Integrated studies on Himalayan uplift and climatic changes - A case of Kathmandu Nappe

我们从跨学科的角度，如地质学、沉积学、磁地层学、花粉和硅藻分析、地貌学和冰川学，研究了尼泊尔中部晚中新世以来的隆升过程以及由此产生的气候和环境变化，包括加德满都盆地，加德满都盆地位于加德满都推覆体上，是喜马拉雅地区的古气候档案。主要研究结果如下：加德满都推覆体由一个单一的逆冲板组成。它被下伏的中央主冲断带所包围，并在北部被逆序冲断所切割，这导致了北喜马拉雅上第三纪中新世以来的快速隆起。主中央逆冲带在9 ~ 6Ma以前为韧性逆冲带，但在3 Ma以后为脆性正断层。建立了上上新世至更新世古加德满都湖沉积地层，并阐明了其沉积相的垂向和横向变化。但这种变化究竟是由山体隆起引起的，还是由气候变化引起的水位波动引起的，目前还没有定论。明确了加德满都盆地沉积环境和古气候的变化。花粉分析表明，加德满都地区在25 ka前后比现在更冷、更干燥。Paloe-Kathmandu湖是最大的湖泊，在30 ka左右，其最高岸线高度可达海拔1440米，然后逐渐降低。末次盛冰期加德满都以南亚喜马拉雅地区的气温比现在低7 ~ 8℃，也比现在干燥。此后气候逐渐变暖，为循环湿润气候，并在5 ka左右形成现在的气候。在加德满都盆地进行了三次钻探，深度分别为221米、65米和5米。

We studied uplift processes and the resultant climatic and environmental changes since the Late Miocene in central Nepal including the Kathmandu basin, which is located on the Kathmandu Nappe and is archives of paleoclimate in the Himalaya, from interdisciplinay viewpoints such as geology, sedimentology, magnetostratigraphy, pollen and diatom analyzes, geomorphology and glaciology.Main results are as follows:1. Kathmandu Nappe consists of a single thrust sheet. It is edged by the underlying Main Central Thrust zone and cut on the north by an out-of-sequence thrust which has resulted in the rapid uplift since the latest Miocene of the Higher Himalaya to the north.2. The Main Central Thrust zone has been a normal fault in brittle condition since 3 Ma, although it has been thrust zone in ductile condition until 9 〜 6Ma.3.The stratigraphy of the upper Pliocene to Pleistocene Paleo-Kathmandu lake deposits has been established and the vertical and lateral changes of their sedimentary fades have been elucidated. But it is still unsolved whether the changes has been caused by mountain uplift or by fluctuation of water-level due to climatic changes.4. The changes of the sedimentary environment and paleoclimate in the Kathmandu basin has been made clear.5. The pollen analysis shows that the Kathmandu area has been cooler and more dry than the present around 25 ka.6. The Paloe-Kathmandu lake has been the largest with a maximum shore-level upto 1440 m above sea level around 30 ka and then has been gradually reduced.7. The temperature at the Last glacial maximum in the Sub-Himalaya to the south of Kathmandu was 7-8℃ lower and more dry than the present. Thereafter it has been gradually warm with cyclic humid climate and became to the present climate around 5 ka.8. Three borings upto 221 m, 65 m and 5 m depth were performed in the Kathmandu basin.