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

IDDP-1证明，在克拉夫拉火山口地下约2公里深的地方存在非喷发脱气流纹岩熔体，这引发了许多问题，如：IDDP-1中是否存在真正的岩浆，或者只是从超固体长石进入钻孔的熔体渗出？如果侵入体是在上次喷发时形成的，为什么它没有喷发？最终，这一发现和由此引发的问题引发了KMDP。这项提案的目标与KMDP的几个核心目标密切相关，也体现在成功的KMDP项目所建议的科学计划中。这一提议的两个相互关联的中心目标是：(1)总体上限制流纹岩岩浆的反应，特别是克拉岩浆对缓慢减压(浅层)的反应。这包括气泡是否、何时以及如何成核和生长、可渗透网络的形成，以及可能的岩浆破碎等问题。(2)限制流纹岩岩浆在挤压和拉张(减压)状态下向围岩的迁移。提出的方法是基于独特的实验室实验，探索流纹质岩浆在与KMDP相关的P-T条件下对缓慢减压做出反应的可能情景。将研究几种类型/组成的硅酸盐熔体(‘岩浆’)，首先是水合标准玻璃、合成硅酸盐熔体，主要成分来自IDDP-1流纹岩和来自Krafla最后一次流纹岩喷发的天然和水化黑铁矿，最后是来自KMPD井的Krafla天然流纹岩岩浆(如已获得)。岩浆对缓慢减压的响应将被绘制在800-920°C和16-55兆帕的范围内，从“零”到轻微成核到爆炸性泡沫和破碎，使我们能够限制克拉夫拉岩浆的喷发能力。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长石(脆性的、不破碎的)紧密地放置在流纹岩岩浆之上，然后两者都将被缓慢减压，迫使岩浆与长石相互作用以响应减压。第二种方法是利用高温、高负荷的单轴压力机。在一个更大的、包裹着金属的圆柱状长石样品中的圆柱状岩浆样品将在与KMDP相关的温度下经受加载和卸载/减压事件。将使用断层摄影术和(微观)纹理技术来探索相互作用。这些方法结合在一起，将分别限制硅酸盐熔体和长石之间的相互作用和熔体的流动性。这里提出的研究有望提供关键的答案，以了解岩浆是如何在地壳浅层产生、演化和相互作用的，以及它们将如何对干扰做出反应，例如钻探。

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.