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

克拉夫拉岩浆减压：从静止的岩浆糊到爆炸性的泡沫？

基本信息

批准号：
298792151
负责人：
Professor Dr. Donald Bruce Dingwell
金额：
--
依托单位：
Sektion Mineralogie, Petrologie und Geochemie
依托单位国家：
德国
项目类别：
Infrastructure Priority Programmes
财政年份：
2016
资助国家：
德国
起止时间：
2015-12-31 至 2021-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/298792151?language=en
关键词：
Decompression Krafla magma immobile mush

项目摘要

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.

IDDP-1表明，在Krafla火山口下约2公里深处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，还是只是从超固质felsite进入钻孔的熔融渗出液？如果侵入物是在上次喷发时形成的，为什么它没有喷发呢？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项目所建议的科学计划中。本研究的两个中心目标是：(1)限制流纹岩岩浆的总体反应，特别是克拉弗拉岩浆对缓慢减压的反应（在浅层）。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)约束流纹岩岩浆在挤压和张拉（减压）两种作用下向围岩的运移。提出的方法是基于独特的实验室实验，探索流纹岩岩浆在与KMDP相关的P-T条件下缓慢减压的可能情况。将研究几种类型/组成的硅酸盐熔体（“岩浆”），从水合标准玻璃开始，合成硅酸盐熔体与IDDP-1的流纹岩和Krafla最后一次流纹岩喷发的天然和水合黑曜岩的主要成分，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范围内绘制，从“无”到轻微成核到爆炸发泡和碎裂，使我们能够限制Krafla岩浆的可喷发性。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felite（易碎，不破碎）紧密地置于流纹岩岩浆之上，然后两者将缓慢减压，迫使岩浆与felite相互作用，以响应减压。第二种方法是利用高t、高负荷的单轴压力机。圆柱形岩浆样品在较大的金属夹套圆柱形felsite样品内，将在与KMDP相关的温度下经受加载和卸载/减压事件。相互作用将探索使用断层扫描和（微）纹理技术。总之，这些方法将允许限制硅酸盐熔体和felite之间的相互作用和熔体的流动性，分别。这里提出的研究预计将为理解岩浆如何在浅层地壳中产生、演化和相互作用以及它们如何对干扰（例如钻探）作出反应提供关键答案。