青藏高原地区宇生核素暴露年代数据存在问题探讨

Discussion of Existing Problems on the Terrestrial Cosmogenic Nuclides Exposure Ages of Xizang( Tibetan) Plateau

青藏高原是第四纪古冰川研究的理想区域也是宇宙成因核素(terrestrial cosmogenic nuclides,TCN)暴露测年技术应用的天然实验场所。然而,现有的TCN测年数据与先前学者基于其他测年手段的研究结果不一致,显得相对年轻。为了探索其原因,本文尝试对青藏高原1594个TCN测年数据进行统计分析。研究结果表明:1测年样品中97%的样品是漂砾样品,测年数据中约有93%的年代数据小于130 ka;2 280组(n≥3)漂砾样品年代数据中大约76%的漂砾组数据变异系数大于10%,而基岩和羊背石样品组测年数据变异系数较低、相对集中;3冰碛垄表面漂砾样品的不等时暴露与后期侵蚀可能是造成TCN年代数据结果偏年轻的主要原因。本研究可为青藏高原地区冰川地貌TCN暴露年代研究提供重要启示。

The Tibetan Plateau is an ideal region for Quaternary glacier research and an excellent natural laboratory for terrestrial cosmogenic nuclides TCN exposure dating. However, the TCN 10Be exposure ages were younger than previous research results based on other dating methods. In order to explore the reasons, we have analyzed 1594 TCN 10Be exposure ages of the Tibetan Plateau. The results suggest that： （1） 97% samples were boulders and about 93% exposure ages were less than 130 ka; （2） About 76% of the 280 boulder groups have the variation coefficient of exposure age larger than 10%. However, the cofficient for bedrock groups and roche moutonnee group are small. （3） The reasons for TCN exposure ages underestimate the morianes age can be ascribed to incomplete exposure and erosion. This study can provide an important inspiration for TCN exposure dating of glacial landforms in Tibetan Plateau.