Mechanism of Emplacement of Flood Basalt

9706396 Coe Flood玄武岩是地球表面第二重要的镁铁质火成岩物质堆积，其喷发速率一直被认为比现在的中央玄武岩火山高出三到四个数量级。这个想法是基于一个假设，即一个单一的流动是安置没有显着的中断。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，熔岩被注入到一个已经凝固的流动的内部和顶起的顶面。如果内生增长是一种常见的侵位机制，它将减少巨大的喷发率和相关的快速生产或储存的大量熔体所需的单阶段侵位非常大的个人熔岩流的特点，这些省份。我们的试点项目是测试内生增长的假设，通过确定磁组构的伯基特流的哥伦比亚河洪水玄武岩，为内部囊泡层的实地观察已经提出了多级侵位的可能性。磁组构分析可以检测流动过程中发生更强烈剪切的区域：对于多级侵位，流动内部应该存在两个或更多剪切边界。如果泡状层与剪切边界相吻合，与初始凝固后熔岩的注入相一致，则将对大陆溢流玄武岩中内源性生长的作用进行更大规模的调查。

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.