川西北高原的地貌垂直地带性与寒冻夷平面

Vertical Geomorphologic Zonation in the Northwest Sichuan Plateau and Freezing Planation Surface

川西北高原地貌垂直地带性明显：流水地貌带,＜3 800 m；冰缘地貌带,3800～4200 m；冰川地貌带,＞4200 m；相应的主导地貌过程分别是流水侵蚀,冻融侵蚀和冰川侵蚀。本文提出了高原面形成的寒冻夷平机制,并认为川西北高原是大面积构造隆升背景下形成的寒冻夷平地貌。花岗岩和石灰岩等结晶岩抗寒冻风化能力强,形成了冰川发育的高山；三叠系砂板岩,抗寒冻风化能力差,形成了融冻土流发育的丘状起伏的高原面。此外,还延伸联想到青藏高原夷平面和高原隆升的一些科学问题,如冻融侵蚀在高原地貌形成和演化中的作用,地面隆升幅度与地壳构造上升幅度,高原面高度的区域差异和大冰盖问题等。

Vertical geomorphologic zoningin the Northwest Sichuan Plateau is obvious and elevations for different geomorphologic zones are ： fluvial zone, 〈 3 800 m ; glacial margin zone, 3 800 - 4 200 m; glacial zone, 〉 4 200 m. A freezing planation mechanism is proposed to explain formation of the plateau surfaces and the Northwest Sichuan Plateau is freezing planation geomorphology, which is formed undertectonic uplift conditions in a large area. In the plateau, the high glacial mountains are usually underlain by crystalline rocks of granite and limestone while the hilly plateau surfaces are underlain by Triassic epimetasediment rocks of sandstone and slate, because crystalline rocks have higher strength against freezing weathering than epimetasediment rocks. In addition, a few of scientific questionson planation surfaces and uplifting of Tibet Plateau are also discussed in this paper, such as the function of freezing planation in the plateau formation and evolution, the magnitudes of plateau surface elevation increase and of tectonic uplifting in the plateau, ragional differences of plateau surfaces , and the giant ice caps.