Date of Award

August 2024

Degree Type

Thesis

Degree Name

Master of Science

Department

Geosciences

First Advisor

Julie Bowles

Committee Members

Barry Cameron, Lindsay McHenry

Abstract

The Snake River Plain volcanic province stretches 600 km from eastern Oregon across southern Idaho and into northwest Wyoming. Over the past ~14 million years, olivine tholeiitic lava flows have accumulated. To assess ongoing volcanic hazards, it is important to quantify the number, timing, and size of eruptive events. This assessment requires correlating lava flows across coreholes within the Eastern Snake River Plain. Previous paleomagnetic research applied paleomagnetic inclinations to correlate flows between coreholes. This study tests whether using geomagnetic paleointensity – in addition to inclination – can increase confidence in the correlation of these flows. Pilot samples were retrieved from two core holes spaced 1.5 km apart in southeastern Idaho near the Idaho National Laboratory (INL). Susceptibility as a function of temperature was measured to determine magnetic mineralogy and any magnetic mineral alteration upon heating. The results of Thellier-type paleointensity experiments were placed into three groups based on ideal to non-ideal experimental behaviors. These behaviors can be explained by first-order reversal curves measured to assess domain state. Ideal paleointensity behavior is linked to single-domain grains typically found nearest the cooling unit margins. Non-ideal paleointensity behavior is linked to multi-domain grains found farther from these cooling unit margins. Paleointensity results allowed for the refinement of eruptive timings and inter-corehole correlations and reduced ambiguity in several cases. Tentative inclination-only data linked the Unknown 59° flow in corehole STF-AQ-01 flow to three individual eruptive episodes (Unknown 55°, Vent 5398, Unknown 56°) in corehole STF-AQ-02. A paleointensity 42.7±7.3 from Unknown 59° in STF-AQ-01, can be linked to Vent 5398 (STF-AQ-02), measured at 41.3±1.1 μT. The Unknown 55° paleointensity measurements of 27.5±0.4 μT and 28.1±2.1 μT are distinct in time from Vent 5398 in SFT-AQ-02a and from Unknown 59° in SFT-AQ-01. Furthermore, South CFA Buried Vents (STF-AQ-01 and -02) shared the same paleomagnetic inclination and at least parts of each flow shared a paleointensity of ~15 – 18 μT. However, in STF-AQ-01, the upper part of the identified flow had a distinctly higher paleointensity of 41.9±0.3 μT, indicating eruption at a different time. These results confirmed that paleomagnetic paleointensity can improve confidence in correlation when other methods led to ambiguity in eruptive timing and flow extent.

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