利用陆面岩石中生成的宇生同位素重建冰川漂砾运动历史的尝试

冰川漂砾的形成年代通常难以直接测定，并且漂砾形成以后是否被再次搬运或者移动过，更是无法知道。本文研究发现，通过测试砾石不同部位的宇生同位素，不仅可以测定砾石形成的时代，而且可以确定砾石再次被搬运或者被翻转的年代，从而恢复砾石运动的历史。本文以石英中生成的宇生同位素^10Be，对青藏高原东南部海子山的冰川漂砾进行了探讨，结果表明该砾石形成于倒数第二次冰期(186～128ka BP之间)，在末次冰期中再次被冰川搬运，使之反转。该方法不局限于^10Be和冰川漂砾，也适用于其他陆面岩石中生成的宇生同位素以及其他成因的石块或者砾石。因此为探讨冰川作用、泥石流活动、重力崩塌等过程提供了一种重要的方法和技术途径。

Reconstructing the History of Drift Boulders' Movement by Using the Autochthonous Cosmogenic Isotope ~(10)Be

The ages of drift boulders are usually very difficult to be dated directly, and it is harder to know whether the boulders have been re-transported or rolled over since their formation. The authors think that not only the formation chronology but also the re-transportation history of boulders can be determined by measuring the cosmogenic isotopes at different parts of the boulders. A case study has been carried out on a drift boulder by using the isotope 10Be. Based on the measurement and analyses of the cosmogenic isotope 10Be of a drift boulder, which is located in the vicinity of Haizishan in the southeastern margin of the Qinghai-Tibet Plateau, we may conclude that the boulder was formed during the glacial stage before the last (186~128 ka BP) and was re-transported and rolled over during the last glacial stage. There have been at least two stages of glacial development since 200 ka BP in the vicinity of Haizishan, corresponding to Stage 6 and Stages 4~2 of the deep-sea oxygen isotopes, respectively. This method, using other cosmogenic isotopes as well, can be applied to stone blocks or gravels formed by other agents. Therefore, it provides an important method to study glacial processes, activities of debris flow and rock collapse etc.