火山玻璃风化层的透射电镜研究

TEM STUDY OF WEATHERED LAYERS ON THE SURFACE OF VOLCANIC GLASS

利用透射电镜（TEM）和X射线能谱（EDX）研究了长白山天池火山1000年和4000年前两次大喷发产生的火山玻璃风化层特征。TEM分析显示，4000年前大喷发浮岩中的火山玻璃风化层平均厚度3.7 mm，1000年前大喷发浮岩中的火山玻璃风化层平均厚度为1.0 mm。EDX分析显示，两次大喷发浮岩中的火山玻璃风化层化学组成与火山玻璃相比富Al、Fe，而Si减少。火山玻璃风化层富Al发生在Al的浓度较高的中到弱酸溶液中（pH=5-6），火山玻璃表面形成含有少量的非晶质的Al、Si、Fe物质，这些非晶质的次生物质是火山玻璃风化早期阶段形成的。天池火山喷发物中火山玻璃的微观特征的差异可能与火山喷发年代和喷发后的环境有关，研究天池火山不同期次喷发物中火山玻璃的微观特征具有一定的理论和实际应用价值。

TEM ＋ EDX analyses revealed the surface characteristics and thickness of the weathered layers on the volcanic glass in pumice. The results showed that the average thickness of the weathered layers on the volcanic glass from volvanic eruption （1000 B. P. ） is 1.0 mm.. For the eruption （4000 B. P. ） the average thickness of the weathered layers on the volcanic glass is 3.7mm, These features indicate that the thickness of the weathered layers on the volcanic glass from the Tianchi volcano is related with the ages of volcanic eruption. Therefore, they can be used as indicators for the determination of a sequence of volcanic eruptions. The EDX analyses also showed that the weath- ered layers on the volcanic glass contain increased A1 and reduced Si in chemical composition with respect to the vol- canic glass itself. It is inferred that such a change should have occurred in a low-temperature setting and a nearly neutral to weakly acidic solution. Hence, it is well as their environments based on a systematic dera. possible to identify the dates and sequences of volcanic eruptions as study of micro characteristics of eruptive materials in the Tianchi caldera.