青藏高原东北缘西宁黄土物源研究

Provenance study of the Xining loess in the Northeastern Tibetan Plateau,China

碎屑锆石U-Pb年代学被认为是研究沉积物物源的有效手段。然而,应用碎屑锆石U-Pb年代学对中国黄土高原进行物源研究时却获得了非常复杂的物源信息。西宁黄土沉积于青藏高原东北缘地区,对其开展碎屑锆石U-Pb年代学研究不仅可以获得其物源信息,同时可以为探讨青藏高原北缘碎屑物质对黄土高原的贡献提供重要依据。碎屑锆石形貌学研究结果表明其可能经历了强烈的物理风化以及多次再循环,同时也可能暗示了物源的高度复杂性。来自不同沉积层位的碎屑锆石U-Pb年龄结果表明,西宁黄土碎屑物质的最终来源可能是青藏高原北缘和中亚造山带,且物源区自约1.3 Ma以来可能没有显著变化,但是两者对西宁黄土的相对贡献可能在不同的时期具有微弱的差异。西宁黄土与中国黄土高原中、西部典型剖面的碎屑锆石年龄分布具有高度相似性,暗示了两者的物源区可能很大程度上具有一致性,但具少量差异。

Single-grain U-Pb dating of detrital zircons is regarded as an efficient and effective technique to differentiate the contribution of discrete sources.However,its application to the extensive Chinese Loess Plateau(CLP)yields rather complex information in provenance discrimination.The Xining loess was deposited in the Northeastern Tibetan Plateau(NETP),and the detrital zircon U-Pb chronology study can not only obtain provenance information but also provide an important basis to discuss the contribution of the detrital materials from the Northern Tibetan Plateau(NTP)to the CLP.Results of the detrital zircon morphology suggest that zircons may have undergone intense physical weathering and multiple recirculations,and may also indicate the high complexity of the source.Detrital zircon U-Pb age results from different sedimentary layers of the Xining loess reveal there are no obvious temporal variations in the provenance of the Xining loess since~1.3 Ma and materials may ultimately be eroded from the NTP and the Central Asian Orogenic Belt(CAOB),although the relative contribution of detritus from the two sources may slightly vary through time.The U-Pb age spectra of the Xining loess are highly similar to that of typical loess sites in the western-central CLP,suggesting that the provenance areas of the CLP and the Xining loess may be largely consistent,but the possibility of a small difference of provenance cannot be ruled out.