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物源研究是理解黄土高原风成沉积物中古环境记录的关键一环。众多证据表明,黄土高原西北部的阿拉善高原及其周边广袤干旱地区是黄土高原黄土的主要风尘源区。但是,基于锆石U-Pb同位素地质年代学的证据对此提出了质疑。黄土高原黄土与青藏高原北部物质中的锆石具有相似的年龄分布,预示黄土高原风尘主要以西风搬运的方式来自青藏高原北部,特别是柴达木盆地。本研究通过分析西宁黄土的锆石年龄特征验证此假说。西宁处于在从青藏高原北部到黄土高原的假想搬运路线上。西宁黄土主要来自青藏高原北部的干旱区。西宁黄土中锆石的主要年龄分布与黄土高原黄土相似,反映青藏高原北部确实为黄土高原黄土的主要物质来源。但是,与黄土高原黄土相比,西宁黄土缺少年龄在360Ma左右和年龄小于100Ma的锆石。这两组年龄的锆石可能来自其他地区,例如处于中亚造山带。由于阿拉善干旱区也通过河流搬运接收来自青藏高原北部的物质,锆石U-Pb年龄证据并不能排除阿拉善干旱区作为主要风尘物源的可能。相反,阿拉善干旱区还接受来自其北部中亚造山带和其本身华北克拉通的物质,来自阿拉善干旱区的风尘可能更好地解释黄土高原黄土中的锆石年龄特征。
The study of provenance is a key part of understanding the paleoenvironment records of the aeolian sediments in the Loess Plateau. Numerous evidences show that the Alashan Plateau and its surrounding arid arid region in the northwestern Loess Plateau are the main sources of dust in the Loess Plateau. However, evidence based on zircon U-Pb isotopic geochronology is questioned. The zircons from Loess Plateau and northern Tibet Plateau have similar age distributions, indicating that the wind and dust transport in the Loess Plateau mainly comes from the northern part of the Qinghai-Xizang Plateau, especially the Qaidam Basin. This study validates this hypothesis by analyzing zircon age characteristics of Xining loess. Xining is on an imaginary handling route from the northern part of the Qinghai-Tibet Plateau to the Loess Plateau. Xining loess mainly comes from the arid area in the northern part of the Qinghai-Tibet Plateau. The main age distribution of zircon in Xining loess is similar to that of loess in the Loess Plateau, which shows that the northern part of the Qinghai-Xizang Plateau is indeed the main material source for the loess in the Loess Plateau. However, compared with loess in the Loess Plateau, Xining loess lacks zircons with ages of about 360 Ma and ages less than 100 Ma. The zircons of these two groups of ages may come from other areas, such as the Central Asian orogenic belt. As the Alashan arid region also receives material from the northern part of the Qinghai-Tibet Plateau by river handling, evidence of zircon U-Pb age does not exclude the possibility that the Alashan arid region may be the main dust source. In contrast, the Alashan arid region also receives material from the northern Central Asia orogen and its own North China craton, and the dust from the Alashan arid region may better explain the zircon age characteristics of the loess in the Loess Plateau.