Collaborative Research: Phenocrysts and Bubbles in the Bishop Tuff Rhyolitic Magma

合作研究：主教凝灰岩流纹质岩浆中的斑晶和气泡

• 批准号: 0408615
• 负责人: Paul Wallace
• 金额: $ 3.96万
• 依托单位: University of Oregon Eugene
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-07-01 至 2006-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0408615&HistoricalAwards=false
• 关键词: Collaborative; Research; Phenocrysts; Bubbles; Bishop

Most of the crust of continents is made of intrusive igneous rocks rich in silica. The bulk earth composition is relatively silica poor and continental crust is not in equilibrium with earth's interior. Rather, continental crust is a differentiated product that has developed and evolved over billions of years of earth history. Silicic rocks appear to be rare on other planets, and it is thought that water plays an important role in the formation and evolution of silica-rich igneous rock such as granite. Granite forms kilometers below the surface. The volcanic counterpart of granite, rhyolite, erupts as deposits that are easily eroded and make almost no lasting contribution to continental crust. A planetary enigma is why some silicic magmas erupt and form ephemeral rhyolites whereas others crystallize at depth and form granites. The formation of continental crust requires intrusive granite, not surficial rhyolite. Water vapor is the main source of energy for eruption of rhyolitic magma and it is likely that water plays a key role in determining whether silicic magma will erupt and form rhyolite rather than crystallize at depth and form granite. The PI's will investigate this by studying the textures and compositions of crystals and bubbles in the Bishop Tuff rhyolite, one of the most thoroughly studied, large silicic bodies. In their previous work they found an apparent accumulation of gas in the earliest-erupted part of the Bishop magma body. It is likely that accumulation of gas facilitates eruption, and gas accumulation requires motion of bubbles relative to melt. The extent to which and process whereby gas accumulates in pre-eruptive silicic magma is uncertain. The PI's will document the extent of crystal motion and mixing within individual parcels of magma (pumice clasts) that were rich and poor in pre-eruptive gas. Their work will test the idea that rhyolitic magmas are stably stratified (have minimal mixing), accumulate gas and thus erupt. In contrast, granitic magmas may convect and release accumulated gas, and therefore, end up crystallizing at depth and becoming part of the continental crust. The broader impacts of the proposed study include the involvement of both graduate and undergraduate students at the University of Chicago and the University of Oregon. The students will learn a broad range of approaches to develop and test new concepts based on observations in the field and lab. They will learn to use a number of sophisticated techniques including X-ray tomography, infrared spectroscopy, cathodoluminescense imaging, and gas porisimetry, and will have an opportunity to present their results at national meetings.

大陆的大部分地壳是由富含硅的侵入火成岩构成的。 大部分地球的组成是相对贫硅和大陆地壳是不平衡的地球内部。 相反，大陆地壳是一种分化的产物，在数十亿年的地球历史中发展和演变。 硅质岩石在其他行星上似乎很少见，人们认为水在花岗岩等富含硅质的火成岩的形成和演化中起着重要作用。 花岗岩在地表下数公里处形成。 花岗岩的火山对应物流纹岩作为沉积物喷发，容易被侵蚀，几乎对大陆地壳没有持久的贡献。 行星之谜是为什么一些硅质岩浆喷发并形成短暂的流纹岩，而另一些则在深处结晶并形成花岗岩。 陆壳的形成需要侵入的花岗岩，而不是流纹岩。 水蒸气是流纹岩岩浆喷发的主要能量来源，水在决定流纹岩岩浆是否喷发形成流纹岩而不是在深部结晶形成花岗岩方面可能起着关键作用。PI将通过研究主教凝灰岩流纹岩中晶体和气泡的纹理和成分来调查这一点，主教凝灰岩流纹岩是研究最彻底的大型凝灰岩体之一。 在他们之前的工作中，他们发现在主教岩浆体最早喷发的部分有明显的气体聚集。 很可能是气体的聚集促进了喷发，而气体的聚集需要气泡相对于熔体的运动。 气体在喷发前岩浆中聚集的程度和过程尚不确定。 PI的将文件的结晶运动和混合的程度内的个别包裹的岩浆（浮石碎屑），丰富和贫穷的喷发前的气体。 他们的工作将检验流纹岩岩浆稳定分层（混合最少），积累气体，从而喷发的想法。 相比之下，花岗岩岩浆可能对流并释放积聚的气体，因此最终在深处结晶并成为大陆地壳的一部分。拟议中的研究的更广泛的影响包括芝加哥大学和俄勒冈州大学的研究生和本科生的参与。 学生将学习广泛的方法来开发和测试基于在现场和实验室观察的新概念。他们将学习使用一些复杂的技术，包括X射线断层扫描，红外光谱，阴极射线成像，气体孔隙度，并将有机会在国家会议上介绍他们的结果。