EAGER: Investigating the possibility of low temperature (<700 C) melt in silicic igneous systems

地壳是如何由硅质岩浆形成的，以及像黄石公园这样的大型火山是如何喷发的，这些问题几个世纪以来一直困扰着地质学家。该项目将包括从观测到的火山岩中收集新的地球化学数据，并进行实验室实验，以评估这一有争议的假设，即500至550摄氏度的岩浆在硅质熔体的形成和喷发中发挥作用。该项目有可能改变人们对硅质岩浆系统如何运作的看法，并产生潜在影响，包括大陆地壳如何形成，硅质岩浆为什么喷发，以及矿床是如何形成的。该项目将培养一名研究生，并开发一种新的冷密封系统中的温度梯度装置，这将使其他实验岩石学家受益。这一勘探项目建立在最近的一项发现之上，即含水的过碱性熔体可以在低于标称火成岩固相线(700摄氏度)的温度下与石英+长石共存。为了评价这种低温熔体存在并在硅质岩浆喷发中起作用的可能性，提出了三项任务：1)通过释放压力从1kb到0.3kb，并与已知的相平衡进行比较，来评价与石英和长石平衡的低温熔体的减压作用：2)利用1kb压力的冷封容器研制热梯度装置；3)比较鱼峡谷凝灰岩矿物分离物中U、Fe和Si的矿物内同位素比率，以评估是否可以辨别花岗岩和硅质火山岩的形成之间的联系。这一奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

The questions of how Earth's crust was made by silicic magmas, and how large volcanoes like Yellowstone erupt, have perplexed geologists for centuries. This project will include collecting new geochemical data from observed volcanic rocks and performing laboratory experiments aimed at assessing the controversial hypothesis that magmas at temperatures of 500 to 550 degrees C play a role in making and erupting silicic melts. The project has potential to make transformative change on views of how silicic magma systems operate with potential impacts including how the continental crust forms, why silicic magmas erupt, and how ore deposits form. This project will train a graduate student, and develop a new device for thermal gradients in a cold seal system that will benefit other experimental petrologists. This exploratory project builds upon the recent finding that hydrous peralkaline melts can coexist with quartz + feldspar at temperatures below the nominal igneous solidus (700 degrees C). Three tasks aimed at assessing the possibility that this low temperature melt exists and plays a role in eruption of silicic magmas are proposed: 1) Assess the role of decompression of low temperature melt in equilibrium with quartz and feldspar by releasing pressure from 1 kb to 0.3 kb and comparing to know phase equilibria; 2) Develop a thermal gradient apparatus using cold seal vessels at 1 kb pressure; 3) Compare the intra mineral isotope ratios of U, Fe and Si from mineral separates of the Fish Canyon Tuff to assess if connections between the making of granites and silicic volcanic rocks can be discerned.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.