Collaborative Research: Origins of Phenocrysts and Xenocrysts in the Bishop Tuff Rhyolitic Magma

合作研究：主教凝灰岩流纹质岩浆中斑晶和异晶的起源

• 批准号: 0001154
• 负责人: Alfred Anderson
• 金额: $ 12.35万
• 依托单位: University of Chicago
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2000
• 资助国家: 美国
• 起止时间: 2000-07-01 至 2003-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0001154&HistoricalAwards=false
• 关键词: Collaborative; Research; Origins; Phenocrysts; Xenocrysts

Anderson/WallaceEAR-0001154EAR-0001182The objectives of this study are to document the sources of crystals in the Bishop Tuff, a large volume, fragmental deposit of silicic volcanic rock that formed as a result of a huge explosive eruption, about 500 times larger than the 1980 Mt. St. Helens eruption. The crystals are important because they contain a record of processes related to how the magma formed and how and why it erupted. The traditional interpretation for the origins of such crystals is that they grow from the melt in which they erupt (such crystals are termed 'phenocrysts'). Recently, this traditional view has been challenged by those working with radiometric isotopic systems capable of providing independent measures of time. New interpretations are that most of the crystals formed a long time before eruption and were recycled from older, previously crystallized magma bodies (such crystals are termed 'xenocrysts'). Reheating of these older, largely crystalline bodies is hypothesized to have liberated crystals that became entrained in the erupting magma. In this interpretation, crystals contain little or no information about either how the magma formed or what made it erupt. Large bodies of silicic magma are an important part of planetary differentiation, and it is vital to test concepts that are related to their origin. A record of apparent formation of phenocrysts is contained in successively grown zones on crystals and in melt inclusions (now glass) that were trapped during crystal growth. We will use this record to test ideas regarding the sources of crystals in the Bishop Tuff magma. This study involves field relations of volcanic deposits, textural information, and geochemistry, and will provide an opportunity for students to learn and appreciate the need for field tests of hypothetical ideas.

安德森/华莱士-0001154岩-0001182本研究的目的是记录主教凝灰岩中晶体的来源，主教凝灰岩是一种大体积的碎屑状存款，是由于一次巨大的爆炸性喷发而形成的，比1980年Mt.圣海伦斯火山爆发。 这些晶体很重要，因为它们记录了与岩浆如何形成以及如何和为什么喷发有关的过程。 对这种晶体起源的传统解释是，它们是从它们喷发的熔体中生长出来的（这种晶体被称为“phenoconsults”）。 最近，这种传统的观点受到了那些能够提供独立时间测量的放射性同位素系统的挑战。 新的解释是，大多数晶体在喷发前很长一段时间形成，并从更古老的，以前结晶的岩浆体中回收（这种晶体被称为“捕虏体”）。 这些较老的、大部分是晶体的天体被重新加热，这被假设为释放出的晶体被夹带在喷发的岩浆中。在这种解释中，晶体包含很少或根本没有关于岩浆如何形成或喷发的信息。 大规模的岩浆是行星分化的重要组成部分，测试与其起源有关的概念至关重要。 在晶体上连续生长的区域和在晶体生长过程中被捕获的熔体包裹体（现在的玻璃）中，包含了明显形成斑晶的记录。 我们将利用这一记录来测试有关主教凝灰岩岩浆中晶体来源的想法。本研究涉及火山沉积物，结构信息和地球化学的现场关系，并将为学生提供一个学习和欣赏假设想法的现场测试的必要性的机会。