Formation processes of tafoni on pyroclastic rock surfaces with hydrothermal alteration on the Isotake coast, Shimane, Japan
Formation processes of tafoni on pyroclastic rock surfaces with hydrothermal alteration on the Isotake coast, Shimane, Japan
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日本岛根岛矶海岸热液蚀变火山碎屑岩表面塔福尼的形成过程
DOI：
10.1016/j.geomorph.2021.108050
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发表时间：
2022
期刊：
影响因子：
3.9
通讯作者：
Abe Yutaka
中科院分区：
文献类型：
--
作者：
Kogure Tetsuya;Sueyoshi Ryuya;Ohira Hiroto;Sampei Yoshikazu;Shin Ki-Cheol;Abe Yutaka
日本岛根县等竹海岸的悬崖有两种不同颜色的独特表面，有塔福尼和没有塔福尼，尽管它们由相同的火山碎屑岩组成。导致严重事故的落石只发生在没有塔福尼的地表。通过对岩壁材料的地球化学分析和施密特锤回弹试验，阐明了盐风化在塔弗尼地层形成中的作用过程。tafoni后壁上方解石的锶稳定同位素比值（87Sr/86Sr）为0.706298，说明该方解石中的钙来源于岩壁物质，但岩壁通过溅水吸收海水。碳、氢、氮和硫元素分析和x射线衍射图显示，热液蚀变形成的斜发沸石在含有tafoni的悬崖表面比不含tafoni的悬崖表面更丰富，这表明钙的丰度较高，可以掺入方解石中。在任何表面类型中，随着斜沸石含量的增加，峭壁材料的硬度增加。因此，虽然热液蚀变也强化了表面，但塔方尼优先形成于热液蚀变产生丰富斜沸石的表面。我们的研究结果表明，塔福尼的存在表明岩崩的总体风险较低。
Cliffs along the Isotake coast, Shimane, Japan, have two types of distinctive surfaces with different colours, with tafoni and without tafoni, even though they consist of the same pyroclastic rock. Rockfalls, which result in severe accidents, occur only on the surface without tafoni. Geochemical analyses of the cliff materials and the Schmidt hammer rebound test were conducted to elucidate the process of salt weathering in the formation of tafoni. The strontium stable isotope ratio (87Sr/86Sr) of the calcite (i.e., 0.706298) found on the backwall of tafoni indicated that the calcium in this calcite is derived from cliff materials, although the cliff receives seawater through splashing. Carbon, hydrogen, nitrogen and sulfur elemental analyses and X-ray diffraction pattern measurements revealed that clinoptilolite formed by hydrothermal alteration was more abundant in the cliff surfaces with tafoni than in those without tafoni, indicating a high abundance of calcium available for incorporation into calcite. The hardness of the cliff materials increases as the clinoptilolite content increases in any surface type. Consequently, tafoni preferentially form on surfaces with abundant clinoptilolite produced by hydrothermal alteration, although the surfaces have also been strengthened by hydrothermal alteration. Our results imply that the presence of tafoni indicates an overall lower risk of rockfalls.