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.

大陆的大多数地壳都是由富含二氧化硅的侵入性火成岩制成的。 散装地球组成相对较差，大陆地壳与地球内部的平衡不处于平衡状态。 相反，大陆地壳是一种差异化产品，在数十亿年的地球历史上已经发展和发展。 在其他行星上似乎很少有硅质岩石，人们认为水在富含硅石的火成岩（如花岗岩）的形成和演化中起着重要作用。 花岗岩在表面以下形成公里。 花岗岩，流纹岩的火山对应物爆发为易于侵蚀的沉积物，几乎没有对大陆壳的持久贡献。 行星谜是为什么某些硅质岩浆爆发并形成短暂的流纹岩，而另一些则以深度结晶并形成花岗岩。 大陆壳的形成需要侵入性花岗岩，而不是表面的流纹岩。 水蒸气是流纹岩浆喷发的主要能源，水很可能在确定硅质岩浆是否会爆发并形成流纹岩，而不是在深度和形成花岗岩形成的花岗岩中起关键作用。 PI将通过研究Bishop Tuff Rhyolite的晶体和气泡的质地和组成来调查这一点，这是最详细研究的大型硅体。 在以前的工作中，他们发现在主教岩浆体的最早爆发的部分中，气体显然积聚。 气体的积累很可能会促进喷发，气体的积累需要相对于熔体的气泡运动。 气体在喷发前硅岩浆中积累的过程的程度和过程尚不确定。 PI将记录岩浆（浮石碎屑）中晶体运动和混合的程度，这些岩浆（浮石碎屑）在喷发前气体中均较弱且较差。 他们的工作将测试流纹岩岩浆稳定分层的想法（具有最小的混合），积聚气体并因此爆发。 相比之下，花岗岩岩浆可能会对流并释放累积的气体，因此最终在深度结晶并成为大陆壳的一部分。拟议的研究的更广泛影响包括芝加哥大学和俄勒冈大学研究生和本科生的参与。 学生将学习广泛的方法来根据现场和实验室的观察结果来开发和测试新概念。他们将学会使用许多复杂的技术，包括X射线断层扫描，红外光谱，阴极胶片固定成像和气孔图，并将有机会在国家会议上呈现其结果。