A Rapid Fluctuation in the Mantle Source and Melting History of Kilauea Volcano Inferred from the Geochemistry of its Historical Summit Lavas (1790-1982)

Abstract

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 current Puu Oo rift zone eruption.