Melt Inclusions and Their Application - New Perspective on the Subsurface Architecture of Cerro Negro Volcano, Nicaragua

Volatiles are the drivers of volcanic eruptions and monitoring and measurement in quiescent times are the key in determining when unrest within a volcanic system is beginning leading to possible cataclysms. Previous studies have focused on direct measurements from volcanic plumes or fumaroles, however, this study proposes the use of melt inclusions from tephra to determine volatile contents from the 1992 eruption of Cerro Negro Volcano, Nicaragua. The analysis of melt inclusions adds a new technique to the volatile analytical toolbox and can help to determine volatile contents from past eruptions and their subsequent evolution within a volcanic system. Though melt inclusions are easier to sample than direct degassing and ideally represent the undegassed magma at depth, they are not without complications. Vapor bubbles are almost ubiquitous within all melt inclusions and potentially contain up to 100% of the original carbon dioxide content at entrapment. If the carbon dioxide content within the vapor bubble is not considered, initial volatile content will be highly underestimated and thus depth of entrapment could be off by several kilometers. Additionally, the miscalculated carbon dioxide concentrations lead to errors in other ratios that help to determine the state of the volcanic system prior to and during eruptive events. This study will focus on determining the corrected carbon dioxide contents of melt inclusions from the 1992 erupted tephra to visualize a new subsurface architecture of Cerro Negro volcano compared to previous studies that show magma holding bodies at shallow depths. By correcting for the carbon dioxide contents within the bubble, a new schematic of the Cerro Negro plumbing system will be presented that comprises multiple interconnected magma lenses at greater depths than previously presented. This blueprint is normally suggested for spreading centers, however, this study will show that Cerro Negro is the optimal example of an arc volcano containing this subsurface architecture