Collaborative Research: An Experimental and Analytical Investigation of the Parameters That Influence Measured CO2 in Plagioclase-Hosted Melt Inclusions in MORB

合作研究：对影响 MORB 斜长石熔体包裹体中 CO2 测量值的参数进行实验和分析研究

• 批准号: 1634211
• 负责人: Robert Bodnar
• 金额: $ 7.81万
• 依托单位: Virginia Polytechnic Institute and State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-09-01 至 2019-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1634211&HistoricalAwards=false
• 关键词: Collaborative; Research; Experimental; Analytical; Investigation

Volcanoes are major Earth features and, when they erupt, can cause significant damage to life, infrastructure, and ecosystems. When they occur on the seafloor, they can also trigger tsunamis that have the potential to cause devastating damage to coastal communities. Thus, our understanding of magmatic processes is important for both understanding how the Earth works as well as for helping us understand the dangers magmatic events and volcanic eruptions can cause. This research focuses on the story about magmatic processes that occur deep in the Earth as told by tiny inclusions of melt trapped in crystals of plagioclase, one of the most ubiquitous minerals in the Earth's crust. Up until now, melt inclusions in plagioclase have not been considered reliable archives of primary information for volatile geochemical species like H2O, CO2, or S due to diffusion and post entrapment leakage. There have also been questions about the origin of melt inclusions and when and where they form in the history of the plagioclase in which they occur. This research combines innovative laboratory experiments and comprehensive controlled calibration studies to reconstruct the original volatile composition of melt inclusions in plagioclase from ultra-phyric lavas erupted on the seafloor in the Pacific Ocean on the Juan de Fuca Ridge, just west of the Washington and Canadian border. The experiments will be done on both plagioclase and coexisting olivines from the same suite of samples to compare against one another and assess the degree to which post entrapment crystallization and the process of reheating impact the measured volatile content of the inclusions. Time-series experiments will be conducted on a heating stage at various temperatures (from 1200 C to 1270 C) and heating rates. Analyses of the major element composition of the inclusions will be carried out via electron microprobe; trace element compositions will be determined using laser inductively coupled mass spectrometry; Fourier transform infrared spectroscopy will be used to verify CO2 and H2O compositions of large inclusions; and the ion microprobe and micro-Raman spectroscopy will be used to analyze CO2, H2O, S, and Mg. The proposed experiments that will be carried out will determine the mechanisms by which volatiles are lost from inclusions during transport in the crust or during experimental heating via process such as diffusion, formation of bubbles, and leakage through cracks in the crystal. Goals of the research are to produce better measurements of the depth of mineral crystallization from magmas in mid-ocean ridge environments for both olivine and plagioclase. Questions to be addressed include how post entrapment crystallization in the inclusion and the formation of bubbles affect the measured volatile contents of the melt inclusions; how different homogenization methodologies and quench rates influence measured volatile contents; what the measured values of different volatile species indicate about the depth of formation of the crystal cargo and the CO2 budget of the ocean crust; and how does the information from plagioclase melt inclusions compare to that coming from olivine melt inclusions. Broader impacts of the work include development of new experimental techniques that have potential implications to other fields, societal impacts in terms of better understanding volcanic processes and understanding magmatically generated ore deposits. It will also involve the training of two graduate students and two undergraduates.

火山是主要的地球特征，当它们爆发时，可能会对生命，基础设施和生态系统造成重大破坏。 当它们发生在海底时，它们还可以触发海啸，这些海啸可能会对沿海社区造成毁灭性损害。 因此，我们对岩浆过程的理解对于理解地球的运作方式以及帮助我​​们了解危险的岩浆事件和火山喷发可能引起的危险至关重要。这项研究的重点是关于地球上深处发生的岩浆过程的故事，这是由于斜线晶体中的微小融合物所表明的，这是地壳中最普遍的矿物质之一。 到目前为止，由于扩散和夹带后泄漏，尚未将斜长石中的熔体夹杂物视为挥发性地球化学物种（如H2O，CO2）（例如H2O，CO2）等主要信息的可靠档案。 关于熔体夹杂物的起源以及它们在发生的斜长石的历史上以及它们在何时何地形成的疑问。 这项研究结合了创新的实验室实验和全面的对照校准研究，以重建来自斜长石的原始波动性组成，这些融合体的原始旋转成分是在华盛顿和加拿大边界西部的Juan de Fuca Ridge的太平洋海底上爆发的超晶状体熔岩。 实验将在斜长石和从同一样品套件中共存的橄榄石上进行实验，以相互比较并评估捕集后结晶后的程度以及重新加热的过程影响夹杂物的挥发性含量。时间序列实验将在各种温度（从1200 C到1270 C）和加热速率下进行加热阶段进行。 对夹杂物的主要元素组成的分析将通过电子微探针进行；痕量元素组成将使用激光电感耦合质谱法确定；傅立叶变换红外光谱将用于验证大包含物的二氧化碳和H2O组成。离子微探针和微射线光谱法将用于分析CO2，H2O，S和MG。 将要进行的提出的实验将确定在地壳中或通过过程中进行实验加热期间挥发物从包含物中损失的机制，例如扩散，气泡的形成以及通过晶体中的裂缝泄漏。这项研究的目标是为橄榄石和斜长石的中山山脊环境中岩浆的矿物结晶深度提供更好的测量。 要解决的问题包括包含后的夹板结晶和气泡的形成如何影响熔体夹杂物的测得的挥发性含量；不同的均质化方法和淬火率如何影响测得的挥发性含量；不同挥发性物种的测量值表明了晶体货物的形成深度和海角的二氧化碳预算；斜长石熔体夹杂物的信息与来自橄榄石熔体夹杂物的信息相比如何。这项工作的更广泛的影响包括开发新的实验技术，这些技术对其他领域具有潜在的影响，在更好地理解火山过程和理解岩浆产生的矿石沉积方面的社会影响。它还将涉及两名研究生和两名本科生的培训。