Document Type

Open Access Thesis

Embargo Period

6-27-2017

Degree Program

Geosciences

Degree Type

Master of Science (M.S.)

Year Degree Awarded

2017

Month Degree Awarded

September

Advisor Name

J. Michael Rhodes

Co-advisor Name

Stearns A. Morse

Third Advisor Name

Sheila J. Seaman

Abstract

In order to estimate the oxygen fugacity of Hawaiian lavas I have measured the ferric/ferrous ratios of samples from the 1984 eruption of Mauna Loa volcano and from the ongoing (1983-2017) Puu Oo eruption of Kilauea volcano. Fifteen samples were studied from the 21 day Mauna Loa eruption and 86 samples, erupted between 1983 and 2004, of the 34 year long Kilauea eruption. Both studies show that, in order to obtain reliable estimates of oxygen fugacity when, where, and how basaltic lava is sampled is of critical importance. Water-quenched lavas and spatter sampled at, or near vents, are less oxidized than water-quenched samples taken from open flow channels several kilometers away from the vent, or from slowly-cooled solidified flows. Additionally, samples of water-quenched lava traveling in lava tubes are less prone to oxidation than lava flowing in open channels, with oxygen fugacities similar to those of near vent quenched samples. The oxidation state of the rapidly quenched near vent or lava tube samples is at or below magnetite-wüstite (MW). This contrasts with the oxidation state of previously reported values for Hawaiian lavas, which are closer to fayalite-magnetite-quartz (FMQ) or nickel-nickel oxide (NNO). From this I conclude that the initial oxygen fugacity of Hawaiian parental magmas is close to MW and not FMQ, and that previous estimates of the oxidation state of Hawaiian magmas, based on data from solidified lava flows, were too high. This implies that the plume source of both Mauna Loa and Kilauea magmas is also close to MW, but not as reduced as the mantle source of mid-ocean ridge basalts.

Included in

Geology Commons

Share

COinS