基于锆石U-Pb年龄的洛川黄土物源示踪  

Tracing the provenance of Luochuan loessbased on zircon U-Pb ages

作　　者：王苗苗 弓虎军[1] WANG Miaomiao;GONG Hujun(Department of Geology,Northwest University,Xi′an 710069,China)

机构地区：[1]西北大学地质学系,陕西西安710069

出　　处：《西北大学学报（自然科学版）》2021年第4期695-708,共14页Journal of Northwest University（Natural Science Edition）

基　　金：国家自然科学基金资助项目(201170022)。

摘　　要：利用锆石U-Pb定年方法对洛川黄土-古土壤剖面的10个层位(S0、L1、L2、S2、L15、L18、L22、L24、L29、L33)进行研究,以获得各层位锆石年龄组合。结果发现,大约以1.25 Ma为界,剖面上段沉积(S0、L1、L2、S2、L15)与剖面下段沉积(L18、L22、L24、L29、L33)存在明显的年龄差异,并且通过与黄土高原周边潜在物源区锆石年龄组合的对比,发现剖面上段的沉积物主要来自西北部的阿拉善地区及西毛乌素沙漠,剖面下段的沉积物主要来自于北部的东毛乌素沙漠。研究后认为,研究区1.25 Ma左右的剖面物源发生变化时,刚好对应于一次地球轨道尺度事件,此时的黄土高原粉尘物源应该发生由北向西北的转变,同时也指示了东亚冬季风应该发生由北向西北偏转,且这次冬季风的转变从L18开始至L15结束,是一次过渡性的转变,而非突变。In this study,zircon U-Pb dating method was used to determine 10 layers(S0,L1,L2,S2,L15,L18,L22,L24,L29,L33)of the Luochuan loess-paleo soil profile in order to obtain zircon age combinations of each horizon.The results show that the sediments in the upper sections(S0,L1,L2,S2,L15)are significantly different from those in the lower sections(L18,L22,L24,L29,L33)with the boundary of about 1.25Ma.Compared with the zircon age combination of potential provenances around the Loess Plateau,it is found that the sediments in the upper sections of the profile mainly come from the Alxa areas and the western Mu Us desert in the northwest,while the sediments in the lower sections of the profile mainly come from the eastern Mu Us Desert in the north.The source change of profile just corresponds to an earth orbit-scale event about 1.25Ma.At this time,the dust provenance in the Loess Plateau may change from north to northwest,which also indicates that the East Asian winter monsoon may deflect from north to northwest,and the change of the winter monsoon starts from L18 to L15,which seems a transitional change rather than a sudden change.

关 键 词：洛川黄土 锆石U-PB年龄 物源示踪 

分 类 号：P66[天文地球—地质学]