喜马拉雅降水势能与剥蚀强度时空对应的定量研究

Quantitative research on temporal and spatial coupling of precipitation potential energy and erosion intensity in Himalayas

在活动造山带的研究中，剥蚀作用被认为与大气降水有着密切的关系，并且越来越多的研究证据发现，气候因子在山脉的演化中承载了重要的影响力，降水被认为是活动造山带剥蚀作用的动因。研究者用降水量和剥蚀强度的对应来阐释气候对山脉演化的制约。然而也有学者提出反面例证来否定降水量与山脉剥蚀强度之间的耦合关系，进而否定气候因子在活动造山带构造演化中的影响。由此而提出的科学问题是：降水究竟与剥蚀强度有没有关联？降水怎样影响剥蚀强度，遵循怎样的机理？在详细分析活动造山带剥蚀作用过程和机理的基础上，本文提出了降水势能的概念，在校验和整合TRMM降水量数据与ETOPO-1数字地貌数据体之后，计算了喜马拉雅造山带的降水势能空间分布。同时，收集整理了喜马拉雅造山带内已公开发表的磷灰石裂变径迹（AFT）年龄数据，以此为数据库获取了喜马拉雅剥蚀强度时空分布格局。通过这两个数据体的定量分析，研究发现，喜马拉雅造山带内，剥蚀强度与降水势能之间有很好的空间耦合性。这说明，在喜马拉雅构造带，现今的AFT年龄空间分布，是受气候作用主导的。进一步的研究发现，喜马拉雅带大约2．8Ma以来的AFT年龄与现今的降水势能秩相关性显著，且有局部最优的线性相关性，说明喜马拉雅带的剥蚀空间分布受第四纪以来很年轻的地质历史时期的地表降水过程所控制。最新的气候样式决定了现今的降水过程，控制了造山带剥蚀强度的空间分布。

Erosion has belts. More and been more thought to have evidence imply a close relation with precipitation in active orogenic that climatic factors play an important role in orogenevolution and precipitation has been thought the motivation causing erosion in orogenic belts. Usually, researchers explain the climatic constraints on mountains evolution with the coupling relationship of precipitation and erosion intensity. Nevertheless, some others raise the evidence to deny the coupling relationship and further more to deny the significant influence of climate on orogenic belts evolution. So here is the question, whether precipitation is associated with erosion intensity？ How does precipitation influence erosion and what mechanism is it？ In this paper, based on analysis of orogenic belts erosion process and mechanism, we put forward the precipitation potential energy （PPE）concept and draw the spatial distribution map of PPE in Himalayas. Meanwhile, we collect almost entirely apatite fission track （AFT）age data, and obtain the spatial distribution of AFT ages in Himalayas. According to quantitative analysis of these two databases, we found that erosion intensity related to PPE distribution is much better than precipitation spatial distribution. Furthermore, AFT age and PPE has significant spearman relationship for samples since 2.8 Ma. This imply that significant erosion process in Himalayas was caused in young geological period by precipitation, especially since the Quaternary. Global cooling since Cenozoic era resulted in erosion strengthening, and the latest climatic pattern decided the erosion spatial distribution in active orogenic belts.