V002-0007
Magma source depths and magma recycling in the 2018 eruption of Kīlauea, Hawai’i based on volatiles in melt inclusions

Monday, 7 December 2020
Poster
Allan H Lerner1, Paul J Wallace2, Thomas Shea3, Adrien Mourey3, Peter J Kelly4, Patricia Amanda Nadeau5, Tamar Elias5, Christoph Kern4, Laura E Clor4, Cheryl A Gansecki6, R. Lopaka Lee5, Lowell Moore7 and Cynthia A Werner8, (1)University of Oregon, Eugene, OR, United States, (2)University of Oregon, Department of Earth Sciences, Eugene, OR, United States, (3)University of Hawaii at Manoa, Honolulu, HI, United States, (4)USGS Cascades Volcano Observatory, Vancouver, WA, United States, (5)USGS Hawaiian Volcano Observatory, Hilo, HI, United States, (6)University of Hawaii at Hilo, Geology Department, Hilo, HI, United States, (7)Virginia Polytechnic Institute and State University, Department of Geosciences, Blacksburg, VA, United States, (8)USGS - Contractor, New Plymouth, New Zealand
Abstract:
Kīlauea Volcano’s 2018 Lower East Rift Zone (LERZ) eruption produced high lava extrusion rates, record-setting SO2 emissions, and caused a large-scale caldera collapse. Over 1 km3 of magma was cumulatively erupted (Kern et al 2020), with summit-derived basalts erupted from fissure 8 constituting 92 – 96% of the total erupted volume.

We measure mineral compositions and volatiles in melt inclusions (MI) from fissure 8 lava. Fissure 8 basalts contain low-Fo (Fo76-81) phenocryst and groundmass olivine, and high-Fo (Fo86-90) olivine with thin low-Fo rims. The low-Fo olivine are in equilibrium with the bulk LERZ melt (1140 – 1170°C) and are similar to olivine from Pu‘u ‘Ō‘ō and the Halema’uma’u lava lake. The high-Fo grains were sourced from highly primitive magmas (1260 – 1350°C) and mixed into the lower-temperature bulk LERZ melts shortly before eruption.

H2O-CO2 vapor saturation pressures in MI were determined from FTIR (glasses) and Raman (vapor bubble CO2) spectroscopy. Almost all MI in both low- and high-Fo olivine were trapped at depths ≤ 5 km (n=30). These depths are consistent with MI formation in Kīlauea’s Halema’uma’u (1 – 2 km) or South Caldera (3 – 5 km) reservoirs, and do not require deeper ascending magma to have sourced the LERZ eruption.

Melt inclusions in high-Fo olivine grains underwent > 200°C of cooling within colder LERZ melts, which caused extensive post-entrapment crystallization and sulfide precipitation in MI. However, even when accounting for sulfides in MI, many inclusions in high-Fo olivine have low S contents of 400 – 900 ppm compared to 900 – 1200 ppm in S-rich MI. A number of MI in high-Fo olivine have very low entrapment pressures (< 1 km), particularly low S concentrations (400 – 600 ppm S), and S-isotopic signatures (-1.5 to -0.5‰ δ34S) of degassed magma compared to +0.5 to +1.0‰ δ34S in S-rich glasses. This requires low pressure (< 200 m depths) S degassing from the primitive melts before MI formation.

We propose that Kīlauea’s long history of lava lake activity and lava drain-back during eruptions has recycled substantial volumes of degassed magma, including primitive magmas, into the shallow magmatic system. The last decade of degassing and magma recycling within the Halema’uma’u lava lake may have contributed to the 2018 LERZ melts being more volatile depleted than in past Kīlauea eruptions.

<< Previous Abstract | Next Abstract >>