Conditions for nanocrystals formation in Krafla shallow rhyolitic magma: A potential site for explosive eruptions

在IDDP项目框架下，地热勘探相关井在~2100 m深度发现Krafla流纹岩岩浆，为独特的岩浆储层研究开辟了新的可能性。Krafla岩浆钻探项目（KMDP）是ICDP优先项目的一部分，旨在了解Krafla火山口下岩浆的起源以及物理、化学和机械条件。然而，非常重要的是了解岩浆在什么条件下可能喷发，这是该项目旨在帮助解决的主要目标。本文提出的项目是基于最近关于纳米晶体对Krafla流纹岩岩浆和硅质岩浆脱气和粘度变化的影响以及这些纳米晶体对喷发爆炸性的影响的研究结果而产生的一个新想法。岩浆纳米晶体或“纳米石”是一种尚未被充分报道的现象，它已被证明对确定火山喷发中岩浆的爆炸性至关重要。然而，这些岩浆晶体形成和保持稳定的条件大多是未知的，因此有必要研究它们在克拉弗拉流纹岩岩浆中形成的能力，以了解可能引发的潜在爆炸性。该项目的总体目标是确定克拉弗拉火山喷发前和（潜在）同喷发岩浆中形成和维持岩浆纳米晶体所需的稳定场和条件，以及这些条件在岩浆性质中产生的变化。这将通过模拟Krafla岩浆储存条件的两种实验方法进行研究。形成和保持稳定的纳米岩所需的氧化态、压力、温度和时间将通过在岩浆冷却和可变P-T-t条件下使用Krafla流纹岩材料进行高度控制的结晶实验来确定。合成的材料将使用先进的方法进行精确分析，以确定纳米石结晶的存在、性质和程度。将进行流变学测量，以确定不同程度的纳米石结晶产生的粘度增加的程度。此外，将确定驱动岩浆中纳米石结晶的物理过程，即从均匀液体或非混相液体分离中结晶。初步研究表明，纳米岩可以在克拉弗拉的流纹岩岩浆中形成。然而，预计这个项目的主要成果是建立一个完整的纳米石结晶条件图，揭示这种岩浆的一个尚未被探索的关键方面。

Krafla rhyolitic magma encountered at ~2100 m depth by wells related to geothermal exploration, in the frame of the IDDP project, opened new possibilities for unique research on magma reservoirs. The Krafla Magma Drilling Project (KMDP), within the priority program ICDP, was created to comprehend the origin as well as the physical, chemical and mechanical conditions of this magma under Krafla caldera. However, of great importance is to understand under what conditions this magma may erupt, which is the main objective that this project aims to contribute to resolve.The project presented here is born as a novel idea based on recent results on the effect of nanocrystals on degassing and viscosity changes of Krafla rhyolitic magma, and silicic magma in general, and the implications for eruption explosivity these nanocrystals have. Magmatic nanocrystals or “nanolites” are a yet underreported phenomenon that has been shown crucial to determine explosivity of magma in volcanic eruptions. However, the mostly unknown conditions at which these magmatic crystals form and remain stable create the need to investigate their capacity to form in the rhyolitic magma at Krafla for the potential explosivity that may induce.The general objective of this project is to determine the stability field and conditions required to form and sustain magmatic nanocrystals in pre- and (potential) syn-eruptive magma of Krafla, and the changes that these produce in magma properties. This will be studied through two experimental approaches, mimicking the conditions at which Krafla magma is stored. The oxidation state, pressure, temperature and time required to form and keep stable nanolites will be determined by performing highly controlled crystallisation experiments during magma cooling and stabilisation at variable P-T-t conditions using Krafla rhyolite material. Resultant material will be precisely analysed using cutting-edge methods to determine the presence, nature and extent of nanolites crystallisation. Rheology measurements will be performed to determine the extent of viscosity increase produced by different degree of nanolite crystallisation. Additionally, the physical process driving nanolite crystallisation from magma will be determined, i.e. crystallisation from a homogeneous liquid or immiscible liquids separation.Preliminary work shows that nanolites can form in rhyolitic magma from Krafla. However, it is expected as a main outcome from this project to stablish a complete map of conditions suitable for nanolites crystallisation, unveiling a critical aspect of this magma not explored beforehand.