A rapid fluctuation in the mantle source and melting history of Kilauea Volcano inferred from the geochemistry of its historical summit lavas (1790-1982)

The geochemical variations of Kilauea's historical summit lavas (1790-1982) document the short-term magmatic evolution of one of the Earth's most active volcanoes. Most of these lavas are thought to have erupted directly from the shallow (2-4 km deep) magma reservoir that underlies the volcano's summit region. This paper details a remarkable variation of lava chemistry that spans nearly the entire known compositional range of the volcano in only 200 years. The Pb, Sr, and Nd isotope and incompatible trace element ratios (e.g. La/Yb or Nb/Y) of the lavas vary systematically over time with an abrupt reversal after 1924. This rapid geochemical fluctuation records the temporal changes in the parental magma composition delivered to Kilauea's summit reservoir since 1790. The isotope and incompatible trace element ratio systematics suggest that the source region of historical Kilauea magma is both isotopically and chemically heterogeneous. These source variations can be explained by the melting of small-scale heterogeneities within the Hawaiian mantle plume. Model calculations suggest that the degree of partial melting decreased from the early 19th century until the mid-20th century, which correlates with a lower eruption rate (and presumably a lower magma supply rate) for the volcano between 1840 and 1959. This interval of declining output from the Hawaiian plume culminated with an explosive summit eruption in 1924 and the longest quiescent period in Kilauea's historical record (1934-1952). Lavas erupted just after 1924 are geochemically anomalous and may have been contaminated by the assimilation of country rock into the volcano's magma reservoir during the explosions. Subsequently, the inferred degree of partial melting and the volcano's eruption rate have increased, with the highest values since the early 19th century observed during the ongoing Puu Oo rift zone eruption.

Geologic map of Kilauea's summit region showing the distribution of historically erupted lavas. The boundary of Kilauea Caldera is shown by the heavy solid line. Pit craters, such as Halemaumau, are marked by the heavy hatchured lines, and eruptive fissures are indicated by straight or curved lines. The small dots and arrows mark the locations of samples analyzed in this study. The stippled area includes both prehistorical volcanics and tephra from historical eruptions (e.g. 1790 and 1959). The position of the Hawaiian Volcano Observatory (HVO) is provided for reference.

Temporal variations of Pb and Sr isotope and incompatible trace element ratios in Kilauea's historical summit lavas. The geochemical trends defined by the summit lavas have continued through the ongoing Puu Oo rift zone eruption (black rectangles). The vertical gray lines mark the dates of Kilauea's explosive summit eruptions in 1790 and 1924. The 1868 lava may have been stored beneath Kilauea Iki Crater for several decades prior to eruption (dashed arrow).

The short-term geochemical evolution of Kilauea Volcano. The top figures shows the volcano's eruptive history. The vertical gray lines mark the dates of Kilauea's explosive summit eruptions in 1790 and 1924. The upper panel shows the temporal variation of Kilauea's average eruption rate. The lower panel shows the eruptive activity of Kilauea's summit region (black bars) since August 1823. Eruptive activity during the late 20th century has been concentrated along the volcano's east rift zone with the sustained Mauna Ulu (1969-1974) and Puu Oo (1983 to the present) eruptions (red bars). The bottom figure shows the volcano's melting history. The results of the partial melting model suggest that the degree of partial melting has varied systematically by a factor of ~2 over the last 200 years.