日本樱岛火山灰玻璃碎屑形态特征研究

The surface texture features of volcanic glass shards in Sakurajima, Japan

火山灰年代学是控制地层年代最简单可靠的直接手段，近年来在磁性地层、构造演化和古气候环境、考古等研究中被广泛重视和应用，经常成为最关键的要素。然而对其在地层中的识别常常产生较大分歧，制约了对年代的控制及与此相关的许多科学问题的解决。火山玻璃作为火山灰中的常见和标签物质，是识别火山灰最直接可靠的材料。日本强烈的第四纪火山活动和清晰连续的火山灰沉积在这方面具有代表性。本文利用光学显微镜和扫描电镜，对日本樱岛第四纪晚期典型火山灰中的火山玻璃形态和表面结构特征进行观察分析，总结出火山玻璃碎屑的外部形貌为独特、醒目的各种玻璃碎片状，呈各种大小和形态的带有气子L的曲面或弧面尖棱角状颗粒，如锋利的长条状、各种多边形粒状、片状（月牙状、三角状、多边形状等）和三交面状等，表面特征为各种与火山喷发炸裂作用相关的光滑或弱贝壳状断口的曲面，及与火山喷气有关的各种孔洞、管槽、小圆坑、椭圆形坑和眼状坑。其中眼状坑和三交面状这两种特殊表面形态分别只在安山质和流纹质火山灰中出现，为准确识别中，酸性火山灰及其类型提供了微观形态学鉴定标志。

recognition of volcanic ash in stratigraphy often causes heated debate, hindering a reliable age determination and a resolution of many related scientific problems. Volcanic glass as a common and characteristic component in the ash is the key criteria to identity volcanic ash. In this paper, we try to use the surface texture features of the volcanic glass shards from the typical volcanic ashes in Sakurajima, Japan by using optical and scanning electron microscopes. The results show that the characteristics of volcanic glass are fractured shapes （long strip, sheet, granular, trihedral faces, etc.） with sharp edges, curved surfaces and various kinds of holes, pipe grooves, small round pits, oval pits and eye-like pits that are related to volcanic eruption. This provides an independent microscopic morphology approach to distinguish precisely andesitic and rhyolitic volcanic ash.