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浙江缙云县大洋山石鼓尖花岗岩坑穴成因 总被引：3，自引：0，他引：3
浙江缙云县大洋山石鼓尖海拔1477m,在其山顶花岗岩表面发现大量直径几十厘米至1m左右、深度10cm至45cm的坑穴。经对60处坑穴的形态量测发现,坑穴主要发育在山坡的NE和SE一侧;坑穴积水后出水口流向亦主要朝向NE和SE。对岩石标本的偏光显微镜和X荧光光谱鉴定分析发现,该处基岩为易风化、泥化明显的中细粒钾长花岗岩。该处年平均气温9.2oC,年降水量在1700mm以上,每年12月至翌年3月会经历4个月日气温在0oC上下波动的冰缘作用期,雨雪水冻融交替对基岩的崩解作用明显。该处位于夏季台风雨迎风坡（NE和SE坡）一侧,暴雨常伴随有10级以上大风。现场常可见风力吹蚀带动坑穴中细岩屑对坑穴内壁产生加速旋转磨蚀作用。上述研究表明,该处花岗岩坑穴形成的主要动力成因首先是冰缘寒冻风化作用,暴雨和山顶大风的风力吹蚀加速了坑穴的形成。观察表明,此种作用目前仍在进行之中,风向的转变是造成坑穴出现多种形态的主要原因。由于此处海拔距雪线尚有1500m高差,即使在第四纪盛冰期也仅是接近雪线高度,且因山顶无积雪屯冰的低洼地形,因此,第四纪“冰臼”成因说难以成立。 相似文献
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On top of Shigujian Peak (1477 m a.s.l.) of the Dayangshan Mountain in Jinyun County, Zhejiang Province, large amounts of
granite pits with diameters ranging from several dozens of centimeters to around one meter and depth from 10 cm to 45 cm are
found on rock surface. These pits mainly appear on the NE and SE sides, and their drainage mouths are in the same direction.
The identification results through micropolariscope and X-ray fluorescence spectrometer reveal that bedrock of pits is from
middle to fine-grained moyite being apt to be weathered and modified. In Dayangshan region the annual mean temperature is
9.2°C and annual precipitation is over 1700 mm. On the one hand, there always experiences a period of periglacial action with
temperature oscillating near 0°C for 4 months, i.e., from December to March next year. As a consequence, the freezing-thawing
cycles may be remarkable to disintegrate the bedrock. On the other hand, the windward slope of Shigujian Peak meets typhoon
of over force 10 on the Beaufort scale in summer, therefore, the blowing makes suspending sands or pebbles grind in swirling
form. Based on field investigation and periglacial geomorphic theory, the pits on top of Shigujian Peak are attributed to
freezing-thawing of periglacial action. Meanwhile, storm and strong wind accelerate the process. Observation shows that both
the actions are still undergoing and variant directions of wind are the main cause for making different shapes of the pits.
Because the top of Shigujian is 1500 m lower than the present snow line, some scholars considered that “glacial pothole” formed
in the Quaternary is hard to work, even though in the Last Glacial Maximum (LGM).
Foundation: Regional landform and landscape survey programme of the Zhejiang Institute of Geological Survey
Author: Zhu Cheng (1954–), Professor, specialized in geomorphology and the Quaternary geology. 相似文献
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