库布齐沙漠碎屑锆石U-Pb年龄组成及其物源分析
西北大学大陆动力学国家重点实验室, 西安 710069
中国地质调查局西安地质调查中心, 西安 710054
中国科学院地球环境研究所, 黄土与第四纪国家重点实验室, 西安 710061
国家自然科学基金项目（批准号：40802039、201180025、41372020和41372036）资助
中图分类号:P597+.3;P941.73
State Key Laboratory of Continental Dynamics, Northwest University, Xi'an 710069
Xi'an Center of Geological Survey, China Geological Survey, Xi'an 710054
State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710061
库布齐沙漠的物源一直存在很大的争议，并存在周缘山脉侵蚀、就地起沙、黄河补给等诸多观点。碎屑锆石U-Pb年龄谱是物源示踪的有效手段。本研究在野外考察的基础上，通过对比沙漠不同地区地表沙及其潜在物源碎屑锆石的U-Pb年龄谱解析库布齐沙漠的物源。本研究采集了包括河套古湖的滨湖相细砂、沙漠底部基岩、黄河及其二级支流河道砂、沙丘表面沙等在内的9个样品，测试了其中900粒碎屑锆石的U-Pb年龄；同时还测定了2个古滨湖相样品的光释光年代。结果显示，库布齐沙漠碎屑锆石U-Pb年龄主要有5个谱峰，分别为2.5Ga、1.9Ga、960Ma、450Ma和280Ma，且在沙漠内部显示一定的空间分带性。其中3个沙漠沙样品显示了>1.4Ga的古老锆石组分从自西向东逐渐增加的现象（KD-1：34.4%；KD-3：42.4%；KD-8：56.8%）；同时， < 450Ma的年轻锆石存在自西向东逐渐减少的现象（KD-1：41.6%；KD-3：40.2%；KD-8：28.4%），这可能反映了库布齐沙漠东部地区本地物质的贡献大，而库布齐沙漠西部地区黄河沉积物的贡献较大。湖盆干枯后经风化剥蚀产生的沙粒，以及黄河携带的泥沙为库布齐沙漠提供了主要物质，湖泊、河流和风力活动在沙漠形成过程中可能各自扮演了重要的角色。
Hobq Desert is located at the north of Yimeng Uplift of Ordos Plateau, facing the Hetao Plain. So the terrain is relative low in the north and high in the south. It is surrounded by the Yellow River from the east, north and west, and with narrow banding shape of east-west direction. It is 400km in length from east to west and 20~30km and 100km in width from north to south for the east and west part, respectively. The provenance of the Hobq Desert is still under great debates with views of ranging from erosion of surrounding mountains to desertification of local bedrocks, and to material supply from the Yellow River. The U-Pb age of detrital zircon is a powerful tool for source tracing. Totally 900 zircon grains from 9 samples, including 3 surface aeolian sand, 2 lake shore sand, 2 modern river bed sand and 2 Mesozoic sandstone, were collected to correlate the U-Pb ages provenance to trace the possible source of the Hobq Desert. The 2 samples from paleo-lake were dated by OSL and have age of 62.1±8.9ka for KD-2 and 22.4±2.4ka for KD-4, which can be compared to the Hetao paleo-lake exposed below the desert. The results show that zircon U-Pb ages of the Hobq Desert sand are mainly distributed around 2.5Ga, 1.9Ga, 960Ma, 450Ma and 280Ma. The zircon age distribution show obvious spatial variation pattern, which reflect eastward decreasing contribution (KD-1:41.6%, KD-3:40.2% and KD-8:28.4%)of < 450Ma peaks from the Yellow River and accordingly increasing contribution(KD-1:34.4%, KD-3:42.4% and KD-8:56.8%) of >1.4Ga peaks from local sandstone material. The Hetao paleo-lake may have played an important role in mixing and holding the local source and the Yellow River contribution together for the eastern desert, which may be eroded and contribute the mixed material to the eastern Hobq Desert after its dying. By contrast, the western desert is sourced more from Yellow River contribution. In all, paleo-lake, rivers and wind activities have played their own roles in the formation of Hobq Desert.
图 1研究区数字高程图和采样位置
研究区数字高程图和采样位置
Figure 1.DEM map of the studied area and the sampling sites.
DEM map of the studied area and the sampling sites.
图 2库布齐沙漠KD-2和KD-4湖相沉积剖面
库布齐沙漠KD-2和KD-4湖相沉积剖面
Figure 2.The lake sections of KD-2 and KD-4 of Hobq Desert
The lake sections of KD-2 and KD-4 of Hobq Desert
图 3代表性样品KD-4的剂量恢复实验结果
代表性样品KD-4的剂量恢复实验结果
Figure 3.Results of dose recovery tests of the representative sample KD-4
Results of dose recovery tests of the representative sample KD-4
图 4KD-4 (a)和KD-2 (b)样品的De值雷达分布图
KD-4 (a)和KD-2 (b)样品的De值雷达分布图
Figure 4.Radial plot of De values for samples of KD-4 (a)and KD-2 (b)
Radial plot of De values for samples of KD-4 (a)and KD-2 (b)
图 5样品的锆石U-Pb年龄谱图
样品的锆石U-Pb年龄谱图
Figure 5.Zircon U-Pb age population of the samples.
Zircon U-Pb age population of the samples.
图 6非度量多维标度分析图(MDS)
非度量多维标度分析图(MDS)
Figure 6.Non-metric multi-dimensional scaling(MDS)plots.
Non-metric multi-dimensional scaling(MDS)plots.
表 1样品信息
样品信息
Table 1.Sample details
Sample details
表 2OSL测年结果
OSL测年结果
Table 2.The results of OSL dating
The results of OSL dating
Ludwing K R. Isoplot v. 3.0:A Geochronological Toolkit for Microsoft Excel. Berkeley Geochronology Center Special Publication, 2003
图(6)
表(2)
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DEM map of the studied area and the sampling sites.
The lake sections of KD-2 and KD-4 of Hobq Desert
Results of dose recovery tests of the representative sample KD-4
Radial plot of De values for samples of KD-4 (a)and KD-2 (b)
Zircon U-Pb age population of the samples.
Non-metric multi-dimensional scaling(MDS)plots.