近源物源区的锆石U-Pb年龄组成进行对比,结果发现中国北方戈壁、沙漠和黄土高原、塔里木盆地、华北平原并不是九江中更新世红土的主要源区。庐山北麓早更新世发育的洪积扇为九江中更新世红土发育提供了充足物质。九江中更新世红土和九江晚更新世黄土的碎屑锆石U-Pb年龄组成存在明显差别,后者主要来自长江河漫滩的碎屑物质。不同的气候条件主导了九江地区红土和黄土的发育,二者都受控于青藏高原构造隆升产生的环境变化。

The Middle Pleistocene red earth is widely distributed in South China.However,its source areas remain controversial.The sedimentary age of the Jiujiang red earth profile has been defined well in previous studies,and it is an ideal region for studying the source of the red earth material in the Middle Pleistocene due to its continuous deposition and good exposure.Through the analysis of two detrital zircon samples from the Middle Pleistocene red earth in Jiujiang,we obtained 177 concordant zircon U-Pb ages.The peak ages are mainly concentrated in the Neoproterozoic(816 Ma,801 Ma,and 991 Ma),Paleoproterozoic(2019 Ma,2022 Ma,and 2481 Ma),and Neoarchean(2502 Ma),with an insignificant peak age in the Mesozoic(135 Ma).The results show that the Gobi Desert,northern deserts,Loess Plateau,Tarim Basin,and North China Plain in northern China are not the main source regions of the Middle Pleistocene red earth in Jiujiang.The Early Pleistocene diluvial fan at the northern piedmont of Lushan Mountain provided sufficient materials for development of the Middle Pleistocene red earth in Jiujiang.The detrital zircon U-Pb age compositions of the Middle Pleistocene red earth are different from those of the Late Pleistocene loess in Jiujiang.Different climatic conditions dominated the development of the red earth in the Middle Pleistocene and the loess in the Late Pleistocene in the Jiujiang area,but both of them were sedimentary responses to environmental changes caused by the tectonic uplift of the Tibetan Plateau.