Mechanism of Emplacement of Flood Basalt

溢流玄武岩侵位机理

• 批准号: 9706396
• 负责人: Robert Coe
• 金额: $ 1.99万
• 依托单位: University of California-Santa Cruz
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1997
• 资助国家: 美国
• 起止时间: 1997-06-15 至 1999-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9706396&HistoricalAwards=false
• 关键词: Mechanism; Emplacement; Flood; Basalt

9706396 Coe Flood basalts are the second most significant accumulation of mafic igneous material on the surface of the Earth, and their rate of eruption has long been considered to be three to four orders of magnitude greater than occurs at present-day central basaltic volcanoes. This idea depends on the assumption that a single flow is emplaced without significant interruption. Recently it has been proposed that such flows may have grown endogenously, that is, in a multistage process by which lava is injected into the interior of an already solidified flow and jacks up the top surface. If endogenous growth is a common mechanism of emplacement, it would reduce the enormous eruption rates and associated rapid production or storage of vast quantities of melt that are required for single-stage emplacement of very large individual lava flows characteristic of these provinces. Our pilot project is to test the hypothesis of endogenous growth by determining the magnetic fabric of the Birkett flow of the Columbia River Flood Basalts, for which field observations of interior vesicle layers have already suggested the possibility of multistage emplacement. Magnetic fabric analysis can detect zones where more intense shear occurred during flow: for multistage emplacement, two or more shear boundaries should be present inside the flow. If the vesicular layers coincide with shear boundaries, consistent with the injection of lava after initial solidification, the stage will be set for a larger investigation of the role of endogenous growth in continental flood basalts.

9706396 Coe Flood玄武岩是地球表面第二大镁铁质火成岩聚集物，长期以来，它们的喷发速度一直被认为比目前中央玄武岩火山的喷发速度大三到四个数量级。这个想法依赖于这样的假设，即单个流是在没有显著中断的情况下部署的。最近有人提出，这种流动可能是内生的，也就是说，在一个多阶段的过程中，熔岩被注入已经凝固的流动的内部，并向上顶起顶部表面。如果内生增长是一种常见的侵位机制，它将减少这些省份特有的极大的单个熔岩流单级侵位所需的巨大喷发速度和相关的快速生产或储存大量熔体。我们的试点项目是通过确定哥伦比亚河洪水玄武岩的Birkett流的磁性组构来检验内生增长假说，对该玄武岩的内部泡状层的现场观察已经表明了多阶段侵位的可能性。磁性组构分析可以发现流动过程中发生强烈剪切的区域：对于多级侵位，流动内部应该存在两个或两个以上的剪切边界。如果泡状层与剪切边界重合，与初始固化后熔岩的注入一致，则将为更大范围地研究大陆溢流玄武岩中内生生长的作用奠定基础。