Unperlitized Obsidian Expansion: Hydration and Formation Characteristics

Abstract

Magma-water interaction is defined as one of the most important parameters determining the explosivity of volcanic eruptions. However, accurately quantifying the water content in volcanic products formed during syn-eruptive or post-eruptive processes remains a significant challenge. This study investigated the thermal expansion and decomposition behavior of obsidian sampled from the Nevşehir Acıgöl Maar, which was subjected to heat treatment without exhibiting perlitic texture development, in order to elucidate the underlying mechanisms and characteristics of the process. The physical and chemical changes that the banded obsidian experienced during its expansion were analyzed using various analytical methods. In this context, FT-IR analysis was used to observe modifications in water components. The mass loss in the sample was quantified using the TG-DTA method, while the textural changes occurring during the obsidian expansion experiment were determined through three-dimensional tomographic imaging technique. The results show that thermal decomposition of volcanic glass involves the release of volatiles and both primary and secondary water species across a range of temperatures. This study demonstrates experimentally that hydrous rhyolitic obsidian can generate vesicles that expand at varying rates, particularly in regions where water and volatiles are loosely bound within the glass structure.

Keywords

• obsidian
• hydration
• expansion
• FTIR
• TGA-DTA
• computed tomography

Perlitleşmemiş Obsidiyen Genleşmesi: Hidrasyon ve Oluşum Özellikleri / Unperlitized Obsidian Expansion: Hydration and Formation Characteristics

Abstract

Magma ile su etkileşimi, volkanik patlamalarda patlamanın şiddetini belirleyen en önemli parametrelerden biri olarak tanımlanmaktadır. Bununla birlikte, patlama ile oluşan volkanik ürünlerde rastlanılan su içeriğinin volkanizma sırasında veya sonrasında gelişip gelişmediğinin belirlenmesinde çeşitli kısıtlamalar bulunmaktadır. Bu çalışma, Nevşehir Acıgöl Maar’ından örneklenen obsidiyenin, perlitik doku sahibi olmadan ısıl işlem ile genleşmesinin nedeni ve özellikleri ile termal ayrışma özelliklerinin belirlenmesi amacıyla gerçekleştirilmiştir. Bantlı obsidiyenin genleştirilmesi sırasında geçirmiş olduğu fiziksel ve kimyasal değişimler, çeşitli analitik yöntemler ile incelenmiştir. Bu kapsamda, su bileşenlerinde meydana gelen değişimler FT-IR analizi ile gözlemlenmiştir. Örnekte gerçekleşen kütle kaybının değeri TG-DTA yöntemi ile ölçülmüş olup genleştirme deneyi sonucunda oluşan üründe genleşmeye bağlı meydana gelen dokusal değişimler üç boyutlu tomografik görüntüleme tekniği ile belirlenmiştir. Sonuç olarak bir volkan camının termal olarak ayrışması, uçucu gazlar ile birincil ve ikincil su türlerinin farklı sıcaklıklarda çeşitli süreçler sonucunda salınması ile meydana gelmektedir. Bu çalışma ile su içeren riyolitik bileşime sahip obsidiyenin, su ve uçucu bileşenlerin kimyasal olarak gevşek bir şekilde bağlandığı yerlerde çeşitli oranlarda genişleyen gözenekler oluşturabildiği deneysel olarak gösterilmiştir.

Keywords

• obsidiyen
• hidrasyon
• genleşme
• FTIR
• TGA-DTA
• bilgisayarlı tomografi

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