Insights Into Mixing, Fractionation, and Degassing of Primitive Melts at Kīlauea Volcano, Hawai‘i

• Published in: Hawaiian Volcanoes Vol. 208; pp. 323 - 349
• Main Authors: Edmonds, Marie, Sides, Isobel, Maclennan, John
• Format: Book Chapter
• Language: English
• Published: United States American Geophysical Union 2015; Wiley; John Wiley & Sons, Inc
• Subjects: Hawai'i; Kīlauea volcano; magma mixing; mantle melting; melt degassing; melt inclusions; olivine fractionation; post‐entrapment crystallization; whole‐rock compositions
• ISBN: 9781118872048; 1118872045
• DOI: 10.1002/9781118872079.ch15

The nature of primitive magmas and the deep plumbing system at ocean island volcanoes is enigmatic and poorly understood. Melt inclusions provide windows into the magmatic history of primitive melts, allowing insights into melt heterogeneity, mixing, fractionation, and degassing. We present the major, trace, and volatile element composition of melt inclusions from tephra and lava samples erupted during 25 prehistoric and historic eruptions of Kīlauea Volcano over the past 600 years. Once corrected for post‐entrapment crystallization, the most primitive melts have 14.7 wt% MgO, making them close to primary. The melts form a compositional array broadly controlled by olivine fractionation, but with significant heterogeneity superimposed. This heterogeneity exceeds that observed in previous studies of whole‐rock compositions and glasses of historical Kīlauea magmas and is caused by mixing of compositionally distinct melts during fractionation. Primitive melt inclusions show a range in H 2 O contents up to ˜0.7 wt% and H 2 O/Ce up to ˜290, suggesting that some primary melts may be inherently enriched in H 2 O, inherited from the mantle melting region. Temporal trends in melt compositions are similar to those observed in whole rocks, suggesting that there are significant changes in the degree of mantle melting and mantle source composition at Kīlauea Volcano over 50–100 year timescales.