Publication Date

Fall 2023

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Geology

Advisor

Ryan Portner; Ellen Metzger; Jonathan Miller

Abstract

This study contributes to understanding magmatic processes and the plumbing system of submarine volcanoes before, during, and after caldera formation with the use of melt inclusions (MIs). Major, trace and volatile geochemistry from both olivine and plagioclase-hosted MIs taken from volcaniclastic deposits around Axial Seamount reveal information about the storage conditions, ascent rates and eruption styles of magmas. Magma crystallizes in the subsurface, capturing MIs, and ascends where some host glasses may interact with seawater during eruption. Oversaturation in volatiles and low vesicularity show quick ascent rates. By analyzing chemical data within a pre-existing stratigraphic context this study can assess said pre- and syn-eruption processes before, during and after caldera formation. Sampling below, within and above a key marker bed of hydrothermal muddy tuff (HMT) provides a framework to interpret changing MI entrapment depths associated with an evolving magma chamber during caldera formation. Data show that (i) melt was stored in a magma chamber with a minimum depth up to 2 km below the sea floor (bsf) before caldera formation, (ii) the magma chamber emptied during caldera formation and the shallowest melt was then stored at 3.3 km bsf, and (iii) the magma chamber refilled after caldera formation where melt was once again stored at shallower depths up to 2.8 km bsf. This sequence provides a type example of MOR magma chamber evolution during caldera formation.

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