Decompression of Krafla magma: From immobile magma mush to explosive foaming?

IDDP-1表明，非喷发脱气流纹岩熔体存在于约2公里的深度下Krafla火山口，提出了许多问题，如：是否有真正的岩浆在IDDP-1，或只有一个熔融软泥进入钻孔hypersolidus felsite？如果侵入体是在上次喷发时形成的，为什么没有喷发？最终，这一发现和由此产生的问题引发了KMDP。该提案的目标与KMDP的几个核心目标密切相关，也体现在成功的KMDP项目中建议的科学计划中。这一建议的两个核心的、协同的相互关联的目标是：（1）限制流纹岩岩浆的一般响应，特别是克拉弗拉岩浆对缓慢减压（在浅深度）的响应。这包括气泡是否、何时以及如何成核和生长、渗透性网络的形成，以及可能的岩浆破碎等问题。(2)在挤压和张性（减压）状态下，限制流纹质岩浆向周围寄主岩石的流动性。所提出的方法是基于独特的实验室实验，探索可能的情况下，流纹质岩浆的反应，在P-T条件下缓慢减压KMDP相关。将研究硅酸盐熔体（“岩浆”）的几种类型/成分，从水合标准玻璃开始，合成硅酸盐熔体，主要成分为IDDP-1流纹岩和Krafla最后一次流纹岩喷发的天然和水合黑曜石，最后是KMPD井的Krafla天然流纹岩岩浆（如果获得）。岩浆对缓慢减压的反应将在800-920°C和16-55 MPa的范围内进行映射，从“无”到轻微的成核到爆炸性发泡和破碎，使我们能够限制Krafla岩浆的喷发性。Krafla岩浆的流动性将通过两种方法进行探索：第一种方法是将可渗透的Felsite（脆性，非碎裂）紧紧地放置在流纹岩岩浆上方，然后缓慢减压，迫使岩浆与Felsite相互作用以响应减压。第二种方法利用高温、高负荷单轴压力机。一个更大的圆柱形岩浆样品内，金属护套的圆柱形Felsite样品将受到相关的温度KMDP加载和卸载/减压事件。将使用层析成像和（微）纹理技术探索相互作用。这些方法一起将允许分别约束硅酸盐熔体和长石之间的相互作用以及熔体的流动性。这里提出的研究预计将提供关键的答案，以了解岩浆如何产生，演变和相互作用在地壳浅层，以及它们将如何对干扰，例如钻井反应。

IDDP-1 demonstrated that non-eruptively degassed rhyolite melt is present at about 2 km depth under Krafla Caldera, raising many questions, as: Is there true magma in IDDP-1, or only a melt ooze that entered the borehole from hypersolidus felsite? If the intrusion formed during the last eruption, why did it not erupt? Ultimately this finding and the questions arising from it triggered KMDP. The objectives of this proposal are intimately linked to several core objectives of the KMDP and also manifested in the scientific program suggested in the successful KMDP-project. The two central, synergetically interlinked objectives of this proposal are: (1) to constrain the response of rhyolitic magma in general, and Krafla magma in special to slow decompression (in shallow depths). This encompasses the questions if, when and how bubbles will nucleate and grow, the formation of permeable networks, and possibly magma fragmentation. (2) To constrain the mobility of rhyolitic magma towards surrounding host rocks in compressional and tensional (decompression) regimes. The proposed approach is based on unique laboratory experiments, exploring possible scenarios as the rhyolitic magma responses to slow decompression under P-T conditions relevant to KMDP. Several types/compositions of silicate melts ('magma') will be studied, beginning with hydrated standard glass, synthetic silicate melts with the major components of the rhyolite from IDDP-1 and natural and hydrated obsidian from the last rhyolitic eruption of Krafla, finally Krafla natural rhyolitic magma from KMPD-well (in case obtained). The magma response to slow decompression will be mapped in the range of 800-920°C & 16-55 MPa, from 'nothing' to minor nucleation to explosive foaming and fragmentation, enabling us to constrain the eruptability of Krafla magma. The mobility of Krafla magma will be explored by two approaches: In the first, a permeable felsite (brittle, non-fragmenting) will be tightly placed above the rhyolitic magma then both will be slowly decompressed forcing the magma to interact with the felsite in response to decompression. The second approach makes use of the high-T, high-load uniaxial press. A cylindrical magma sample inside a larger, metal-jacketed cylindrical felsite sample will be subjected at temperatures relevant to KMDP to loading and unloading/decompression events. The interactions will be explored using tomography and (micro-)textural techniques. Together these approaches will allow constraining interaction between silicate melt and felsite and the mobility of the melts, respectively. The research proposed here is expected to provide answers critical for understanding how magmas are generated, evolve and interact in the shallow crust as well as how they will react upon disturbance as for instance drilling.