Date of Award

2019

Degree Type

Thesis

Degree Name

Master of Science in Oceanography

Specialization

Marine Geology and Geophysics

Department

Oceanography

First Advisor

Katherine Kelley

Abstract

The third of five known lava balloon eruptions occurred January 1993 to March 1994 west of Socorro Island, Mexico. Large highly-vesicular basaltic scoria rose to the sea surface in pulses. Buoyant samples were collected and studied, but the submarine vent was never precisely located. New multibeam mapping and remotely operated vehicle exploration in 2017 by E/V Nautilus located and sampled the 1993 vent site, a volcaniclastic cone at 250 m depth with pillow lava and large scoria blocks. An active, low-temperature hydrothermal system (0.2°C above ambient) with white filamentous bacteria and yellow microbial mats occurs over the roughly 4000 m2 vent area. SEM imagery of fine-grained volcaniclastic sediment shows a dominance of vesicular clasts and bubble wall shards with some Limu o Pele and Pele’s hair. Some pillow tubes exhibit large interior gas cavities and expansion into vertical hornito-like structures. Observed volcanic facies at the vent site indicate that both effusive (pillow lava) and explosive (scoria, volcanic ash) activity occurred simultaneously during the 1993 submarine eruption. The generation of giant buoyant scoria was likely caused by episodic formation of a scoriaceous plug at the vent site that would fail periodically resulting in pulses of scoria being discharged. A subset of the erupted scoria was buoyant enough to reach the sea surface, the rest accumulated close to the vent. The great abundance of fine grained volcaniclastic material suggests simultaneous explosive activity likely driven mainly by primary volatile degassing. The petrogenesis and volatile degassing of magma erupted as buoyant basaltic scoria from this eruption were investigated by electron microprobe for major elements, LA-ICP-MS for trace elements, and FTIR for volatiles.

Similar to the alkaline basalts from nearby Socorro and San Benedicto Islands, recently collected seafloor samples from the 1993 Socorro submarine eruption contain 48.5-48.7 wt.% SiO2 and 5.1-5.5 wt.% Na2O+K2O. Seafloor Socorro samples are trachybasalts, matching the buoyant clasts (collected in the first 6 months of the eruption). Buoyant scoria from early in the eruption are more evolved (e.g., lower MgO) than late stage scoria collected from the seafloor. Mineral-melt evolution models indicate that fractional crystallization of a common parent magma explains shifts in major and trace elements from evolved early stage (buoyant) samples to the more primitive late stage (seafloor) clasts. Trace element patterns of the most primitive basalts have features in common with Petit spots (e.g. positive Sr and Zr anomalies [Hirano et al., 2006]), suggestive of commonalities between these different intra-plate magmatic systems. Olivine-hosted melt inclusions reveal extreme CO2-oversaturation in the melt with highs of 3929 ppm CO2 and 0.73 wt.% H2O. Volatile modeling of seafloor samples provides tentative evidence that the magma sourcing the 1993 eruption shifted from an open system degassing regime to a closed system once the magma entered a staging zone at a pressure of about 3 kbar (9-10 km). The 1993 Socorro eruptive material was sourced from a fairly homogenous parental melt with a possible shift in magma staging depths from 5 km to 9 km throughout this year-long submarine eruption.

Available for download on Sunday, August 16, 2020

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